TRILL Working Group Donald Eastlake INTERNET-DRAFT Mingui Zhang Intended status: Proposed Standard Huawei Obsoletes: 7180 Radia Perlman Updates: 6325, 7177, 7179 EMC Ayan Banerjee Cisco Anoop Ghanwani Dell Sujay Gupta IP Infusion Expires: April 14, 2015 October 15, 2014 TRILL: Clarifications, Corrections, and Updates Abstract Since publication of the TRILL (Transparent Interconnection of Lots of Links) base protocol in 2011, active development of TRILL has revealed errata in RFC 6325 and areas that could use clarifications or updates. RFCs 7177, 7357, and [rfc6439bis] provide clarifications and updates with respect to Adjacency, the TRILL ESADI (End Station Address Distribution Information) protocol, and Appointed Forwarders respectively. This document provides other known clarifications, corrections, and updates. It obsoletes RFC 7180 (the previous TRILL clarifications, corrections), updates RFC 7177, updates RFC 7179, and updates RFC 6325. Status of This Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Distribution of this document is unlimited. Comments should be sent to the TRILL working group mailing list: . Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." D. Eastlake, et al [Page 1] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. D. Eastlake, et al [Page 2] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Table of Contents 1. Introduction (Changed)..................................5 1.1 Precedence (Changed)...................................5 1.2 Changes That Are Not Backward Compatible (Unchanged)...5 1.3 Terminology and Acronyms (Changed).....................6 2. Overloaded and/or Unreachable RBridges (Unchanged)......7 2.1 Reachability...........................................7 2.2 Distribution Trees.....................................8 2.3 Overloaded Receipt of TRILL Data Packets...............8 2.3.1 Known Unicast Receipt................................9 2.3.2 Multi-Destination Receipt............................9 2.4 Overloaded Origination of TRILL Data Packets...........9 2.4.1 Known Unicast Origination............................9 2.4.2 Multi-Destination Origination.......................10 2.4.2.1 An Example Network................................10 2.4.2.2 Indicating OOMF Support...........................11 2.4.2.3 Using OOMF Service................................11 3. Distribution Trees and RPF Check (Changed).............13 3.1 Number of Distribution Trees (Unchanged)..............13 3.2 Distribution Tree Update Clarification (Unchanged)....13 3.3 Multicast Pruning Based on IP Address (Unchanged).....13 3.4 Numbering of Distribution Trees (Unchanged)...........14 3.5 Link Cost Directionality (Unchanged)..................14 3.6 Alternative RPF Check (New)...........................15 3.6.1 Example of the Potential Problem....................15 3.6.2 Solution and Discussion.............................16 4. Nicknames Selection (Unchanged)........................18 5. MTU (Maximum Transmission Unit) (Unchanged)............20 5.1 MTU-Related Errata in RFC 6325........................20 5.1.1 MTU PDU Addressing..................................20 5.1.2 MTU PDU Processing..................................21 5.1.3 MTU Testing.........................................21 5.2 Ethernet MTU Values...................................21 6. TRILL Port Modes (Unchanged)...........................23 7. The CFI/DEI Bit (Unchanged)............................24 8. Other IS-IS Considerations (Changed)...................25 8.1 E-L1FS Support (New)..................................25 8.1.1 Backward Compatibility..............................25 8.1.2 E-L1FS Use for Existing (sub)TLVs...................26 8.2 Control Packet Priorities (New).......................27 8.3 Unknown PDUs (New)....................................27 8.4 Nickname Flags APPsub-TLV (New).......................28 8.5 Graceful Restart (Unchanged)..........................29 D. Eastlake, et al [Page 3] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Table of Contents (continued) 9. Updates to [RFC7177] (Adjacency) [Changed).............31 10. TRILL Header Update (New).............................32 10.1 Color Bit............................................32 10.2 Flag Word Changes (update to [RFC7179])..............33 10.2.1 Extended Hop Count.................................33 10.2.1.1 Advertising Support..............................33 10.2.1.2 Ingress Behavior.................................33 10.2.1.3 Transit Behavior.................................34 10.2.1.4 Egress Behavior..................................34 10.2.2 Extended Color Field...............................35 10.3 Updated Flag Word Summary............................35 11. IANA Considerations (Changed).........................37 11.1 Previously Completed IANA Actions (Unchanged)........37 11.2 New IANA Considerations (New)........................37 11.2.1 Reference Updated..................................37 11.2.2 The 'E' Capability Bit.............................38 11.2.3 NickFlags APPsub-TLV Number........................38 11.2.4 Update TRILL Extended Header Flags.................38 11.2.5 TRILL-VER Sub-TLV Capability Flags.................38 12. Security Considerations (Changed).....................40 Acknowledgements..........................................41 Normative References......................................42 Informative References....................................43 Appendix A: Life Cycle of a TRILL Switch Port.............45 Appendix B: Example PDUs..................................47 Appendix C: Changes from [RFC7180]........................48 C.1 Changes...............................................48 C.2 Additions.............................................48 C.2 Deletions.............................................49 Appendix Z: Change History................................50 < D. Eastlake, et al [Page 4] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 1. Introduction (Changed) Since the TRILL base protocol [RFC6325] was published in 2011, active development of TRILL has revealed errors in the specification [RFC6325] and several areas that could use clarifications or updates. [RFC7177], [RFC7357], and [rfc6439bis] provide clarifications and updates with respect to Adjacency, the TRILL ESADI (End Station Address Distribution Information) protocol, and Appointed Forwarders. This document provides other known clarifications, corrections, and updates to [RFC6325], [RFC7177], and [RFC7179]. This document obsoletes [RFC7180], the previous TRILL clarifications, corrections, and updates document. Sections of this document are annotated as to whether they are "New" technical material, material that has been technically "Changed", or material that is technically "Unchanged" by the appearance of one of these three words in parenthesis at the end of the section header. A section with only editorial changes is annotated as "(Unchanged)". If no such notation appears, then the first notation encountered on going to successively higher-level headers applies. Appendix C describes changes, summarizes material added, and lists material deleted. 1.1 Precedence (Changed) In case of conflict between this document and [RFC6325], [RFC7177], or [RFC7179] this document takes precedence. In addition, Section 1.2 (Normative Content and Precedence) of [RFC6325] is updated to provide a more complete precedence ordering of the sections of [RFC6325] as following, where sections to the left take precedence over sections to their right: 4 > 3 > 7 > 5 > 2 > 6 > 1 1.2 Changes That Are Not Backward Compatible (Unchanged) The change made by Section 3.4 below, which was also present in [RFC7180], is not backward compatible with [RFC6325] but has nevertheless been adopted to reduce distribution tree changes resulting from topology changes. The several other changes herein that are fixes to errata for [RFC6325] -- [Err3002] [Err3003] [Err3004] [Err3052] [Err3053] D. Eastlake, et al [Page 5] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates [Err3508] -- may not be backward compatible with previous implementations that conformed to errors in the specification. 1.3 Terminology and Acronyms (Changed) This document uses the acronyms defined in [RFC6325], some of which are repeated below for convenience, along with some additional acronyms and terms as follows: CFI - Canonical Format Indicator [802]. DEI - Drop Eligibility Indicator [802.1Q-2011]. EISS - Enhanced Internal Sublayer Service. OOMF - Overload Originated Multi-destination Frame. RBridge - An alternative name for a TRILL Switch. RPFC - Reverse Path Forwarding Check. SNPA - SubNetwork Point of Attachment (for example, MAC address). TRILL - Transparent Interconnection of Lots of Links (or Tunneled Routing in the Link Layer). TRILL Switch - A device implementing the TRILL protocol. An alternative name for an RBridge. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. D. Eastlake, et al [Page 6] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 2. Overloaded and/or Unreachable RBridges (Unchanged) In this Section 2, the term "neighbor" refers only to actual RBridges and ignores pseudonodes. RBridges may be in overload as indicated by the [IS-IS] overload flag in their LSPs (Link State PDUs). This means that either (1) they are incapable of holding the entire link-state database and thus do not have a view of the entire topology or (2) they have been configured to have the overload bit set. Although networks should be engineered to avoid actual link-state overload, it might occur under various circumstances. For example, if a large campus included one or more low-end TRILL Switches. It is a common operational practice to set the overload bit in an [IS-IS] router (such as a TRILL Switch) when performing maintenance on that router that might affect its ability to correctly forward packets; this will usually leave the router reachable for maintenance traffic, but transit traffic will not be routed through it. (Also, in some cases, TRILL provides for setting the overload bit in the pseudonode of a link to stop TRILL Data traffic on an access link (see Section 4.9.1 of [RFC6325]).) [IS-IS] and TRILL make a reasonable effort to do what they can even if some TRILL Switches/routers are in overload. They can do reasonably well if a few scattered nodes are in overload. However, actual least-cost paths are no longer assured if any TRILL Switches are in overload. For the effect of overload on the appointment of forwarders, see [rfc6439bis]. 2.1 Reachability Packets are not least-cost routed through an overloaded TRILL Switch, although they may originate or terminate at an overloaded TRILL Switch. In addition, packets will not be least-cost routed over links with cost 2**24 - 1 [RFC5305]; such links are reserved for traffic- engineered packets, the handling of which is beyond the scope of this document. As a result, a portion of the campus may be unreachable for least- cost routed TRILL Data because all paths to it would be through either a link with cost 2**24 - 1 or through an overloaded RBridge. For example, an RBridge (TRILL Switch) RB1 is not reachable by TRILL Data if all of its neighbors are connected to RB1 by links with cost 2**24 - 1. Such RBridges are called "data unreachable". D. Eastlake, et al [Page 7] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates The link-state database at an RBridge RB1 can also contain information on TRILL Switches that are unreachable by IS-IS link- state flooding due to link or RBridge failures. When such failures partition the campus, the TRILL Switches adjacent to the failure and on the same side of the failure as RB1 will update their LSPs to show the lack of connectivity, and RB1 will receive those updates. As a result, RB1 will be aware of the partition. Nodes on the far side of the partition are both IS-IS unreachable and data unreachable. However, LSPs held by RB1 for TRILL Switches on the far side of the failure will not be updated and may stay around until they time out, which could be tens of minutes or longer. (The default in [IS-IS] is twenty minutes.) 2.2 Distribution Trees An RBridge in overload cannot be trusted to correctly calculate distribution trees or correctly perform the RPFC (Reverse-Path Forwarding Check). Therefore, it cannot be trusted to forward multi- destination TRILL Data packets. It can only appear as a leaf node in a TRILL multi-destination distribution tree. Furthermore, if all the immediate neighbors of an RBridge are overloaded, then it is omitted from all trees in the campus and is unreachable by multi-destination packets. When an RBridge determines what nicknames to use as the roots of the distribution trees it calculates, it MUST ignore all nicknames held by TRILL Switches that are in overload or are data unreachable. When calculating RPFCs for multi-destination packets, an RBridge RB1 MAY, to avoid calculating unnecessary RPFC state, ignore any trees that cannot reach to RB1 even if other RBridges list those trees as trees that other TRILL Switches might use. (But see Section 3.) 2.3 Overloaded Receipt of TRILL Data Packets The receipt of TRILL Data packets by overloaded RBridge RB2 is discussed in the subsections below. In all cases, the normal Hop Count decrement is performed, and the TRILL Data packets is discarded if the result is less than one or if the egress nickname is illegal. D. Eastlake, et al [Page 8] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 2.3.1 Known Unicast Receipt RB2 will not usually receive unicast TRILL Data packets unless it is the egress, in which case it egresses and delivers the data normally. If RB2 receives a unicast TRILL Data packet for which it is not the egress, perhaps because a neighbor does not yet know it is in overload, RB2 MUST NOT discard the packet because the egress is an unknown nickname as it might not know about all nicknames due to its overloaded condition. If any neighbor, other than the neighbor from which it received the packet, is not overloaded, it MUST attempt to forward the packet to one of those neighbors selected at random [RFC4086]. If there is no such neighbor, the packet is discarded. 2.3.2 Multi-Destination Receipt If RB2 in overload receives a multi-destination TRILL Data packet, RB2 MUST NOT apply an RPFC since, due to overload, it might not do so correctly. RB2 egresses and delivers the frame locally where it is Appointed Forwarder for the frame's VLAN, subject to any multicast pruning. But since, as stated above, RB2 can only be the leaf of a distribution tree, it MUST NOT forward a multi-destination TRILL Data packet (except as an egressed native frame where RB2 is Appointed Forwarder). 2.4 Overloaded Origination of TRILL Data Packets Overloaded origination of unicast TRILL Data packets with known egress and of multi-destination packets is discussed in the subsections below. 2.4.1 Known Unicast Origination When an overloaded RBridge RB2 ingresses or creates a known destination unicast data packet, it delivers it locally if the destination is local. Otherwise, RB2 unicasts it to any neighbor TRILL Switch that is not overloaded. It MAY use what routing information it has to help select the neighbor. D. Eastlake, et al [Page 9] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 2.4.2 Multi-Destination Origination Overloaded RBridge RB2 ingressing or creating a multi-destination data packet is more complex than for the known unicast case as discussed below. 2.4.2.1 An Example Network For example, consider the network below in which, for simplicity, end stations and any bridges are not shown. There is one distribution tree of which RB4 is the root, as represented by double lines. Only RBridge RB2 is overloaded. +-----+ +-----+ +-----+ +-----+ | RB7 +====+ RB5 +=====+ RB3 +=====+ RB1 | +-----+ +--+--+ +-++--+ +--+--| | || | +---+---+ || | +------+RB2(ov)|======++ | | +-------+ || | | || | +--+--+ +-----+ ++==++=++ +--+--+ | RB8 +=====+ RB6 +==++ RB4 ++=====+ RB9 | +-----+ +-----+ ++=====++ +-----+ Since RB2 is overloaded, it does not know what the distribution tree or trees are for the network. Thus, there is no way it can provide normal TRILL Data service for multi-destination native frames. So RB2 tunnels the frame to a neighbor that is not overloaded if it has such a neighbor that has signaled that it is willing to offer this service. RBridges indicate this in their Hellos as described below. This service is called OOMF (Overload Originated Multi- destination Frame) service. - The multi-destination frame MUST NOT be locally distributed in native form at RB2 before tunneling to a neighbor because this would cause the frame to be delivered twice. For example, if RB2 locally distributed a multicast native frame and then tunneled it to RB5, RB2 would get a copy of the frame when RB3 transmitted it as a TRILL Data packet on the multi-access RB2-RB3-RB4 link. Since RB2 would, in general, not be able to tell that this was a frame it had tunneled for distribution, RB2 would decapsulate it and locally distribute it a second time. - On the other hand, if there is no neighbor of RB2 offering RB2 the OOMF service, RB2 cannot tunnel the frame to a neighbor. In this case, RB2 MUST locally distribute the frame where it is Appointed D. Eastlake, et al [Page 10] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Forwarder for the frame's VLAN and optionally subject to multicast pruning. 2.4.2.2 Indicating OOMF Support An RBridge RB3 indicates its willingness to offer the OOMF service to RB2 in the TRILL Neighbor TLV in RB3's TRILL Hellos by setting a bit associated with the SNPA (SubNetwork Point of Attachment, also known as MAC address) of RB2 on the link (see IANA Considerations). Overloaded RBridge RB2 can only distribute multi-destination TRILL Data packets to the campus if a neighbor of RB2 not in overload offers RB2 the OOMF service. If RB2 does not have OOMF service available to it, RB2 can still receive multi-destination packets from non-overloaded neighbors and, if RB2 should originate or ingress such a frame, it distributes it locally in native form. 2.4.2.3 Using OOMF Service If RB2 sees this OOMF (Overload Originated Multi-destination Frame) service advertised for it by any of its neighbors on any link to which RB2 connects, it selects one such neighbor by a means beyond the scope of this document. Assuming RB2 selects RB3 to handle multi-destination packets it originates, RB2 MUST advertise in its LSP that it might use any of the distribution trees that RB3 advertises so that the RPFC will work in the rest of the campus. Thus, notwithstanding its overloaded state, RB2 MUST retain this information from RB3 LSPs, which it will receive as it is directly connected to RB3. RB2 then encapsulates such frames as TRILL Data packets to RB3 as follows: M bit = 0, Hop Count = 2, ingress nickname = a nickname held by RB2, and, since RB2 cannot tell what distribution tree RB3 will use, egress nickname = a special nickname indicating an OOMF packet (see IANA Considerations). RB2 then unicasts this TRILL Data packet to RB3. (Implementation of Item 4 in Section 4 below provides reasonable assurance that, notwithstanding its overloaded state, the ingress nickname used by RB2 will be unique within at least the portion of the campus that is IS-IS reachable from RB2.) On receipt of such a packet, RB3 does the following: - changes the Egress Nickname field to designate a distribution tree that RB3 normally uses, - sets the M bit to one, D. Eastlake, et al [Page 11] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates - changes the Hop Count to the value it would normally use if it were the ingress, and - forwards the packet on that tree. RB3 MAY rate limit the number of packets for which it is providing this service by discarding some such packets from RB2. The provision of even limited bandwidth for OOMFs by RB3, perhaps via the slow path, may be important to the bootstrapping of services at RB2 or at end stations connected to RB2, such as supporting DHCP and ARP/ND (Address Resolution Protocol / Neighbor Discovery). (Everyone sometimes needs a little OOMF (pronounced "oomph") to get off the ground.) D. Eastlake, et al [Page 12] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 3. Distribution Trees and RPF Check (Changed) Two corrections, a clarification, and two updates related to distribution trees appear in the subsections below along with an alternative, stronger RPF (Reverse Path Forwarding) Check. See also Section 2.2. 3.1 Number of Distribution Trees (Unchanged) In [RFC6325], Section 4.5.2, page 56, Point 2, 4th paragraph, the parenthetical "(up to the maximum of {j,k})" is incorrect [Err3052]. It should read "(up to k if j is zero or the minimum of (j, k) if j is non-zero)". 3.2 Distribution Tree Update Clarification (Unchanged) When a link-state database change causes a change in the distribution tree(s), there are several possibilities. If a tree root remains a tree root but the tree changes, then local forwarding and RPFC entries for that tree should be updated as soon as practical. Similarly, if a new nickname becomes a tree root, forwarding and RPFC entries for the new tree should be installed as soon as practical. However, if a nickname ceases to be a tree root and there is sufficient room in local tables, the forwarding and RPFC entries for the former tree MAY be retained so that any multi-destination TRILL Data packets already in flight on that tree have a higher probability of being delivered. 3.3 Multicast Pruning Based on IP Address (Unchanged) The TRILL base protocol specification [RFC6325] provides for and recommends the pruning of multi-destination packet distribution trees based on the location of IP multicast routers and listeners; however, multicast listening is identified by derived MAC addresses as communicated in the Group MAC Address sub-TLV [RFC7176]. TRILL Switches MAY communicate multicast listeners and prune distribution trees based on the actual IPv4 or IPv6 multicast addresses involved. Additional Group Address sub-TLVs are provided in [RFC7176] to carry this information. A TRILL Switch that is only capable of pruning based on derived MAC address SHOULD calculate and D. Eastlake, et al [Page 13] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates use such derived MAC addresses from multicast listener IPv4/IPv6 address information it receives. 3.4 Numbering of Distribution Trees (Unchanged) Section 4.5.1 of [RFC6325] specifies that, when building distribution tree number j, node (RBridge) N that has multiple possible parents in the tree is attached to possible parent number j mod p. Trees are numbered starting with 1, but possible parents are numbered starting with 0. As a result, if there are two trees and two possible parents, in tree 1, parent 1 will be selected, and in tree 2, parent 0 will be selected. This is changed so that the selected parent MUST be (j-1) mod p. As a result, in the case above, tree 1 will select parent 0, and tree 2 will select parent 1. This change is not backward compatible with [RFC6325]. If all RBridges in a campus do not determine distribution trees in the same way, then for most topologies, the RPFC will drop many multi-destination packets before they have been properly delivered. 3.5 Link Cost Directionality (Unchanged) Distribution tree construction, like other least-cost aspects of TRILL, works even if link costs are asymmetric, so the cost of the hop from RB1 to RB2 is different from the cost of the hop from RB2 to RB1. However, it is essential that all RBridges calculate the same distribution trees, and thus, all must either use the cost away from the tree root or the cost towards the tree root. As corrected in [Err3508], the text in Section 4.5.1 of [RFC6325] is incorrect. It says: In other words, the set of potential parents for N, for the tree rooted at R, consists of those that give equally minimal cost paths from N to R and ... but the text should say "from R to N": In other words, the set of potential parents for N, for the tree rooted at R, consists of those that give equally minimal cost paths from R to N and ... D. Eastlake, et al [Page 14] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 3.6 Alternative RPF Check (New) [RFC6325] mandates a Reverse Path Forwarding (RPF) Check on multi- destination TRILL data packets to avoid possible multiplication and/or looping of multi-destination traffic during TRILL campus topology transients. This check is logically performed at each TRILL switch input port and determines, based on where the packet started (the ingress nickname) and the tree on which it is being distributed, whether it is arriving on the expected port. If not, the packet is silently discarded. This check is fine for point-to-point links; however, there are rare circumstances involving multi-access ("broadcast") links where a packet can be duplicated despite this RPF Check and other checks performed by TRILL. Section 3.6.1 gives an example of the potential problem and Section 3.6.2 specifies a solution. This solution is an alternative stronger RPF Check that TRILL Switches can implemented in place of the RFF Check in [RFC6325]. 3.6.1 Example of the Potential Problem Consider this network: F--A--B--C--o--D All the links except the link between C and D are point-to-point links. C and D are connected over a broadcast link represented by the pseudonode "o". For example, C and D could be connected by a bridged LAN. (Bridged LANs are transparent to TRILL.) Although the choice of root is unimportant here, assume that D or F is chosen as the root of a distribution tree so it is obvious the tree looks just like the diagram above. Now assume a link comes up from A to the same bridged LAN. The network then looks like this: +--------+ | | F--A--B--C--o--D Let's say the resulting tree in steady state includes all links except the B-C link. After the network has converged, a packet that starts out from F will go F->A. Then A will send one copy on the A-B link and another copy into the bridge LAN from which it will be received by C and D. D. Eastlake, et al [Page 15] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Now consider a transition stage where A and D have acted on the new LSPs and programmed their forwarding plane, while B and C have not yet done so. This means that B and C both consider the link between them to still be part of the tree. In this case, a packet that starts out from F and reaches A will be copied by A into the A-B link and to the bridge LAN. D's RPF check says to accept packets on this tree coming from F over its port on the bridged LAN, so it gets accepted. D is also adjacent to A on the tree, so the tree adjacency check, a separate check mandated by [RFC6325] also passes. However, the packet that gets to B gets sent out by B to C. C's RPF check still has the old state, and it thinks the packet is OK. C sends the packet along the old tree, which is into the bridge LAN. D receives one more packet, but the tree adjacency check passes at D because C is adjacent to D in the new tree as well. The RPF Check also passes at D because D's port on the bridged LAN is OK for receiving packets from F. So, during this transient state, D gets duplicates of every multi- destination packet ingressed at F (unless the packet gets pruned) until B and C act on the new LSPs and program their hardware tables. 3.6.2 Solution and Discussion The problem stems from the RPF Check in [RFC6325] depending only on the port at which a TRILL data packet is received, the ingress nickname, and the tree being used, that is, a check if {ingress nickname, tree, input port} is a valid combination according to the receiving TRILL switch's view of the campus topology. A multi-access link actually has multiple adjacencies overlaid on one physical link and to avoid the problem shown in Section 3.6.1, a stronger check is needed that includes the Layer 2 source address of the TRILL Data packet being received. (TRILL is a Layer 3 protocol and TRILL switches are true routers that logically strip the Layer 2 header from any arriving TRILL data packets and add the appropriate new Layer 2 header to any outgoing TRILL Data packet to get it to the next TRILL switch, so the Layer 2 source address in a TRILL Data packet identifies the immediately previous TRILL Switch that forwarded the packet.) What is needed, instead of checking the validity of the triplet {ingress nickname, tree, input port} is to check that the quadruplet {ingress nickname, source SNPA, tree, input port} is valid (where "source SNPA" (Sub-Network Point of Access) is the Outer.MacSA for an Ethernet link). Although it is true that [RFC6325] also requires a check that a multi-destination TRILL Data packet is from a TRILL switch that is adjacent in the distribution tree being used, this is D. Eastlake, et al [Page 16] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates a separate check from the RPF Check and these two independent checks are not as powerful as the single unified check for a valid quadruplet. However, this stronger RPF Check is not without cost. In the simple case of a multi-access link where each TRILL switch has only one port on the link, it merely increases the size of validity entries by adding the source SNPA (Outer.MacSA). However, assume some TRILL Switch RB1 has N ports attached to a multi-access link. RB1 is permitted to load split multi-destination traffic it is sending into the multi-access link across those ports (Section 4.4.4 [RFC6325]). Assume RB2 is another TRILL Switch on the link and RB2 is distribution tree adjacent to RB1. The number of validity quadruplets at RB2 for ingress nicknames whose multi-destination traffic would arrive through RB1 is multiplied by N because RB2 has to accept such traffic from any of the ports RB1 has on the access-link. Although such instances seem to be very rare in practice, N could in principle be tens or even a hundred or more ports, vastly increasing the RPF check state at RB2 when this stronger RPF check is used. Another potential cost of the stronger RPF Check is increased transient loss of multi-destination TRILL data packets during a topology change. For TRILL switch D, the new stronger RPF Check is (tree->A, Outer.MacSA=A, ingress=A, arrival port=if1) while the old one was ( tree->A, Outer.MacSA=C, ingress=A, arrival port=if1). Suppose both A and B have switched to the new tree for multicast forwarding while D has not updated its RPF Check yet, then the multicast packet will be dropped at D's if1. Since D still expects packet from "Outer.MacSA=C". But we do not have this packet loss issue if the weaker triplet check (tree->A, ingress=A, arrival port=if1) is used. Thus, the stronger check can increase the RPF Check discard of multi-destination packets during topology transients. Because of these potential costs, implementation of this stronger RPF Check is optional; however, the TRILL protocol is updated to provide that TRILL Switches MUST, for multi-destination packets, either implement the RPF and other checks in [RFC6325] or implement this stronger RPF Check as a substitute for the [RFC6325] RPF and tree adjacency checks. D. Eastlake, et al [Page 17] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 4. Nicknames Selection (Unchanged) Nickname selection is covered by Section 3.7.3 of [RFC6325]. However, the following should be noted: 1. The second sentence in the second bullet item in Section 3.7.3 of [RFC6325] on page 25 is erroneous [Err3002] and is corrected as follows: o The occurrence of "IS-IS ID (LAN ID)" is replaced with "priority". o The occurrence of "IS-IS System ID" is replaced with "seven- byte IS-IS ID (LAN ID)". The resulting corrected sentence in [RFC6325] reads as follows: "If RB1 chooses nickname x, and RB1 discovers, through receipt of an LSP for RB2 at any later time, that RB2 has also chosen x, then the RBridge or pseudonode with the numerically higher priority keeps the nickname, or if there is a tie in priority, the RBridge with the numerically higher seven-byte IS-IS ID (LAN ID) keeps the nickname, and the other RBridge MUST select a new nickname." 2. In examining the link-state database for nickname conflicts, nicknames held by IS-IS unreachable TRILL Switches MUST be ignored, but nicknames held by IS-IS reachable TRILL Switches MUST NOT be ignored even if they are data unreachable. 3. An RBridge may need to select a new nickname, either initially because it has none or because of a conflict. When doing so, the RBridge MUST consider as available all nicknames that do not appear in its link-state database or that appear to be held by IS- IS unreachable TRILL Switches; however, it SHOULD give preference to selecting new nicknames that do not appear to be held by any TRILL Switch in the campus, reachable or unreachable, so as to minimize conflicts if IS-IS unreachable TRILL Switches later become reachable. 4. An RBridge, even after it has acquired a nickname for which there appears to be no conflicting claimant, MUST continue to monitor for conflicts with the nickname or nicknames it holds. It does so by checking in LSP PDUs it receives that should update its link- state database for the following: any occurrence of any of its nicknames held with higher priority by some other TRILL Switch that is IS-IS reachable from it. If it finds such a conflict, it MUST select a new nickname, even when in overloaded state. (It is possible to receive an LSP that should update the link-state database but does not do so due to overload.) D. Eastlake, et al [Page 18] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 5. In the very unlikely case that an RBridge is unable to obtain a nickname because all valid RBridge nicknames (0x0001 through 0xFFBF inclusive) are in use with higher priority by IS-IS reachable TRILL Switches, it will be unable to act as an ingress, egress, or tree root but will still be able to function as a transit TRILL Switch. Although it cannot be a tree root, such an RBridge is included in distribution trees computed for the campus unless all its neighbors are overloaded. It would not be possible to send a unicast RBridge Channel message specifically to such a TRILL Switch [RFC7178]; however, it will receive unicast RBridge Channel messages sent by a neighbor to the Any-RBridge egress nickname and will receive appropriate multi-destination RBridge Channel messages. D. Eastlake, et al [Page 19] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 5. MTU (Maximum Transmission Unit) (Unchanged) MTU values in TRILL key off the originatingL1LSPBufferSize value communicated in the IS-IS originatingLSPBufferSize TLV [IS-IS]. The campus-wide value Sz, as described in Section 4.3.1 of [RFC6325], is the minimum value of originatingL1LSPBufferSize for the RBridges in a campus, but not less than 1470. The MTU testing mechanism and limiting LSPs to Sz assures that the LSPs can be flooded by IS-IS and thus that IS-IS can operate properly. If nothing is known about the MTU of the links or the originatingL1LSPBufferSize of other RBridges in a campus, the originatingL1LSPBufferSize for an RBridge should default to the minimum of the LSP size that its TRILL IS-IS software can handle and the minimum MTU of the ports that it might use to receive or transmit LSPs. If an RBridge does have knowledge of link MTUs or other RBridge originatingL1LSPBufferSize, then, to avoid the necessity to regenerate the local LSPs using a different maximum size, the RBridge's originatingL1LSPBufferSize SHOULD be configured to the minimum of (1) the smallest value that other RBridges are or will be announcing as their originatingL1LSPBufferSize and (2) a value small enough that the campus will not partition due to a significant number of links with limited MTU. However, as provided in [RFC6325], in no case can originatingL1LSPBufferSize be less than 1470. In a well- configured campus, to minimize any LSP regeneration due to re-sizing, all RBridges will be configured with the same originatingL1LSPBufferSize. Section 5.1 below corrects errata in [RFC6325], and Section 5.2 clarifies the meaning of various MTU limits for TRILL Ethernet links. 5.1 MTU-Related Errata in RFC 6325 Three MTU-related errata in [RFC6325] are corrected in the subsections below. 5.1.1 MTU PDU Addressing Section 4.3.2 of [RFC6325] incorrectly states that multi-destination MTU-probe and MTU-ack TRILL IS-IS PDUs are sent on Ethernet links with the All-RBridges multicast address as the Outer.MacDA [Err3004]. As TRILL IS-IS PDUs, when multicast on an Ethernet link, they MUST be sent to the All-IS-IS-RBridges multicast address. D. Eastlake, et al [Page 20] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 5.1.2 MTU PDU Processing As discussed in [RFC6325] and, in more detail, in [RFC7177], MTU- probe and MTU-ack PDUs MAY be unicast; however, Section 4.6 of [RFC6325] erroneously does not allow for this possibility [Err3003]. It is corrected by replacing Item numbered "1" in Section 4.6.2 of [RFC6325] with the following quoted text to which TRILL Switches MUST conform: "1. If the Ethertype is L2-IS-IS and the Outer.MacDA is either All- IS-IS-RBridges or the unicast MAC address of the receiving RBridge port, the frame is handled as described in Section 4.6.2.1" The reference to "Section 4.6.2.1" in the above quoted text is to that section in [RFC6325]. 5.1.3 MTU Testing The last two sentences of Section 4.3.2 of [RFC6325] have errors [Err3053]. They currently read: "If X is not greater than Sz, then RB1 sets the "failed minimum MTU test" flag for RB2 in RB1's Hello. If size X succeeds, and X > Sz, then RB1 advertises the largest tested X for each adjacency in the TRILL Hellos RB1 sends on that link, and RB1 MAY advertise X as an attribute of the link to RB2 in RB1's LSP." They should read: "If X is not greater than or equal to Sz, then RB1 sets the "failed minimum MTU test" flag for RB2 in RB1's Hello. If size X succeeds, and X >= Sz, then RB1 advertises the largest tested X for each adjacency in the TRILL Hellos RB1 sends on that link, and RB1 MAY advertise X as an attribute of the link to RB2 in RB1's LSP." 5.2 Ethernet MTU Values originatingL1LSPBufferSize is the maximum permitted size of LSPs starting with the 0x83 Intradomain Routeing Protocol Discriminator byte. In Layer 3 IS-IS, originatingL1LSPBufferSize defaults to 1492 bytes. (This is because, in its previous life as DECnet Phase V, IS- IS was encoded using the SNAP SAP (Sub-Network Access Protocol D. Eastlake, et al [Page 21] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Service Access Point) [RFC7042] format, which takes 8 bytes of overhead and 1492 + 8 = 1500, the classic Ethernet maximum. When standardized by ISO/IEC [IS-IS] to use Logical Link Control (LLC) encoding, this default could have been increased by a few bytes but was not.) In TRILL, originatingL1LSPBufferSize defaults to 1470 bytes. This allows 27 bytes of headroom or safety margin to accommodate legacy devices with the classic Ethernet maximum MTU despite headers such as an Outer.VLAN. Assuming the campus-wide minimum link MTU is Sz, RBridges on Ethernet links MUST limit most TRILL IS-IS PDUs so that PDUz (the length of the PDU starting just after the L2-IS-IS Ethertype and ending just before the Ethernet Frame Check Sequence (FCS)) does not to exceed Sz. The PDU exceptions are TRILL Hello PDUs, which MUST NOT exceed 1470 bytes, and MTU-probe and MTU-ack PDUs that are padded by an amount that depends on the size being tested (which may exceed Sz). Sz does not limit TRILL Data packets. They are only limited by the MTU of the devices and links that they actually pass through; however, links that can accommodate IS-IS PDUs up to Sz would accommodate, with a generous safety margin, TRILL Data packet payloads of (Sz - 24) bytes, starting after the Inner.VLAN and ending just before the FCS. Most modern Ethernet equipment has ample headroom for frames with extensive headers and is sometimes engineered to accommodate 9K byte jumbo frames. D. Eastlake, et al [Page 22] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 6. TRILL Port Modes (Unchanged) Section 4.9.1 of [RFC6325] specifies four mode bits for RBridge ports but may not be completely clear on the effects of various combinations of bits. The table below explicitly indicates the effect of all possible combinations of the TRILL port mode bits. "*" in one of the first four columns indicates that the bit can be either zero or one. The following columns indicate allowed frame types. The Disable bit normally disables all frames, but, as an implementation choice, some or all low-level Layer 2 control message can still be sent or received. Examples of Layer 2 control messages are those control frames for Ethernet identified in Section 1.4 of [RFC6325] or PPP link negotiation messages [RFC6361]. +-+-+-+-+--------+-------+-------+-------+-------+ |D| | | | | | | | | |i| |A| | | | TRILL | | | |s| |c|T| |native | Data | | | |a| |c|r| |ingress| | | | |b|P|e|u| | | LSP | | | |l|2|s|n|Layer 2 |native | SNP | TRILL | P2P | |e|P|s|k|Control |egress | MTU | Hello | Hello | +-+-+-+-+--------+-------+-------+-------+-------+ |0|0|0|0| Yes | Yes | Yes | Yes | No | +-+-+-+-+--------+-------+-------+-------+-------+ |0|0|0|1| Yes | No | Yes | Yes | No | +-+-+-+-+--------+-------+-------+-------+-------+ |0|0|1|0| Yes | Yes | No | Yes | No | +-+-+-+-+--------+-------+-------+-------+-------+ |0|0|1|1| Yes | No | No | Yes | No | +-+-+-+-+--------+-------+-------+-------+-------+ |0|1|0|*| Yes | No | Yes | No | Yes | +-+-+-+-+--------+-------+-------+-------+-------+ |0|1|1|*| Yes | No | No | No | Yes | +-+-+-+-+--------+-------+-------+-------+-------+ |1|*|*|*|Optional| No | No | No | No | +-+-+-+-+--------+-------+-------+-------+-------+ The formal name of the "access bit" above is the "TRILL traffic disable bit". The formal name of the "trunk bit" is the "end-station service disable bit" [RFC6325]. D. Eastlake, et al [Page 23] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 7. The CFI/DEI Bit (Unchanged) In May 2011, the IEEE promulgated [802.1Q-2011], which changed the meaning of the bit between the priority and VLAN ID bits in the payload of C-VLAN tags. Previously, this bit was called the CFI (Canonical Format Indicator) bit [802] and had a special meaning in connection with IEEE 802.5 (Token Ring) frames. Now, under [802.1Q-2011], it is a DEI (Drop Eligibility Indicator) bit, similar to that bit in S-VLAN/B-VLAN tags where this bit has always been a DEI bit. The TRILL base protocol specification [RFC6325] assumed, in effect, that the link by which end stations are connected to TRILL Switches and the restricted virtual link provided by the TRILL Data packet are IEEE 802.3 Ethernet links on which the CFI bit is always zero. Should an end station be attached by some other type of link, such as a Token Ring link, [RFC6325] implicitly assumed that such frames would be canonicalized to 802.3 frames before being ingressed, and similarly, on egress, such frames would be converted from 802.3 to the appropriate frame type for the link. Thus, [RFC6325] required that the CFI bit in the Inner.VLAN, which is shown as the "C" bit in Section 4.1.1 of [RFC6325], always be zero. However, for TRILL Switches with ports conforming to the change incorporated in the IEEE 802.1Q-2011 standard, the bit in the Inner.VLAN, now a DEI bit, MUST be set to the DEI value provided by the EISS (Enhanced Internal Sublayer Service) interface on ingressing a native frame. Similarly, this bit MUST be provided to the EISS when transiting or egressing a TRILL Data packet. As with the 3-bit Priority field, the DEI bit to use in forwarding a transit packet MUST be taken from the Inner.VLAN. The exact effect on the Outer.VLAN DEI and priority bits and whether or not an Outer.VLAN appears at all on the wire for output frames may depend on output port configuration. TRILL campuses with a mixture of ports, some compliant with [802.1Q-2011] and some compliant with pre-802.1Q-2011 standards, especially if they have actual Token Ring links, may operate incorrectly and may corrupt data, just as a bridged LAN with such mixed ports and links would. D. Eastlake, et al [Page 24] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 8. Other IS-IS Considerations (Changed) This section covers E-L1FS Support, Control Packet Priorities, Unknown PDUs, the Nickname Flags APPsub-TLV, and Graceful Restart. 8.1 E-L1FS Support (New) TRILL switches MUST support Extended Level 1 Flooding Scope PDUs (E- L1FS) [RFC7356] and MUST include a Scoped Flooding Support TLV [RFC7356] in all TRILL Hellos they send indicating support for this scope and any other FS-LSP scopes that they support. This support increases the number of fragments available for link state information by over two orders of magnitude. (See Section 9 for further information on support of the Scoped Flooding Support TLV.) In addition, TRILL switches MUST advertise their support of E-L1FS flooding in a TRILL Version sub-TLV capability bit (see [RFC7176] and Section 11.2). This bit is used by a TRILL switch, say RB1, to determine support for E-L1FS by some remote RBx. The alternative of simply looking for an E-L1FS FS-LSP originated by RBx fails because (1) RBx might support E-L1FS flooding but not be originating any E- L1FS FS-LSPs and (2) even if RBx is originating E-L1FS FS-LSPs there might, due to legacy TRILL switches in the campus, be no path between RBx and RB1 through TRILL switches supporting E-L1FS flooding. If that were the case, no E-L1FS FS-LSP originated by RBx could get to RB1. 8.1.1 Backward Compatibility A TRILL campus might contain TRILL switches supporting E-L1FS flooding and legacy TRILL switches that do not support E-L1FS or perhaps do not support any [RFC7356] scopes. A TRILL switch conformant to this document can always tell which adjacent TRILL switches support E-L1FS flooding from the adjacency table entries on its ports (see Section 9). In addition, such a TRILL switch can tell which remote TRILL switches in a campus support E- L1FS by the presence of a TRILL Version sub-TLV in that TRILL switch's LSP with the E-L1FS support bit set in the Capabilities field; this capability bit is ignored for adjacent TRILL switches for which only the adjacency table entry is consulted to determine E-L1FS support. TRILL specifications making use of E-L1FS MUST specify how situations D. Eastlake, et al [Page 25] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates involving mixed TRILL campus of TRILL switches will be handled. 8.1.2 E-L1FS Use for Existing (sub)TLVs In a campus where all TRILL switches support E-L1FS, all TRILL sub- TLVs listed in Section 2.3 of [RFC7176], except the TRILL Version sub-TLV, MAY be advertised by inclusion in Router Capability or MT- Capability TLVs in E-L1FS FS-LSPs [RFC7356]. (The TRILL Version sub- TLV still MUST appear in an LSP fragment zero.) In a mixed campus where some TRILL switches support E-L1FS and some do not, then only the following four sub-TLVs of those listed in Section 2.3 of [RFC7176] can appear in E-L1FS and then only under the conditions discussed below. In the following list, each sub-TLV is preceded by an abbreviated acronym used only in this Section 8.1.2: IV: Interested VLANs and Spanning Tree Roots sub-TLV VG: VLAN Groups sub-TLV IL: Interested Labels and Spanning Tree Roots sub-TLV LG: Label Groups sub-TLV An IV or VG sub-TLV MUST NOT be advertised by TRILL switch RB1 in an E-L1FS FS-LSP and MUST be advertised in an LSP unless the following conditions are met: - E-L1FS is supported by all of the TRILL switches that are data reachable from RB1 and are interested in the VLANs mentioned in the IV or VG sub-TLV, and - there is E-L1FS connectivity between all such TRILL switches in the campus interested in the VLANs mentioned in the IV or VG sub- TLV (connectivity involving only intermediate TRILL switches that also support E-L1FS). Any IV and VG sub-TLVs MAY still be advertised via core TRILL IS-IS LSP by any TRILL switch that has enough room in its LSPs. The conditions for using E-L1FS for the IL and LG sub-TLVs are the same as for IV and VG but with Fine Grained Labels [RFC7172] substituted for VLANs. Note, for example, that the above would permit a contiguous subset of the campus that supported Fine Grained Labels and E-L1FS to use E-L1FS to advertise IL and LG sub-TLVs even if the remainder of the campus did not support Fine Grained Labels or E-L1FS. D. Eastlake, et al [Page 26] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 8.2 Control Packet Priorities (New) When deciding what packet to send out a port, control packets used to establish and maintain adjacency between TRILL switches SHOULD be treated as being in the highest priority category. This includes TRILL IS-IS Hello and MTU PDUs and possibly other adjacency [RFC7177] or link technology specific packets. Other control and data packets SHOULD be given lower priority so that a flood of such other packets cannot lead to loss of or inability to establish adjacency. Loss of adjacency causes a topology transient that can result in reduced throughput, reordering, increased probability of loss of multi- destination data, and, if the adjacency is a cut point, network partitioning. Other important control packets should be given second highest priority. Lower priorities should be given to data or less important control packets. Control packets can be ordered into priority classes as shown below. Although few implementations will actually treat all of these classes differently, higher numbered classes SHOULD NOT be treated as higher priority than lower numbered class. There may be additional control packets, not specifically listed in any category below, that SHOULD be handled as being in the most nearly analogous category. 1. Hello, MTU-probe, MTU-ack, and other packets critical to establishing and maintaining adjacency. 2. LSPs, CSNP/PSNPs, and other important control packets, 3. Circuit scoped FS-LSP, FS-CSNP, and FS-PSNPs. 4. Non-circuit scoped FS-LSP, FS-CSNP, and FS-PSNPs. 8.3 Unknown PDUs (New) TRILL switches MUST silently discard [IS-IS] PDUs they receive with PDU numbers they do not understand, just as they ignore TLVs and sub- TLVs they receive that have unknown Types and sub-Types; however, they SHOULD maintain a counter of how many such PDUs have been received, on a per PDU number basis. (This is not burdensome as the PDU number is only a 5-bit field.) Note: The set of valid [IS-IS] PDUs was stable for so long that some IS-IS implementations may treat PDUs with unknown PDU numbers as a serious error and, for example, an indication that other valid PDUs from the sender are not to be trusted or that D. Eastlake, et al [Page 27] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates they should drop adjacency to the sender if it was adjacent. However, the MTU-probe and MTU-ack PDUs were added by [RFC7176] and now [RFC7356] has added three more new PDUs. While the authors of this document are not aware of any Internet drafts calling for further PDUs, the eventual addition of further new PDUs should not be surprising. 8.4 Nickname Flags APPsub-TLV (New) An optional Nickname Flags APPsub-TLV within the TRILL GENINFO TLV [RFC7357] is specified below. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | Type = NickFlags (#tbd2) | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | Length = 4*K | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NICKFLAG RECORD 1 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ ... +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NICKFLAG RECORD K | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ Where each NICKFLAG RECORD has the following format: +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | Nickname | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |IN| RESV | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ o Type: NickFlags TRILL APPsub-TLV, set to tbd2 (NICKFLAGS) o Length: 4 times the number of NICKFLAG RECORDS present. o Nickname: A 16-bit TRILL nickname held by the advertising TRILL switch ([RFC6325] and Section 4). o IN: Ingress. If this flag is one, it indicates the advertising TRILL switch may use the nickname in the NICKFLAG RECORD as the ingress nickname of TRILL Headers it creates. If the flag is zero, that nickname will not be used for that purpose. o RESV: Reserved for additional flags to be specified in the future. MUST be sent as zero and ignored on receipt. D. Eastlake, et al [Page 28] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates A NICKFLAG RECORD is ignored if the nickname it lists is not a nickname owned by the TRILL switch advertising the enclosing NickFlags APPsub-TLV. If a TRILL switch intends to use a nickname in the ingress nickname field of TRILL Headers it constructs, it can advertise this through E-L1FS FS-LSPs (see Section 8.1) using a NickFlags APPsub-TLV entry with the IN flag set. If it owns only one nickname, there is no reason to do this because, if a TRILL switch advertises no NickFlags APPsub-TLVs with the IN flag set for nicknames it owns, it is assumed that the TRILL switch might use any or all nicknames it owns as the ingress nickname in TRILL Headers it constructs. Every reasonable effort should be made to be sure that Nickname sub- TLVs [RFC7176] and NickFlags APPsub-TLVs remain in sync. If all TRILL switches in a campus support E-L1FS, so that Nickname sub-TLVs can be advertised in E-L1FS FS-LSPs, then the Nickname sub-TLV and any NickFlags APP-subTLVs for any particular nickname should be advertised in the same fragment. If they are not in the same fragment then, to the extent practical, all fragments involving those sub-TLVs for the same nickname should be propagated as an atomic action. If a TRILL switch sees multiple NickFlags APPsub-TLV entries for the same nickname, it assumes that nickname might be used as the ingress in a TRILL Header if any of the NickFlags APPsub-TLV entries have the IN bit set. It is possible that a NickFlags APPsub-TLV would not be propagated throughout the TRILL campus due to legacy TRILL switches not supporting E-L1FS. In that case, Nickname sub-TLVs must be advertised in LSPs and TRILL switches not receiving NickFlags APPsub-TLVs having entries with the IN flag set will simply assume that the source TRILL switch might use any of its nicknames as ingress in constructing TRILL Headers. Thus the use of this optional APPsub-TLV is backwards compatible with legacy lack of E-L!FS support. Additional flags may be assigned for other purposes out of the RESV field for other purposes in the future. 8.5 Graceful Restart (Unchanged) TRILL Switches SHOULD support the features specified in [RFC5306], which describes a mechanism for a restarting IS-IS router to signal to its neighbors that it is restarting, allowing them to reestablish their adjacencies without cycling through the down state, while still correctly initiating link-state database synchronization. If this feature is not supported, it may increase the number of topology transients cause by a TRILL switch rebooting due to errors or D. Eastlake, et al [Page 29] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates maintenance. D. Eastlake, et al [Page 30] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 9. Updates to [RFC7177] (Adjacency) [Changed) To support the E-L1FS flooding scope [RFC7356] mandated by Section 8.1 and backwards compatibility with legacy RBridges not supporting E-L1FS flooding, the following updates are made to [RFC7177]: 1. The list in the second paragraph of [RFC7177] Section 3.1 has the following item added: - The Scoped Flooding Support TLV. In addition, the sentence immediately after that list is modified to read as follows: Of course, the priority, Desired Designated VLAN, Scoped Flooding Support TLV, and possibly the inclusion or value of the PORT- TRILL-VER sub-TLV, and/or BFD-Enabled TLV can change on occasion, but then the new value(s) must similarly be used in all TRILL Hellos on the LAN port, regardless of VLAN. 2. An additional bullet item is added to the end of Section 3.2 of [RFC7177] as follows: o The value from the Scoped Flooding Support TLV or a null string if none was included. 3. Near the bottom of Section 3.3 of [RFC7177] a bullet item as follows is added: o The variable length value part of the Scoped Flooding Support TLV in the Hello or a null string if that TLV does not occur in the Hello. 4. At the beginning of Section 4 of [RFC7177], a bullet item is added to the list as follows: o The variable length value part of the Scoped Flooding Support TLV used in TRILL Hellos sent on the port. D. Eastlake, et al [Page 31] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 10. TRILL Header Update (New) The TRILL header has been updated from its original specification in [RFC6325] by [TRILL-OAM-FM] and [RFC7179] and is further updated by this document. The TRILL header is now as show below and is followed by references for all of the fields. Those fields for which the reference is only to [RFC6325] are unchanged from that RFC. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | V |A|C|M|Ex-Length| Hop Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Egress Nickname | Ingress Nickname | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : Optional Flag Word : +-+-+-+-+-+-+-+-+-+-+-+- In calculating a TRILL data packet hash as part of equal-cost multi- path selection, a TRILL switch MUST ignore the value of the "A" and "C" bits. o V (Version): 2-bit unsigned integer. See Section 3.2 of [RFC6325]. o A (Alert): 1 bit. See [TRILL-OAM-FM]. o C (Color): 1 bit. See Section 10.1. o M (Multi-destination): 1 bit. See Section 3.4 of [RFC6325]. o Ex-Length: 5 bits. Header extensions length, see Section 3.5 of [RFC6325] and Section 10.2 below. If this field is non-zero, then the optional Flag Word listed below is present. o Hop Count: 6 bits. See Section 3.6 of [RFC6325]. o Egress Nickname. See Section 3.7.1 of [RFC6325]. o Ingress Nickname. See Section 3.7.2 of [RFC6325]. o Optional Flag Word: See [RFC7179] and Section 10.2. 10.1 Color Bit The Color bit provides an optional way by which ingress TRILL switches MAY mark TRILL Data packets for implementation specific purposes. Transit TRILL switches MUST NOT change this bit. Transit and egress TRILL switches MAY use the Color bit for implementation dependent traffic labeling or statistical or other traffic study or D. Eastlake, et al [Page 32] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates analysis. 10.2 Flag Word Changes (update to [RFC7179]) When the extension length field is non-zero, the first 32 bits after the Ingress nickname field provides additional flags. These bits are as specified in [RFC7179] except as changed by the subsections below that provide extended Hop Count and extended Color fields. See Section 10.3 for a diagram and summary of these fields. 10.2.1 Extended Hop Count The TRILL base protocol [RFC6325] specifies the Hop Count field in the header, to avoid packets persisting in the network due to looping or the like. However, the Hop Count field size (6 bits) limits the maximum hops a TRILL data packet can traverse to 64. Optionally, TRILL switches can use a field composed of bits 14 through 16 in the Flag Word, as specified below. to extend this field to 9 bits. This increases the maximum Hop Count to 512. Use of Hop Counts in excess of 64 requires support of this optional capability at all TRILL switches along the path of a TRILL Data packet. 10.2.1.1 Advertising Support In case of a TRILL campus such that the unicast calculated path, plus a reasonable allowance for alternate pathing, or the distribution tree calculated path, traverse more than 64 hops, it may be that not all the TRILL switches support the extended Hop Count mechanism. As such it is required that TRILL switches advertise their support by setting bit 14 in the TRILL Version Sub-TLV Capabilities and Header Flags Supported field [RFC7176]; bits 15 and 16 of that field are now specified as Unassigned (see Section 11.2.5). 10.2.1.2 Ingress Behavior If an ingress TRILL switch determines it should set the hop count for a TRILL Data packet to 63 or less, then behavior is as specified in the TRILL base protocol [RFC6325]. If hop count for a TRILL Data D. Eastlake, et al [Page 33] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates packet should be set to some value greater than 63 but less than 512 and all TRILL switches that the packet is reasonably likely to encounter support extended Hop Count, then the resulting TRILL Header has the Flag Word extension present, the high order three bits of the desired hop count are stored in the extended Hop Count field in the Flag Word, the five low order bits are stored in the Hop Count filed in the first word of the TRILL Header, and bit two (the Critical Reserved bit of the Critical Summary Bits) in the Flag Word is set. For known unicast traffic (TRILL Header M bit zero), when an ingress TRILL switch determines that the least cost path to the egress is more than 64 hops but not all TRILL switches on that path support the extended Hop Count feature, the frame is discarded. For multi-destination traffic, when a TRILL switch determines that one or more tree path from the ingress it more than 64 hops but not all TRILL switches in the campus support the extended Hop Count feature, the encapsulation uses a total Hop Count of 63 to obtain at least partial distribution of the traffic. 10.2.1.3 Transit Behavior A transit TRILL switch supporting extended Hop Count behaves like a base protocol [RFC6325] TRILL switch in decrementing the hop count except that it considers the hop count to be a 9 bit file where the extended Hop Count field consistutes the high order three bits. To be more precise: a TRILL switch supporting extended Hop Count takes the first of the following actions that is applicable: 1. If both the Hop Count and extended Hop Count fields are zero, the packet is discarded. 2. If the Hop Count is non-zero, it is decremented. As long as the extended Hop Count is non-zero, no special action is taken if the result of this decrement is zero and the packet is processed normally. 3. If the Hop Count is zero, it is set to the maximum value of 63 and the extended Hop Count is decremented. 10.2.1.4 Egress Behavior No special behavior is required when egressing a TRILL Data packet D. Eastlake, et al [Page 34] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates that uses the extended Hop Count. The Flag Word, if present, is removed along with the rest of the TRILL Header during decapsulation. 10.2.2 Extended Color Field Flag Word bits 27 and 28 are specified to be a two-bit Extended Color field (see Section 10.3). These bits are in the non-critical ingress- to-egress region of the Flag Word. The Extended Color field provides an optional way by which ingress TRILL switches MAY mark TRILL Data packets for implementation specific purposes. Transit TRILL switches MUST NOT change this bit. Transit and egress TRILL switches MAY use the Color bit for implementation dependent traffic labeling or statistical or other traffic study or analysis. As provided in Section 2.3.1 of [RFC7176], support for these bits is indicated by the same bits (27 and 28) in the Capabilities and Header Flags Supported field of the TRILL Version Sub-TLV. In the spirit of indicating support, a TRILL switch that sets or senses the Extended Color field SHOULD set the corresponding 2-bit field in the TRILL Version Sub-TLV non-zero. The meaning of the possible non-zero values (1, 2 or 3) is implementation dependent. 10.3 Updated Flag Word Summary With the changes above, the 32-bit Flag Word extension to the TRILL Header [RFC7179], appearing as the "TRILL Extended Header Flags" registry on the TRILL Parameters IANA web page, is now as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Crit.| CHbH | NCHbH |CRSV | NCRSV | CItE | NCItE | |.....|.........|...........|.....|.......|...........|.........| |C|C|C| |C|N| | Ext | | |Ext| | |R|R|R| |R|C| | Hop | | |Clr| | |H|I|R| |C|C| | Cnt | | | | | |b|t|s| |A|A| | | | | | | |H|E|v| |F|F| | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Bit 0 to 2 are the Critical Summary bits as specified in [RFC7179] consisting of the Critical Hop-by-Hop, Critial Ingres-to-Egress, and D. Eastlake, et al [Page 35] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Critial Reserved bits, respectively. The next two fields are specific Critial and Non-Critical Hop-by-Hop bits, CHbH and NCHbH, respectively, containing the Critial and Non-Critical Channel Alert flags as specified in [RFC7179]. The next field is the Critical Reserved bits (CRSV) that are specified herein to be the Extended Hop Count. Then the Non-Critical Reserved Bits (NCRSV) and the Critial Ingress-to-Egress bits (CITE) as specified in [RFC7179]. Finally, there is the Non-Critical Ingress-to-Egress field, the top two bits of which are specified herein as the Extended Color field. D. Eastlake, et al [Page 36] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 11. IANA Considerations (Changed) This section give IANA actions previously completed and newly requested IANA actions. 11.1 Previously Completed IANA Actions (Unchanged) The following IANA actions were completed as part of [RFC7180] and are included here for completeness, since this document obsoletes [RFC7180]. 1. The nickname 0xFFC1, which was reserved by [RFC6325], is allocated for use in the TRILL Header Egress Nickname field to indicate an OOMF (Overload Originated Multi-destination Frame). 2. Bit 1 from the seven previously reserved (RESV) bits in the per- neighbor "Neighbor RECORD" in the TRILL Neighbor TLV [RFC7176] is allocated to indicate that the RBridge sending the TRILL Hello volunteers to provide the OOMF forwarding service described in Section 2.4.2 to such frames originated by the TRILL Switch whose SNPA (MAC address) appears in that Neighbor RECORD. The description of this bit is "Offering OOMF service". 3. Bit 0 is allocated from the Capability bits in the PORT-TRILL-VER sub-TLV [RFC7176] to indicate support of the VLANs Appointed sub- TLV [RFC7176] and the VLAN inhibition setting mechanisms specified in [rfc6439bis]. The description of this bit is "Hello reduction support". 11.2 New IANA Considerations (New) The following are new IANA actions for this document: 11.2.1 Reference Updated All references to [RFC7180] in the TRILL Parameters Registry are replaced with references to this document except that the Reference for bit 0 in the PORT-TRILL-VER Sub-TLV Capapbilty Flags is changed to [rfc6439bis]. D. Eastlake, et al [Page 37] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 11.2.2 The 'E' Capability Bit IANA is requested to allocate a previously reserved capability bit in the TRILL Version sub-TLV carried in the Router Capability and MT Capability TLVs (#242, #144) to indicate support of the [RFC7356] E- L1FS flooding scope. This capability bit is referred to as the "E" bit. The following is the addition to the Bit Description References ---- --------------------- --------------- tbd1 E-L1FS FS-LSP support [this document][RFC7356] 11.2.3 NickFlags APPsub-TLV Number IANA is requested to allocate an APPsub-TLV number under the TRILL GENINFO TLV from the range less than 255. Type Name References ---- --------- ----------- tbd2 NICKFLAGS [this document] 11.2.4 Update TRILL Extended Header Flags Update the "TRILL Extended Header Flags" registry as follows: Bits Purpose References ----- ---------------------------------------------- ---------- 14-16 Extended Hop Count [this document] 27-28 Extended Color [this document] 29-31 Available non-critical ingress-to-egress flags [RFC7179] [this document] 11.2.5 TRILL-VER Sub-TLV Capability Flags Update the "TRILL-VER Sub-TLV Capapbility Flags" registry as follows: D. Eastlake, et al [Page 38] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Bit Description Reference ----- -------------------------- ---------------- 14 Extended Hop Count support [this document] 15-16 Unassigned [this document] 27-28 Extended Color support [this document] 29-31 Extended header flag support [RFC7179] [this document] D. Eastlake, et al [Page 39] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 12. Security Considerations (Changed) This memo improves the documentation of the TRILL protocol, corrects five errata in [RFC6325], updates [RFC6325], [RFC7177], and [RFC7179] and obsoletes [RFC7180]. It does not change the Security Considerations of these RFCs to which the reader is referred. {{ Probably need to say more than this. }} D. Eastlake, et al [Page 40] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Acknowledgements The contributions of the following individuals to this document are gratefully acknowledged: Santosh Rajagopalan The contributions of the following, listed in alphabetic order, to the preceding version of this document, [RFC7180], are gratefully acknowledged: Somnath Chatterjee, Weiguo Hao, Rakesh Kumar, Yizhou Li, Radia Perlman, Mike Shand, Meral Shirazipour, and Varun Shah. D. Eastlake, et al [Page 41] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Normative References [802.1Q-2011] - IEEE, "IEEE Standard for Local and metropolitan area networks -- Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks", IEEE Std 802.1Q-2011, August 2011. [IS-IS] - International Organization for Standardization, "Intermediate System to Intermediate System intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode network service (ISO 8473)", Second Edition, November 2002. [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5305] - Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, October 2008. [RFC5306] - Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS", RFC 5306, October 2008. [RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A. Ghanwani, "Routing Bridges (RBridges): Base Protocol Specification", RFC 6325, July 2011. [RFC6361] - Carlson, J. and D. Eastlake 3rd, "PPP Transparent Interconnection of Lots of Links (TRILL) Protocol Control Protocol", RFC 6361, August 2011. [RFC7172] - Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and D. Dutt, "Transparent Interconnection of Lots of Links (TRILL): Fine-Grained Labeling", RFC 7172, May 2014. [RFC7176] - Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt, D., and A. Banerjee, "Transparent Interconnection of Lots of Links (TRILL) Use of IS-IS", RFC 7176, May 2014. [RFC7177] - Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and V. Manral, "Transparent Interconnection of Lots of Links (TRILL): Adjacency", RFC 7177, May 2014. [RFC7179] - Eastlake 3rd, D., Ghanwani, A., Manral, V., Li, Y., and C. Bestler, "Transparent Interconnection of Lots of Links (TRILL): Header Extension", RFC 7179, May 2014, . [RFC7356] - Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding Scope Link State PDUs (LSPs)", RFC 7356, September 2014, . D. Eastlake, et al [Page 42] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Informative References [802] - IEEE 802, "IEEE Standard for Local and metropolitan area networks: Overview and Architecture", IEEE Std 802.1-2001, 8 March 2002. [Err3002] - RFC Errata, Errata ID 3002, RFC 6325, . [Err3003] - RFC Errata, Errata ID 3003, RFC 6325, . [Err3004] - RFC Errata, Errata ID 3004, RFC 6325, . [Err3052] - RFC Errata, Errata ID 3052, RFC 6325, . [Err3053] - RFC Errata, Errata ID 3053, RFC 6325, . [Err3508] - RFC Errata, Errata ID 3508, RFC 6325, . [RFC4086] - Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005, . [RFC6327] - Eastlake 3rd, D., Perlman, R., Ghanwani, A., Dutt, D., and V. Manral, "Routing Bridges (RBridges): Adjacency", RFC 6327, July 2011, . [RFC6439] - Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F. Hu, "Routing Bridges (RBridges): Appointed Forwarders", RFC 6439, November 2011, . [RFC7042] - Eastlake 3rd, D. and J. Abley, "IANA Considerations and IETF Protocol and Documentation Usage for IEEE 802 Parameters", BCP 141, RFC 7042, October 2013. [RFC7175] - Manral, V., Eastlake 3rd, D., Ward, D., and A. Banerjee, "Transparent Interconnection of Lots of Links (TRILL): Bidirectional Forwarding Detection (BFD) Support", RFC 7175, May 2014. [RFC7178] - Eastlake 3rd, D., Manral, V., Li, Y., Aldrin, S., and D. Ward, "Transparent Interconnection of Lots of Links (TRILL): RBridge Channel Support", RFC 7178, May 2014. [RFC7180] - Eastlake 3rd, D., Zhang, M., Ghanwani, A., Manral, V., D. Eastlake, et al [Page 43] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates and A. Banerjee, "Transparent Interconnection of Lots of Links (TRILL): Clarifications, Corrections, and Updates", RFC 7180, May 2014. [RFC7357] - Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O. Stokes, "Transparent Interconnection of Lots of Links (TRILL): End Station Address Distribution Information (ESADI) Protocol", RFC 7357, September 2014, . [TRILL-OAM-FM] - Senevirathen, T., "TRILL Fault Management", draft- ietf-trill-oam-fm, work in progress. [rfc6439bis] - Eastlake, D., et al., "TRILL: Appointed Forwarders", draft-eastlake-trill-rfc6439bis, work in progress. D. Eastlake, et al [Page 44] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Appendix A: Life Cycle of a TRILL Switch Port The contents of this informational Appendix are based on http://www.ietf.org/mail-archive/web/trill/current/msg06355.html Question: Suppose we are developing a TRILL implementation to run on different machines. Then what happened 1st? Is LSP or ESADI started first? -> Link state database creation -> Designated RBridge election (How to set priority? any fixed process that depends on user settings? ) -> etc. ? Answer: The first thing that happens on a port/link is any link set-up that is needed. For example, on a PPP link [RFC6361], you need to negotiate that you will be using TRILL. However, if you have Ethernet links [RFC6325], which are probably the most common type, there isn't any link set-up needed. Then TRILL IS-IS Hellos get sent out the port to be exchanged on the link [RFC7177]. Optionally, you might also exchange MTU- probe/ack PDUs [RFC7177], BFD PDUs [RFC7175], or other link test packets. But all these other things are optional. Only Hellos are required. TRILL doesn't send anything else on the link until the link gets out of the Down or Detect states [RFC7177]. If a link is configured as a point-to-point link, there is no Designated RBridge (DRB) election. By default, an Ethernet link is considered a LAN link and the DRB election occurs when the link is in any state other than Down. You don't have to configure priorities for each TRILL switch (RBridge) to be Designated RBridge (DRB). Things will work fine with all the RBridges on a link using default priority. But if the network manager wants to control this, they should be a way for them to configure the priorities to be DRB. (To avoid complexity, this appendix generally describes things for a link that only has two TRILL switches on it. But TRILL works fine as currently specified on a broadcast link with multiple TRILL switches on it - actually multiple TRILL switch ports since a TRILL switch can have multiple ports connected to the same link. The most likely way to get such a multi-access link with current technology is to have more than 2 TRILL switch Ethernet ports connected to a bridged LAN. Since the TRILL protocol operates above all bridging, to the first approximation, the bridge LAN looks like a transparent broadcast link to TRILL.) When a link gets to the 2-Way or Report state, then LSP, CSNP, and PSNP start to flow on the link (as well as FS-LSPs, FS-CSNPs, and D. Eastlake, et al [Page 45] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates FS-PSNPs if the TRILL switch is using E-L1FS (see Section 8.1)). When a link gets to the Report state, then there is adjacency. The existence of that adjacency is flooded (reported) to the campus in LSPs. TRILL data packets can then start to flow on the link as TRILL switches recalculate the least cost paths and distribution trees to take the new adjacency into account. (Until it gets to the Report state, there is no adjacency and no TRILL data packets can flow over that link (with the minor corner case exception that an RBridge Channel message can, for its first hop only, be sent on a port where there is no adjacency (Section 2.4 of [RFC7178]).) (Although this paragraph seems to be talking about link state, it is actually port state. It is possible for different TRILL switch ports on the same link to temporarily be in different states. The adjacency state machinery runs independently on each port.) ESADI [RFC7357] is built on top of the regular TRILL routing. Since ESADI PDUs look, to transit TRILL switches, like regular TRILL data packets, no ESADI PDUs can flow until adjacencies are established and TRILL data is flowing. Of course, ESADI is optional and is not used unless configured... Question: Does it require TRILL Full headers at the time TRILL-LSPs start being broadcast on a link? Because at that time it's not defined Egress and Ingress nicknames. Answer: TRILL Headers are only for TRILL Data packets. TRILL IS-IS packets, such as TRILL-LSPs, are sent in a different way that does not use a TRILL Header and does not depend on nicknames. Probably, in most implementations, a TRILL switch will start up using the same nickname it had when it shut down or last got disconnected from a campus. If you want, you can implement TRILL to come up initially not reporting any nickname (by not including an Nickname sub-TLV in its LSPs) until you get the link state database or most of the link state database, and then choose a nickname no other TRILL switch in the campus is using. Of course, if a TRILL switch does not have a nickname, then it cannot ingress data, cannot egress known unicast data, and cannot be a tree root. TRILL IS-IS and LSPs and the link state database all work based on the 7-byte IS-IS System-ID (sometimes called the LAN ID). System- IDs always have to be unique across the campus so there is no problem determining topology regardless of nickname state. The Nickname system is built on top of that. D. Eastlake, et al [Page 46] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Appendix B: Example PDUs [Three for four example PDUs to be included here to help answer any questions about bit ordering or the like.] D. Eastlake, et al [Page 47] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Appendix C: Changes from [RFC7180] This informational Appendix summarizes the changes, augmentations, and excisions this document makes to [RFC7180]. C.1 Changes For each heading in this document ending with "(Changed)", this section summarizes how it was changed: Section 1, Introduction: numerous changes to reflect the overall changes in contents. Section 1.1, Precedence: changed to add mention of [RFC7179]. Section 1.3, Terminology and Acronyms: numerous terms added. Section 3, Distribution Trees and RPF Check: changed by the addition of the new material in Section 3.6. See C.2 item 1. Section 8, Other IS-IS Considerations: Changed by the addition of Sections 8.1, 8.2, 8.3, and 8.4. See Appendix C.2 items 2, 3, 4, and 5 respectively. Section 9, Updates to [RFC7177] (Adjacency): Changes and additions to [RFC7177] to support E-L1FS. See Appendix C.2, item 2. Section 11, IANA Considerations: changed by the addition of material in Section 11.2. See Appendix C.2, item 7. Section 12, Security Considerations: minor changes in the RFCs listed. C.2 Additions The following material was added to [RFC7180] in producing this document: D. Eastlake, et al [Page 48] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates 1. Addition of support for an alternative Reverse Path Forwarding Check (RPFC) along with considerations for deciding between the original [RFC6325] RPFC and this alternative RPFC. This alternative RPFC was originally discussed on the TRILL WG mailing list in http://www.ietf.org/mail- archive/web/trill/current/msg01852.html and subsequent messages. (Section 3.6) 2. Addition of mandatory E-L1FS [RFC7356] support (Section 8.1, Section 9). 3. Recommendations concerning control packet priorities. (Section 8.2) 4. Implementation requirements concerning unknown IS-IS PDU types (Section 8.3). 5. Specification of an optional Nickname Flags APPsub-TLV and an ingress flag within that APPsub-TLV. (Section 8.4) 6. Update TRILL Header to allocate a Color bit (Section 10.1) and update the optional TRILL Header Extension Flag Word to allocate a two-bit Extended Color field (Section 10.2). 7. Add IANA Considerations in Section 11.2. C.2 Deletions The following material was deleted from [RFC7180] in producing this document: 1. Removal of all updates to [RFC6327] that occurred in [RFC7180]. These have been rolled into [RFC7177] that obsoletes [RFC6327]. However, new updates to [RFC7177] are included (see Item 1 in Section A.1). 2. Removal of all updates to [RFC6439]. These have been rolled into [rfc6439bis] that will obsolete [RFC6439]. D. Eastlake, et al [Page 49] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Appendix Z: Change History This appendix will list changes in subsequent versions of this document. D. Eastlake, et al [Page 50] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Authors' Addresses Donald Eastlake 3rd Huawei Technology 155 Beaver Street Milford, MA 01757 USA Phone: +1-508-333-2270 EMail: d3e3e3@gmail.com Mingui Zhang Huawei Technologies Co., Ltd Huawei Building, No.156 Beiqing Rd. Z-park, Shi-Chuang-Ke-Ji-Shi-Fan-Yuan, Hai-Dian District, Beijing 100095 P.R. China EMail: zhangmingui@huawei.com Radia Perlman EMC 2010 256th Avenue NE, #200 Bellevue, WA 98007 USA Email: radia@alum.mit.edu Ayan Banerjee Cisco EMail: ayabaner@cisco.com Anoop Ghanwani Dell 5450 Great America Parkway Santa Clara, CA 95054 USA EMail: anoop@alumni.duke.edu Sujay Gupta IP Infusion, RMZ Centennial Mahadevapura Post Bangalore - 560048 India EMail: sujay.gupta@ipinfusion.com D. Eastlake, et al [Page 51] INTERNET-DRAFT TRILL: Clarifications, Corrections, and Updates Copyright and IPR Provisions Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. D. Eastlake, et al [Page 52]