Network Working Group Eric Gray, Editor Internet Draft Ericsson Expires: September, 2007 March 5, 2007 The Architecture of an RBridge Solution to TRILL draft-ietf-trill-rbridge-arch-02.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on September 5, 2007. Abstract RBridges are link layer (L2) devices that use routing protocols as a control plane. They combine several of the benefits of the link layer with network layer routing benefits. RBridges use existing link state routing (without requiring configuration) to improve RBridge to RBridge aggregate throughput. RBridges also Gray Expires September, 2007 [Page 1] Internet-Draft RBridge Architecture March 2007 provide support for IP multicast and IP address resolution optimizations. They are intended to be applicable to similar L2 network sizes as conventional bridges and are intended to be backward compatible with those bridges as both ingress/egress and transit. They also support VLANs (although this generally requires configuration) and otherwise attempt to retain as much 'plug and play' as is already available in existing bridges. This document proposes an RBridge system as a solution to the TRILL problem. It also defines the RBridge architecture, defines its terminology, and describes basic components and desired behavior. One or more separate documents specify the protocols and mechanisms that satisfy the architecture presented herein. Gray Expires September, 2007 [Page 2] Internet-Draft RBridge Architecture March 2007 Table of Contents 1. Introduction................................................4 2. Background..................................................6 2.1. Existing Terminology...................................6 2.2. RBridge Terminology...................................10 3. Components.................................................13 3.1. RBridge Device........................................13 3.2. RBridge Data Model....................................14 3.2.1. CFT..............................................14 3.2.2. CFT-RDT..........................................14 3.2.3. CTT..............................................16 4. Functional Description.....................................16 4.1. CRED Auto-configuration...............................17 4.2. RBridge Peer Discovery................................19 4.3. Tunneling.............................................20 4.4. RBridge General Operation.............................21 4.5. Ingress/Egress Operations.............................22 4.6. Transit Forwarding Operations.........................24 4.6.1. Unicast..........................................24 4.6.2. Broadcast, Multicast and Flooding................24 4.6.2.1. Broadcast...................................25 4.6.2.2. Multicast...................................26 4.6.2.3. Flooding....................................27 4.7. Routing Protocol Operation............................28 4.8. Other Bridging and Ethernet Protocol Operations.......29 4.8.1. Wiring Closet Problem............................29 5. How RBridges Address the TRILL Problem Space...............31 6. Conclusions................................................31 7. Security Considerations....................................32 8. IANA Considerations........................................32 9. Acknowledgments............................................32 10. References................................................33 10.1. Normative References.................................33 10.2. Informative References...............................33 Author's Addresses............................................34 Intellectual Property Statement...............................34 Disclaimer of Validity........................................35 Copyright Statement...........................................35 Acknowledgment................................................35 Gray Expires September, 2007 [Page 3] Internet-Draft RBridge Architecture March 2007 1. Introduction This document describes an architecture that addresses the TRILL problem and applicability statement [2]. This architecture describes a solution that is composed of a set of devices called RBridges. RBridges cooperate together within an Ethernet network to provide a layer two delivery service that makes efficient use of available links using a link state routing protocol. The service provided is analogous to creation of a single, virtual device composed of an overlay of tunnels, constructed between RBridge devices, using link state routing. RBridges thus support increased RBridge to RBridge bandwidth and fault tolerance, when compared to conventional Ethernet bridges (which forward frames via a spanning tree), while still being compatible with bridges and hubs. The principal objectives of this architecture is to provide an overview of the use of these RBridges in meeting the following goals: 1) Provide a form of optimized layer two delivery service. 2) Use existing technology as much as possible. 3) Allow for configuration free deployment. In providing a (optimized) layer two (L2) service, key factors we want to maintain are: transparency to higher layer (layer 3 and above) delivery services and mechanisms, and use of location independent addressing. Optimization of the L2 delivery service consists of: use of an optimized subset of all available paths and support for optimization of ARP/ND and pruning of multicast traffic delivery paths. To accomplish the goal of using existing technologies as much as possible, we intend to specify minimal extensions (if required) to one or more existing link-state routing protocols, as well as defining the specific sub-set of existing bridging technologies this architecture is intended to makes use of. The extent to which routing protocol extensions may be required depends on the closeness of the "fit" of any chosen routing protocol to RBridge protocol requirements. See [6] for further information on these requirements. The use of a specific routing protocol - along with appropriate extensions and enhancements - will be defined in corresponding RBridge protocol specifications (see [3] for example). Gray Expires September, 2007 [Page 4] Internet-Draft RBridge Architecture March 2007 Specific protocol specifications will also describe the details of interactions between the RBridge protocol and specific L2 technologies - i.e. - Virtual Local Area Networking (VLAN), L2 Multicast, etc. This document describes the general nature of the RBridge solution without restricting related specifications. As an overview, however, the intention is to use a link-state routing protocol to accomplish the following: 1) Discover RBridge peers. 2) Determine RBridge link topology. 3) Advertise L2 reachability information. 4) Establish L2 delivery using shortest path (verses STP). There are additional RBridge protocol requirements - above and beyond those addressed by any existing routing protocol - that are identified in this document and need to be addressed in corresponding RBridge protocol specifications. To allow for configuration free deployment, specific protocol specifications should explicitly define the conditions under which RBridges may - and may not - be deployed as-is (plug and play), and the mechanisms that are required to allow this. For example, the first requirement any RBridge protocol must meet is to derive information required by link-state routing protocol(s) for protocol start-up and communications between peers - such as higher-layer addressing and/or identifiers, encapsulation header information, etc. At the abstract level, RBridges need to maintain the following information: 1) Peer information, 2) Topology information, 3) Forwarding information - a. unicast, b. flooded, and c. multicast. Gray Expires September, 2007 [Page 5] Internet-Draft RBridge Architecture March 2007 In addition, RBridge specifications may suggest (or require) the maintenance of other information as needed to support ARP/ND and multicast optimizations. Peer information may be acquired via the routing protocol, or may be discovered as a result of RBridge-specific peer discovery mechanisms. Topology information is expected to be acquired via the link-state routing protocol. Forwarding information is derived from the combination of attached MAC address learning, snooping of multicast-related protocols (e.g. - IGMP), and routing advertisements and path computations using the link-state routing protocol. Other information - such as the mapping of MAC and IP addresses, or multicast pruning information - may be learned using snooping of ARP/ND or IGMP (for example) and it is possible that RBridges may need to participate actively in these protocols. The remainder of this document outlines the TRILL architecture of an RBridge-based solution and describes RBridge components, interactions and functions. Note that this document is not intended to represent the only solution to the TRILL problem statement, nor does it specify the protocols that instantiate this architecture - or that only one such set of protocols is prescribed. The former may be contained in other architecture documents and the latter would be contained in separate specification documents (see - e.g. - [3]). 2. Background This architecture is based on the RBridge system described in an Infocom paper [1]. That paper describes the RBridge system as a specific instance; this document abstracts architectural features only. The remainder of this section describes the terminology of this document, which may differ from that of the original paper. 2.1. Existing Terminology The following terminology is defined in other documents. A brief definition is included in this section for convenience and - in some cases - to remove any ambiguity in how the term may be used in this document, as well as in derivative documents intended to specify components, protocol, behavior and encapsulation relative to the architecture described in this document. Gray Expires September, 2007 [Page 6] Internet-Draft RBridge Architecture March 2007 o 802: IEEE Specification for the Ethernet architecture, i.e., including hubs and bridges. o 802.1D: IEEE Specification for bridged Ethernet, including the BPDUs used in spanning tree protocol (STP) [5]. o ARP: Address Resolution Protocol - a protocol used to find an address of form X, given a corresponding address of form Y. In this document, ARP refers to the well-known protocol used to find L2 (MAC) addresses, using a given L3 (IP) address. See [10] for further information on IP ARP. o Bridge: an Ethernet (L2, 802.1D) device with multiple ports that receives incoming frames on a port and transmits them on zero or more of the other ports; bridges support both bridge learning and STP. Transparent bridges do not modify the L2 PDU being forwarded. o Bridge Learning: process by which a bridge determines on which single outgoing port to transmit (forward or copy) an incoming unicast frame. This process depends on consistent forwarding as "learning" uses the source MAC address of frames received on each interface. Layer 2 (L2) forwarding devices "learn" the location of L2 destinations by peeking at layer 2 source addresses during frame forwarding, and store the association of source address and receiving interface. L2 forwarding devices use this information to create "filtering database" entries and - gradually - eliminate the need for flooding. o Bridge Protocol Data Unit (BPDU): the frame type associated with bridge control functions (for example: STP/RSTP). o Bridge Spanning Tree (BST): an Ethernet (L2, 802.1D) forwarding protocol based on the topology of a spanning tree. o Broadcast Domain: the set of (layer 2) devices that must be reached (or reachable) by (layer 2) broadcast traffic injected into the domain. o Broadcast Traffic: traffic intended for receipt by all devices in a broadcast domain. o Ethernet: See "802" above. Gray Expires September, 2007 [Page 7] Internet-Draft RBridge Architecture March 2007 o Filtering Database - database containing association information of (source layer 2 address, arrival interface). The interface that is associated with a specific layer 2 source address, is the same interface which is used to forward frames having that address as a destination. When a layer 2 forwarding device has no entry for the destination layer 2 address of any frame it receives, the frame is "flooded". o Flooded Traffic - traffic forwarded on all interfaces, except those on which it was received, within the same broadcast domain. Flooding is the mechanism by which traffic is delivered to a destination that is currently "unknown" (i.e. - either not yet "learned", or aged out of the "filtering database"). o Flooding - the process of forwarding traffic to ensure that frames reach all possible destinations when the destination location is not known. In "flooding", an 802.1D forwarding device forwards a frame for any destination not "known" (i.e. - not in the filtering database) on every active interface except that one on which it was received. See also VLAN flooding. o Frame: in this document, frame refers to an Ethernet (L2) unit of transmission (PDU), including header, data, and trailer (or payload and envelope). o Hub: an Ethernet (L2, 802) device with multiple ports which transparently transmits frames arriving on any port to all other ports. This is a functional definition, as there are devices that combine this function with certain bridge-like functions that may - under certain conditions - be referred to as "hubs". o IGP: Interior Gateway Protocol - any of the potential (link- state) routing protocols candidates considered as potentially useful RBridge routing protocols. o IS-IS: Intermediate System to Intermediate System routing protocol. See [8] for further information on IS-IS. o LAN: Local Area Network. A LAN is an L2 forwarding domain. This term is synonymous with Ethernet Subnet in the context of this document. Gray Expires September, 2007 [Page 8] Internet-Draft RBridge Architecture March 2007 o MAC: Media Access Control - mechanisms and addressing for L2 frame forwarding. o Multicast Forwarding: forwarding methods that apply to frames with broadcast or multicast destination MAC addresses. o Node: a device with an L2 (MAC) address that sources and/or sinks L2 frames. o OSPF: Open Shortest Path First routing protocol. See [7] and [9] for further information on OSPF. o Packet: in this document, packet refers to L3 (or above) data transmission units (PDU - e.g. - an IP Packet (RFC791 [4]), including header and data. o PDU: Protocol Data Unit - unit of data to be transmitted by a protocol. To distinguish L2 and L3 PDUs, we refer to L2 PDUs as "frames" and L3 PDUs as "packets" in this (and related) document(s). o Router: a device that performs IP (L3) forwarding (the "routing function"); RBridges typically do not span routers (i.e. - provide a connection from one router interface to another router interface on the same router). o Routing Function: in this document, the "routing function" consists of forwarding IP packets between L2 broadcast domains, based on L3 addressing and forwarding information. In the process of performing the "routing function", devices (typically routers) usually forward packets from one L2 broadcast domain to another (one, or more in the IP multicast case) - distinct - L2 broadcast domain(s). RBridges cannot span the routing function. o Segment: an Ethernet link, either a single physical link or emulation thereof (e.g., via hubs) or a logical link or emulation thereof (e.g., via bridges). o Spanning Tree Protocol (STP): an Ethernet (802.1D) protocol for establishing and maintaining a single spanning tree among all the bridges on a local Ethernet segment. Also, Rapid Spanning Tree Protocol (RSTP). In this document, STP and RSTP are considered to be the same. o Spanning Tree Table (STT): a table containing port activation status information as determined during STP. Gray Expires September, 2007 [Page 9] Internet-Draft RBridge Architecture March 2007 o SPF: Shortest Path First - an algorithm name associated with routing, used to determine a shortest path graph traversal. o Subnet, Ethernet: a single segment, or a set of segments interconnected by a CRED (see section 2.2); in the latter case, the subnet may or may not be equivalent to a single segment. Also a subnet may be referred to as a broadcast domain or LAN. By definition, all nodes within an Ethernet Subnet (broadcast domain or LAN) must have L2 connectivity with all other nodes in the same Ethernet subnet. o TRILL: Transparent Interconnect over Lots of Links - the working group and working name for the problem domain to be addressed in this document. o Unicast Forwarding: forwarding methods that apply to frames with unicast destination MAC addresses. o Unknown Destination - a destination for which a receiving device has no filtering database entry. Destination (layer 2) addresses are typically "learned" by (layer 2) forwarding devices via a process commonly referred to as "bridge learning". o VLAN: Virtual Local Area Network. VLANs in general fall into two categories: link (or port) specific VLANs and tagged VLANs. In the former case, all frames forwarded and all directly connected nodes are assumed to be part of a single VLAN. In the latter case, VLAN tagged frames are used to distinguish which VLAN each frame is intended for. o VLAN Flooding: flooding as described previously, except that frames are only forwarded on those interfaces configured for participation in the applicable VLAN. 2.2. RBridge Terminology The following terms are defined in this document and intended for use in derivative documents intended to specify components, protocol, behavior and encapsulation relative to the architecture specified in this document. o CRED: Cooperating RBridges and Encapsulation Tunnels - a topological construct consisting of a set of cooperating RBridges, and the forwarding tunnels connecting them. Gray Expires September, 2007 [Page 10] Internet-Draft RBridge Architecture March 2007 o CRED Forwarding Table (CFT): the per-hop forwarding table populated by the RBridge Routing Protocol; forwarding within the CRED is based on a lookup of the CRED Transit Header (CTH) encapsulated within the outermost received L2 header. The outermost L2 encapsulation in this case includes the source MAC address of the immediate upstream RBridge transmitting the frame and destination MAC address of the receiving RBridge for use in the unicast forwarding case. o CFT-RDT: a forwarding table used for propagation of broadcast, multicast or flooded frames along the RBridge Distribution Tree (RDT). o CRED Transit Header (CTH): a 'shim' header that encapsulates the ingress L2 frame and persists throughout the transit of a CRED, which is further encapsulated within a hop-by-hop L2 header (and trailer). The hop-by-hop L2 encapsulation in this case includes the source MAC address of the immediate upstream RBridge transmitting the frame and destination MAC address of the receiving RBridge - at least in the unicast forwarding case. o CRED Transit Table (CTT): a table that maps ingress frame L2 destinations to egress RBridge addresses, used to determine encapsulation of ingress frames for transit of the CRED. o Cooperating RBridges - those RBridges within a single Ethernet Subnet (broadcast domain or LAN) not having been configured to ignore each other. By default, all RBridges within a single Ethernet subnet will cooperate with each other. It is possible for implementations to allow for configuration that will restrict "cooperation" between an RBridge and an apparent neighboring RBridge. One reason why this might occur is if the trust model that applies in a particular deployment imposes a need for configuration of security information. By default no such configuration is required however - should it be used in any specific scenario - it is possible (either deliberately or inadvertently) to configure neighboring RBridges so that they do not cooperate. In the remainder of this document, all RBridges are assumed to be in a cooperating (default) configuration. Gray Expires September, 2007 [Page 11] Internet-Draft RBridge Architecture March 2007 o Designated RBridge (DR): the RBridge associated with ingress and egress traffic to a particular Ethernet link having shared access among multiple RBridges; that RBridge is such a link's "Designated RBridge". The Designated RBridge is determined by an election process among those RBridges having shared access via a single Segment. o Edge RBridge (edge of a CRED): describes RBridges that serve to ingress frames into the CRED and egress frames from the CRED. L2 frames transiting an RBridge CRED enter, and leave, it via an edge RBridge. o Egress RBridge: for any specific frame, the RBridge through which that frame leaves the CRED. For frames transiting a CRED, the egress RBridge is an edge RBridge where RBridge encapsulation is removed from the transit frames prior to exiting the CRED. o Forwarding Tunnels: in this document, CRED Forwarding Tunnels (or Forwarding Tunnels) is used to refer to the paths for forwarding transit frames, encapsulated at an RBridge ingress and decapsulated at an RBridge egress. o Ingress RBridge: for any specific frame, the RBridge through which that frame enters the CRED. For frames transiting a CRED, the ingress RBridge is the edge RBridge where RBridge encapsulation is added to the transit traffic entering the CRED. o LPT: Learned Port Table. See Filtering Database. o RBridge: a logical device as described in this document, which incorporate both routing and bridging features, thus allowing for the achievement of TRILL Architecture goals. A single RBridge device which can cooperate with other RBridge devices to create a CRED. o RBridge Distribution Tree: a tree computed for each edge RBridge - and potentially for each VLAN in which that RBridge participates - for delivery of broadcast, multicast and flooded frames from that RBridge to all relevant egress RBridges. This is the point-to-multipoint delivery tree used by an ingress RBridge to deliver multicast, broadcast or flooded traffic. The tree consists of a set of one or more next-hops to be used when the ingress RBridge receives a multicast or broadcast frame (frame with a multicast or broadcast destination address), or frame with unknown Gray Expires September, 2007 [Page 12] Internet-Draft RBridge Architecture March 2007 destination addresses. If forwarding frames hop-by-hop, next hop RBridges will, in turn, have a similar set of one or more next-hops to be used for forwarding these frames - when received from an upstream, or ingress, RBridge. This progression continues until frames arrive at egress RBridges. 3. Components A CRED is composed of RBridge devices and the forwarding tunnels that connect them; all other Ethernet link subnet devices, such as bridges, hubs, and nodes, operate conventionally in the presence of an RBridge. 3.1. RBridge Device An RBridge is a device - having some of the characteristics of both bridges and routers - that forwards frames on an Ethernet link segment. It has one or more Ethernet ports which may be wired or wireless; the particular physical layer is not relevant. An RBridge is defined more by its behavior than its structure, although it contains three tables which distinguish it from conventional bridges. Conventional bridges contain a learned port table (LPT), or filtering database, and a spanning tree table (STT). The LPT allows a bridge to avoid flooding all received frames, as is typical for a hub or repeater. The bridge learns which nodes are accessible from a particular port by assuming bi-directional consistency: the source addresses of incoming frames indicate that the incoming port is to be used as output for frames destined to that address. Incoming frames are checked against the LPT and forwarded to the particular port if a match occurs, otherwise they are flooded out all active ports (except the incoming port). The STT indicates the ports used in the spanning tree. Details of STP operation are out of scope for this document, however the result of STP is to disable ports which would otherwise result in more than one path traversal of the spanning tree. RBridges, by comparison, have a CRED Forwarding Table (CFT - used for unicast forwarding of RBridge encapsulated frames across the CRED), CFT-RDT (used for flooding, broadcast or multicast forwarding of RBridge encapsulated frames across the CRED) and a CRED Transit Table (CTT - used by the ingress RBridge to determine what encapsulation to use for frames Gray Expires September, 2007 [Page 13] Internet-Draft RBridge Architecture March 2007 received as un-encapsulated from non-RBridge devices), described in the following sections. 3.2. RBridge Data Model The following tables represent the logical model of the data required by RBridges in forwarding unicast and multicast data across a CRED. 3.2.1. CRED Forwarding Table (CFT) The CFT is a forwarding table for unicast traffic within the CRED, allowing tunneled traffic to transit the CRED from ingress to egress. The size of a fully populated CFT at each RBridge is maximally bounded by the product of the number of directly connected RBridge peers (where "directly connected" in this context refers to RBridges connected to each other without transiting one or more additional RBridges) and VLANs. RBridges may have separate CFTs for each VLAN, if this is supported by configuration. The CFT is continually maintained by RBridge routing protocol (see Section 4.7). The CFT contains data specific to RBridge forwarding for unicast traffic. The specific fields contained in this table are to be defined in RBridge protocol specifications. In the abstract, however, the table should contain forwarding direction and encapsulation associated with an RBridge encapsulated frame received - determined by the "shim" header destination and VLAN (if applicable). 3.2.2. CRED Forwarding Table (CFT-RDT) The CFT-RDT consists of a set of forwarding entries used for support of RBridge Distribution Trees (RDT). CFT-RDT entries are distinct from typical CFT entries because there may be zero or more of them that match for any incoming frame. The CFT-RDT may be part of the CFT, or instantiated as a separate table, in implementations. In discussing entries to be included in the CFT-RDT, the following entities are temporarily defined, or further qualified: o Root RBridge - the RBridge that is the head end of an RDT. All RBridges within a CRED are potential ingress RBridges. Gray Expires September, 2007 [Page 14] Internet-Draft RBridge Architecture March 2007 o Egress RBridge - an RBridge that is the tail end of a path corresponding to a specific CFT-RDT entry. All RBridges within a CRED are potential egress RBridges. Not all RBridges within a CRED will be on the shortest path between any ingress RBridge and any other egress RBridge. o Local RBridge - the RBridge that forms and maintains the CFT- RDT entry (or entries) under discussion. The local RBridge may be a root RBridge, or an egress RBridge with respect to any set of entries in the CFT-RDT. o RBridge CRED Egress Interface - an interface on any RBridge where a transit RBridge encapsulated frame would be decapsulated prior to forwarding. With respect to such an interface, the local RBridge is the egress RBridge. Each local RBridge will maintain a set of entries for at least the following - corresponding to a subset of all possible forwarding paths: o Zero or more entries grouped for each root RBridge - keyed by the root RBridge identifier - used to determine forwarding of broadcast, multicast, and flooded frames originally RBridge encapsulated by that ingress within the CRED. o Corresponding to each of these entry groups, one entry for each of zero or more egress RBridge - where the local RBridge is on the shortest path toward that egress RBridge. o Corresponding to each of these entry groups, one entry for each of zero or more CRED egress interfaces. Each entry would contain an indication of which single interface a broadcast, multicast or flooded frame would be forwarded for each (root RBridge, egress RBridge) pair. Entries would also contain any required encapsulation information, etc. required for forwarding on a given interface, and toward a corresponding specific egress RBridge. A local RBridge could maintain a full set of entries from every RBridge to every other RBridge, however - depending on topology - only a subset of these entries would ever be used. In addition, a topology change that changed selection of shortest paths would also very likely change other elements of the entries, negating possible benefits from having pre-computed CFT-RDT entries. Gray Expires September, 2007 [Page 15] Internet-Draft RBridge Architecture March 2007 CFT-RDT entries should also include VLAN identification information relative to each set of ingress RBridge, to allow scoping of broadcast, multicast and flooding forwarding by configured VLANs. CFT-RDT entries should also include Multicast-Group Address specific information relative to each egress RBridge that is a member of a given well-known multicast group, to allow scoping of multicast forwarding by multicast group. Implicit in this data model is the assumption that the "shim" header encapsulation will contain information that explicitly identifies the CRED ingress RBridge for any broadcast, multicast or flooded frame. How the CFT-RDT is maintained will be defined in appropriate protocol specifications used to instantiate this architecture. The protocol specification needs to include mechanisms and procedures required to establish and maintain the CFT-RDT in consideration of potential SPF recomputations resulting from network topology changes. 3.2.3. CRED Transit Table (CTT) The CTT determines how arriving traffic will be encapsulated, for forwarding to the egress RBridge, via the CRED. The CTT can be considered a version of the LPT that treats the CRED, as a whole, as another port. It becomes configured in much the same way as the LPT: by snooping incoming traffic, and assuming bi- directional consistency. The information is learned at the egress RBridge and propagated to all other RBridges in the CRED via the RBridge routing protocol. The CTT may be as large as the number of nodes on the Ethernet subnet, across all VLANs. RBridges may have separate CTTs for each VLAN, if separate VLANs are supported by configuration. The CTT essentially determines the tunnel encapsulation used to transport each specific frame across the CRED. 4. Functional Description The RBridge Architecture is largely defined by RBridge behavior; the logical components are minimal, as outlined in Section 3. Gray Expires September, 2007 [Page 16] Internet-Draft RBridge Architecture March 2007 4.1. CRED Auto-configuration Cooperating RBridges self-organize to compose a single CRED system. Consider first a set of bridges on a single Ethernet link subnet (Figure 1). Here bridges are shown as 'b', hubs as 'h', and nodes as 'N'; bridges and hubs are numbered. Note that the figure does not distinguish between types of nodes, i.e., hosts and routers; both are end nodes at the link layer, and are otherwise indistinguishable to L2 forwarding devices. Bridges in this topology organize into a single spanning tree, as shown by double lines ('=', '||', and '//') in the figure. N N---b3---N | || | || N---h1--b4===b5==h2==b6 | // | || | // N || | // || N---b7====b8-----b9-----N | |\ | | \ N N N Figure 1 Conventionally bridged Ethernet link subnet It is useful to note that hubs are relatively transparent to bridges, both for traffic from nodes to bridges (h1) and for traffic between bridges (h2). Also note that the same hub can support traffic between bridges and from a host to a bridge (h2), but that the spanning tree is exclusively between bridges. Bridges are thus compatible with hubs, both as transits and ingress/egress. A CRED operates similarly, and can be viewed as a variant of the way bridges self-organize. Figure 2 shows the same topology where some of the bridges are replaced by RBridges (shown as 'r' in the figure). In this figure, stars ('*') represent the paths the RBridge is capable of utilizing, due to the use of link state routing. RBridges can tunnel directly to each other (r4- r5), or through hubs (h2) or bridges (b8). Note that the former b8-b9 path, which is b8-r9 in Figure 2 and had been disable by the hypothetical spanning tree in Figure 1, is now usable. Gray Expires September, 2007 [Page 17] Internet-Draft RBridge Architecture March 2007 N N---b3---N | || | || N---h1--r4***r5**h2**r6 * * | * * * N * * * * N---r7****b8*****r9-----N | |\ | | \ N N N Figure 2 RBridged Ethernet link subnet Every node in a CRED is considered to have a primary point of attachment to the CRED, as defined by the Designated RBridge. Each Ethernet link segment attached to a CRED has a single Designated RBridge; that RBridge is where all traffic that transits the CRED enters and exits. In Figure 2, it is easy to see that the nodes off of h1 must attach at r4; the nodes off of b3, however, attach at either r5 or r6, depending on which is the Designated RBridge. Without loss of generality, an RBridge topology can be reorganized (ignoring link length) such that all nodes, hubs, and bridges are arranged around the periphery, and all RBridges are considered directly connected by their tunnels (Figure 3). Note that this view ignores the ways in which hubs and bridges may serve both on the ingress/egress and for transit, hence this view is not useful for traffic analysis. Using this view, it is easy to distinguish between RBridge to RBridge traffic and other traffic on shared devices, such as h2 and b8, because RBridge to RBridge traffic content is hidden from non RBridge devices by the RBridge encapsulation. Gray Expires September, 2007 [Page 18] Internet-Draft RBridge Architecture March 2007 N N---b3---N | || | || | h2 | /| \ | / N \ | / \ N---h1--r4***r5******r6 * * * * * * * * * N---r7***********r9-----N \ /|\ \ / | \ \ / N N \ / \ / b8 | N Figure 3 Reorganized RBridge Ethernet link subnet 4.2. RBridge Peer Discovery Proper operation of the TRILL solution using RBridges depends on the existence of a mechanism for discovering peer RBridges and the RBridge topology. An accurate determination of RBridge topology is required in order to determine how traffic frames will flow in the topology and thus avoid the establishment of persistent loops in frame forwarding. The discovery mechanisms must use protocol messages which will be propagated throughout a LAN (or broadcast domain) until they are consumed by another RBridge. This must happen in order to ensure that RBridges in the same broadcast domain are discovered by their peers as required to allow for accurate determination of RBridge topology. These protocol messages should be distinguished in a manner that is consistent with the chosen RBridge routing protocol, or any other discovery mechanism used. It is very likely that peer discovery will actually be done as part of the RBridge routing protocol's peer discovery; however this is to be determined by specific RBridge protocol specification(s). Gray Expires September, 2007 [Page 19] Internet-Draft RBridge Architecture March 2007 An RBridge intercepts protocol messages that it recognizes as being of this type (peer discovery), performs any processing required and forwards these messages as required by the discovery protocol. For example, a receiving RBridge may first determine if it has seen this message before and insert itself in a list of RBridges traversed by this message prior to forwarding the message on at least all interfaces other than the one on which it was received. Note that forwarding the modified message on all interfaces in the example above is safe, if somewhat wasteful. RBridges must forward all other protocol messages in a manner consistent with L2 addressing and forwarding - as would be done by a typical 802.1D bridge. Handling of 802.1D BPDUs is as determined in section 4.8. 4.3. Tunneling RBridges pass encapsulated frame traffic to each other effectively using tunnels. These tunnels use an Ethernet link layer header, together with a shim header. Specifics of encapsulation are to be defined in appropriate protocol/encapsulation specifications. It is the combination of the encapsulation that distinguishes RBridge to RBridge traffic from other traffic. The link header includes source and destination addresses, which typically identify the ingress and egress RBridges. For incoming multicast and broadcast traffic, one of these addresses may represent the multicast group or broadcast address. Additionally, these addresses may be VLAN-specific, i.e., such that each ingress and egress address have per-VLAN addresses. The additional shim header is required to support loop mediation for traffic within the CRED; traffic loops in forwarding between RBridges and non-RBridge nodes, as well as across non-RBridge devices between RBridges, is limited by loop mediation and/or prevention mechanisms that are beyond the scope of this document (but may include a TTL-like mechanism, mechanisms to establish a loop free topology - such as STP/RSTP/MSTP - or both) on the applicable LAN links. The shim header and encapsulation: Gray Expires September, 2007 [Page 20] Internet-Draft RBridge Architecture March 2007 o must clearly identify the traffic as RBridge traffic - the outer Ethernet header may, for instance, use an Ethertype number unique to RBridges; o should also identify a specific (egress) RBridge - the shim header may, for example, include an identifier unique to the egress RBridge; o should include the RBridge transit route, a hopcount, or a timestamp to prevent indefinite looping of a frame. 4.4. RBridge General Operation Operations that apply to all RBridges include peer and topology discovery (which may include negotiation of RBridge identifiers), Designated RBridge election, link-state routing, SPF computation and advertising reach-ability for specific L2 (MAC Ethernet destination) addresses within a broadcast domain. In addition, all RBridges will compute RBridge Distribution Trees for delivery of (potentially VLAN scoped) broadcast, multicast and flooded frames to each peer RBridge. Setting up these trees early is important as there is otherwise no means for frame delivery across the CRED during the learning phase. Because it is very likely to be impossible (at an early stage) for RBridges to determine which RBridges are edge RBridges, it is preferable that each RBridge compute these trees for all RBridges as early as possible - even if some entries will not be used. The initial phase is the peer and topology discovery phase. This should continue for a sufficient amount of time to reduce the amount of re-negotiation (Designated RBridge and - possibly - identifiers) and re-computation that will be triggered by discovery of new peers. The timer values selected for delaying the next phase should take into account the time required for local STP and availability of segment connectivity between RBridge peers. The next phase is election of Designated RBridges for all shared access segments. This phase cannot complete before completion of peer and topology discovery. In parallel, RBridge routing protocol should begin the process of building the link-state information - assuming this was not done during the peer and topology discovery phase. Gray Expires September, 2007 [Page 21] Internet-Draft RBridge Architecture March 2007 At about this time, RBridges should establish RBridge Distribution Trees. Once RBridges have established RBridge Distribution Trees, the learning and forwarding phase may begin. In this phase, RBridges initially forward frames by flooding via RBridge Distribution Tree(s). Also during this phase, RBridges begin "learning" MAC address locations from local segments and propagating L2 reach- ability information via the RBridge routing protocol to all other RBridges. Gradually, the CFT will be built up for all RBridges, and fewer frames will require flooding via the Ingress RBridge Tree(s). ARP/ND optimization may occur during this phase as information learned from ARP/ND queries may be propagated across the CRED - potentially significantly reducing the impact of at least one source of broadcast traffic. The learning phase typically does not complete as new MAC attachment information continues to be learned and old information may be timed out and discarded. Consequently, the learning phase is also the operational phase. During the combined learning and operational phase, all RBridges maintain both RBridge Distribution Trees and a CFT. RBridges not elected as the Designated RBridge may be required to become one in the event that the DR goes off-line. 4.5. Ingress/Egress Operations Operation specific to edge RBridges involves RBridge learning, advertisement, encapsulation (at ingress RBridges) and decapsulation (at egress RBridges). As described elsewhere, RBridge learning is similar to typical bridge learning - i.e. - all RBridges listen promiscuously to L2 Frames on a local LAN segment and acquire location information associated with source MAC addresses in L2 frames they observe. By convention, a Designated RBridge election always occurs. In the degenerate case - where only one RBridge is connected to a specific Ethernet segment - obviously that RBridge will "win" the election and become the designated RBridge. With this convention, only the Designated RBridge performs RBridge learning for interface(s) connected to that segment. Gray Expires September, 2007 [Page 22] Internet-Draft RBridge Architecture March 2007 As each RBridge learns segment-local MAC source addresses, it creates an entry in its LPT that associates that MAC source address with the interface on which it was learned. Similarly - for ARP/ND optimization - IP-to-MAC association information may also be learned by snooping corresponding protocol messages. Protocol specifications may include either optional or required behaviors to support ARP/ND, or multicast, learning and distribution methods. Periodically, as determined by RBridge protocol specification, each RBridge advertises this learned information to its RBridge peers. These advertisements propagate to all edge RBridges (as potentially scoped by associated VLAN information for each advertisement). Each edge RBridge incorporates this information in the form of a CFT entry. RBridges also discover that they are an edge RBridge as a result of receiving un-encapsulated frames that require forwarding. If an RBridge is the Designated RBridge for a segment, and it has not previously learned that the MAC destination for a frame is local (this will be the case - for instance - for the very first frame it observes), then the RBridge would be required to forward (or flood) the frame via the CRED to all other RBridges (potentially within a VLAN scope). The RBridge in this case would flood the frame unless it has already created a unicast CFT entry for the frame's MAC destination address. If it has a corresponding CFT, then it would use that. This RBridge would be an ingress RBridge with respect to the frame being forwarded. The encapsulation used by this ingress RBridge would be determined by the CFT - if one exists - or the CFT-equivalent entry for the Ingress RBridge Tree. The encapsulation - as discussed elsewhere - should include (in the shim header) information to identify the egress RBridge (for example, the RBridge identifier negotiated previously during the peer and topology discovery phase). When the encapsulated frame arrives at egress RBridge(s), it is decapsulated and forwarded via the egress interface(s) onto the local segment. Gray Expires September, 2007 [Page 23] Internet-Draft RBridge Architecture March 2007 Note that an egress RBridge will be the Designated RBridge on the local segment accessed via its egress interface(s). If the received frame does not correspond to a learned MAC destination address at an egress interface, it will forward the frame on all interfaces for which it is either the designated - or only - RBridge. If the received frame does correspond to a learned MAC destination address at an egress interface, the RBridge will forward the frame via that interface only. 4.6. Transit Forwarding Operations There two models for transit forwarding within a CRED: unicast frame forwarding for known destinations, and everything else. The difference between the two is in how the encapsulation is determined. Exactly one of these models will be selected - in any instantiation of this architecture- for each of the following forwarding modes: o Unicast frame forwarding o Forwarding of non-unicast frames o Broadcast frame forwarding o Multicast frame forwarding o Frame flooding 4.6.1. Unicast In unicast forwarding, the shim header is specific to the egress RBridge and MAC destination in the outer Ethernet encapsulation is specific to the next hop RBridge. As the frame is prepared for transmission at each RBridge, the next hop MAC destination information is determined at that local RBridge using a corresponding CFT entry based on the "shim" header. 4.6.2. Broadcast, Multicast and Flooding Ingress RBridge Trees are used for forwarding of broadcast, multicast and unknown destination frames across the CRED. In a simple implementation, it is possible to use the CFT-RDT entries for all frames of these types. However, this approach results in potentially extreme inefficiencies in the multicast and unknown destination flooding cases. Gray Expires September, 2007 [Page 24] Internet-Draft RBridge Architecture March 2007 As a consequence, instantiations of this architecture should allow for local optimizations on a hop by hop basis. Examples of such optimizations are included in the sections below. 4.6.2.1. Broadcast The path followed in transit forwarding of broadcast frames will have been established through actions initiated by each RBridge (as any RBridge is eligible to subsequently become an ingress RBridge) in the process of computing CFT-RDT entries. Each RBridge assumes that it may be a transit as well as an ingress and egress RBridge and will establish forwarding information relative to itself and each of its peer RBridges, and stored in the CFT-RDT. CFT-RDT entries are computed at each RBridge for paths going toward all other RBridges - at least in cases where the RBridge performing CFT-RDT computations is on the shortest path. Forwarding information is in two forms: transit encapsulation information for interfaces over which the RBridge will forward a broadcast frame to one or more peer RBridges and a decapsulation indication for each interface over which the RBridge may egress frames from the CRED. In each case, the CFT-RDT includes some identification of the interface on which a frame is forwarded toward any specific egress RBridge for frames received from any specific ingress RBridge. Note that an interface over which an RBridge may egress frames is any interface for which the RBridge is a Designated RBridge. RBridges must not wait to determine that one (or more) non- RBridge Ethernet nodes is present in an interface before deciding to forward decapsulated broadcast frames on that interface. Forwarding information is selected for each broadcast frame received by any RBridge (based on identifying the ingress RBridge for the frame) for all corresponding CFT-RDT entries. Each RBridge is thus required to replicate one RBridge encapsulated broadcast frame for each interface that is determined from CFT-RDT entries corresponding to the frame's ingress RBridge. This includes decapsulated broadcast frames for each interface for which it is the designated RBridge. Note that frame replication and forwarding should be scoped by VLAN if VLAN support is provided. Also note that a Designated Gray Expires September, 2007 [Page 25] Internet-Draft RBridge Architecture March 2007 RBridge (DR) may be required to transmit a decapsulated frame on the interface on which it received the RBridge encapsulated frame. This approach for broadcast forwarding might be considered to add complexity because replication occurs at all RBridges along the ingress RBridge tree, potentially for both RBridge encapsulated and decapsulated broadcast frames. However, the replication process is similar to replication of broadcast traffic in 802.1D bridges with the exception that additional replication may be required at each interface for egress from the CRED. Note that the additional replication associated with CRED egress may be made to exactly conform to 802.1D bridge broadcast replication in implementations that model a CRED egress as a separate logical interface. Using this approach results in one and only one copy of the broadcast frame being delivered to each egress RBridge. 4.6.2.2. Multicast Multicast forwarding is reducible to broadcast forwarding in the simplest (default) case. However implementations may choose - using mechanisms that are out of scope for this document - to optimize multicast forwarding. In order for this to work effectively, however, support for awareness of multicast "interest" is required for all RBridges. Without optimization, multicast frames are injected by the ingress RBridge onto an RDT by - for instance - encapsulating the frame with a MAC destination multicast address, and forwarding it according to its local CFT-RDT. Again, without optimization, each RBridge along the path toward all egress RBridges will similarly forward the frame according to their local CFT-RDT. Using this approach results in one and only one copy of the multicast frame being delivered to appropriate egress RBridges. However, using this approach, multicast delivery is identical to broadcast delivery - hence very inefficient. In any optimization approach, RBridge encapsulated multicast frames will use either a broadcast or a group MAC destination address. In either case, the recognizably distinct destination addressing allows a frame forwarding decision to be made at each Gray Expires September, 2007 [Page 26] Internet-Draft RBridge Architecture March 2007 RBridge hop. RBridges may thus be able to take advantage of local knowledge of multicast distribution requirements to eliminate the forwarding requirement on interfaces for which there is no recipient interested in receiving frames associated with any specific group address. As stated earlier, in order for RBridges to be able to implement multicast optimization, distribution of learned multicast group "interest" information must be provided - and propagated - by all RBridges. Mechanisms for learning and propagating multicast group participation by RBridges is out of scope in this document but may be defined in RBridge protocol specification(s). Note that, because the multicast optimization would - in principle - further scope and reduce broadcast traffic, two things may be said: o It is not necessary that all implementations in a deployment implement the optimization (though all must support the data required to implement it in RBridge peers) in order for any local multicast optimization (consistent with the above description) to work; o Introduction of a multicast optimization will not result in potential forwarding loops where broadcast forwarding would not do so. In the simplest case, the ingress RBridge for a given multicast frame will re-use the MAC destination group address of a received multicast frame. However this may not be required as it is possible that the mechanisms specified to support multicast will require examination of the decapsulated MAC destination group address at each RBridge that implements the optimization. 4.6.2.3. Flooding Flooding is similarly reducible to broadcast forwarding in the simplest (default) case - with the exception that a frame being flooded across the CRED is typically a unicast frame for which no CFT exists at the ingress RBridge. This is not a minor distinction, however, because it impacts the way that addressing may be used to accomplish flooding within the CRED. An ingress RBridge that does not have a CFT entry for a received frame MAC destination address, will inject the frame onto the ingress RBridge Tree by - for instance - encapsulating the frame with a MAC destination broadcast address, and forwarding it Gray Expires September, 2007 [Page 27] Internet-Draft RBridge Architecture March 2007 according to its local CFT-RDT. Without optimization, each RBridge along the path toward all egress RBridges will similarly forward the frame according to their local CFT-RDT. Using this approach results in one and only one copy of the flooded frame being delivered to all egress RBridges. However implementations may choose to optimize flooding. A Flooding optimization will only work at any specific RBridge if that RBridge re-evaluates the original (decapsulated) unicast frame. Any flooding optimization would operate similarly to the multicast optimization described above, except that - instead of requiring local information about multicast distribution - each RBridge implementing the optimization will need only to lookup the MAC destination address of the original (decapsulated) frame in its local CFT. If an entry is found, the frame could then be forwarded only if the specific RBridge is on the shortest path between the originating ingress RBridge and the appropriate egress RBridge. This could be implemented - for example - as a specialized CFT-RDT entry. Note that, because the flooding optimization would - in principle - further scope and reduce flooded traffic, two things may be said: o It is not necessary that all implementations in a deployment support the optimization in order for any local flooding optimization (consistent with the above description) to work (hence such an optimization is optional); o Introduction of the flooding optimization will not result in potential forwarding loops where flooded forwarding would not do so. Because a forwarding decision can be made at each hop, it is possible to terminate flooding early if a CFT for the original MAC destination was in the process of being propagated when flooding for the frame was started. It is therefore possible to reduce the amount of flooding to some degree in this case. 4.7. Routing Protocol Operation The details of routing protocol operation can be determined once a specific routing protocol has been selected. These details would be defined in appropriate protocol specification(s). Gray Expires September, 2007 [Page 28] Internet-Draft RBridge Architecture March 2007 Protocol specifications should identify means for determining the content of the CFT, CFT-RDT and CTT. 4.8. Other Bridging and Ethernet Protocol Operations In defining this architecture, several interaction models have been considered for protocol interaction between RBridges and other L2 forwarding devices - in particular, 802.1D bridges. Whatever model we adopt for these interactions must allow for the possibility of other types of L2 forwarding devices. Hence, a minimal participation model is most likely to be successful over the long term, assuming that RBridges are used in a L2 topology that would be functional if RBridges were replaced by other types of L2 forwarding devices. Toward this end, RBridges - and the CRED as a whole - could (in theory) participate in Ethernet link protocols, notably the spanning tree protocol (STP) on the ingress/egress links using exactly one of the following interaction models: o Transparent Participation (Transparent-STP) o Active Participation (Participate-STP) o Blocking Participation (Block-STP) Only one of these variants would be supported by an instance of this architecture. All RBridges within a single CRED must use the same model for interacting with non-RBridge protocols. Furthermore, it is the explicit intent that only one of these models is ultimately supported - at least as a default mode of compliant implementations. This architecture assumes RBridges block STP. 4.8.1. Wiring Closet Problem There is at least one remaining issue with this assumption and that has been referred to as the "wiring closet problem." The essential problem is described in this subsection. Given this configuration of bridges in a wiring closet, and an RBridge core: -----> B-1 <----------------> RB-a <-----. | \ / > RBridge CORE | / -----> B-2 <----------------> RB-b <-----' Gray Expires September, 2007 [Page 29] Internet-Draft RBridge Architecture March 2007 The link between (802.1D) bridges B-1 and B-2 is meant to be disabled by STP. In the RBridge case, however, there is no indication (from STP) that this link is redundant. Moreover, in order to avoid breaking bridge learning, either RB-a or RB-b will be the DR and - as a result, only one of the links (B- 1<=>RB-a, B-2<=>RB-b) will get used. One solution to this problem is to include - as a configuration option, for instance - the ability to enable negotiation of (or use of a pre-defined, or configurable) pseudo-bridge identifier to be used in any of the variations of STP. One - (near) zero-configuration - option we've considered would be to use a well-known bridge identifier that each RBridge would use as a common pseudo-bridge identifier. Such an ID, used in combination with other STP configuration parameters, would most likely have to be guaranteed to win the root bridge election process in order to be a reasonable and useful default. However, because this architecture assumes RBridges block STP, participation in any form of STP is assumed to take place in an in-line, co-located bridge function. Such a bridge function is in addition to RBridge architectural functionality described in this document. Implementations may include such functionality and will very likely require some minimal configuration to turn it on, in vendor specific RBridge implementations. An example of a minimal configuration would be to assign a pseudo-bridge identifier to (the local in-line co-located bridge associated with) a specific RBridge port. For reasons of interoperability, specific protocol proposals to address the needs of this architecture may specify exactly how a co-located bridge will operate in this case (if such co-located bridge functionality is included in an implementation), as well as whether or not inclusion of such co-location is required. As a further note, one of the problems that should be addressed - assuming that this problem is to be resolved - is how to make certain the solution is robust against configuration error. In any solution that requires configuration of a pseudo-bridge ID that is common across a CRED, for example, it is possible to guard against configuration errors by using an election process (based on the root bridge election process) to determine which configured ID will be used by all RBridges in common - assuming that multiple pseudo-bridge IDs are inadvertently configured. Gray Expires September, 2007 [Page 30] Internet-Draft RBridge Architecture March 2007 Finally, note that there is a chicken-and-egg problem associated with RBridge participation in STP where RBridges may themselves be connected by spanning trees. 5. How RBridges Address the TRILL Problem Space The RBridge architecture addresses the following aspects of the requirements identified in reference [2] through the use of an IGP routing protocol and defined forwarding behaviors: o Inefficient Paths o Robustness to Link Interruption In addition, using a logical model of "separation of functions" this architecture allows specifications and implementations to address existing and developing Ethernet extensions and enhancements, and provides a background against which protocol specifications may address: concerns about convergence under dynamic network changes, and optimizations for VLAN, ARP/ND, Multicast, etc. 6. Conclusions This document discusses options considered and factors affecting any protocol specific choices that may be made in instantiating the TRILL architecture using RBridges. Specific architectural and protocol instantiations should take these into consideration. In particular, protocol, encapsulation and procedure specifications should allow for potential optimizations described in the architectural document to the maximum extent possible. Also, this document addresses considerations relative to interaction with existing technology and "future-proofing" solutions. For both simplicity in description, and robust long term implementation of the technology, this document recommends the use of clear distinction - at all possible points - of definitions, protocols, procedures, etc. from related (but not identical) specifications and interactions. In particular, this document recommends the use of a "collocation model" in addressing issues with combining RBridge, Router and 802.1D bridge behavior. Gray Expires September, 2007 [Page 31] Internet-Draft RBridge Architecture March 2007 7. Security Considerations As one stated requirement of this architecture is the need to be able to provide an L2 delivery mechanism that is potentially configuration free, the default operation mode for instances of this architecture should assume a trust model that does not require configuration of security information. This is - in fact - an identical trust model to that used by Ethernet devices in general. In consequence, the default mode does not require - but also does not preclude - the use of established security mechanisms associated with the existing protocols that may be extended or enhanced to satisfy this document's architectural definitions. In general, this architecture suggest the use of a link-state routing protocol - modified as required to support L2 reach- ability and link state between RBridges. Any mechanisms defined to support secure protocol exchanges between link-state routing peers may be extended to support this architecture as well. This architecture also suggests use of additional encapsulation mechanisms and - to the extent that any proposed mechanism may include (or be extended to include) secure transmission - it may be desirable to provide such (optional) extensions. To the extent possible, any extensions of protocol or encapsulation should allow for at least one mode of operation that doesn't require configuration - if necessary, for limited use in a physically secure deployment. 8. IANA Considerations This document has no direct IANA considerations. It does suggest, that protocols that instantiate the architecture use a shim header as a wrapper on the payload for RBridge to RBridge traffic, And this shim header may be identified by a new Ethertype in the tunneled Ethernet link header. This Ethertype, identified in an 802 header, would be allocated by the IEEE. 9. Acknowledgments The initial work for this document was largely done by Joe Touch, based on work he and Radia Perlman completed earlier. Subsequent changes are not to be blamed on them. Gray Expires September, 2007 [Page 32] Internet-Draft RBridge Architecture March 2007 In addition, the current text has been helped substantially by comments and suggestions from the TRILL working group, working group chairs, and from Ron Bonica, Stewart Bryant, Joel Halpern, Guillermo Ibanez and Russ White in particular. 10. References 10.1.Normative References None. 10.2.Informative References [1] Perlman, R., "RBridges: Transparent Routing", Proc. Infocom 2005, March 2004. [2] Touch, J., R. Perlman, (ed.) "Transparent Interconnection of Lots of Links (TRILL): Problem and Applicability Statement", work in progress, draft-touch-trill-prob- 00.txt, November, 2005. [3] Perlman, R., J. Touch, "RBridges: Base Protocol Specification", work in progress, draft-ietf-trill- rbridge-protocol-00.txt, January, 2006. [4] Postel, J., "INTERNET PROTOCOL", RFC 791, September, 1981. [5] 802.1D-2004 IEEE Standard for Local and Metropolitan Area Networks: Media Access Control (MAC) Bridges [6] Gray, E., (ed.) "TRILL Routing Requirements in Support of RBridges", work in progress, draft-ietf-trill-routing- reqs-00.txt, September, 2006 [7] Moy, J., "OSPF Version 2", RFC 2328, April, 1998. [8] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and Dual Environments", RFC 1195, December, 1990. [9] Coltun, R., D. Ferguson & J. Moy, "OSPF for IPv6", RFC 2740, December, 1999. [10] Plummer, D., "An Ethernet Address Resolution Protocol -- or -- Converting Network Protocol Addresses to 48.bit Ethernet Address for Transmission on Ethernet Hardware", RFC 826, November, 1982. Gray Expires September, 2007 [Page 33] Internet-Draft RBridge Architecture March 2007 Author's Addresses Editor: Eric Gray Ericsson 900 Chelmsford Street Lowell, MA, 01851 Phone: +1 (978) 275-7470 EMail: Eric.Gray@Ericsson.com Contributors: Joe Touch USC/ISI 4676 Admiralty Way Marina del Rey, CA 90292-6695, U.S.A. Phone: +1 (310) 448-9151 EMail: touch@isi.edu URL: http://www.isi.edu/touch Radia Perlman Sun Microsystems EMail: Radia.Perlman@sun.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. Gray Expires September, 2007 [Page 34] Internet-Draft RBridge Architecture March 2007 The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Gray Expires September, 2007 [Page 35]