TRILL Working Group Yizhou Li Internet Draft Weiguo Hao Intended status: Standards Track Huawei Technologies Radia Perlman Intel Labs Naveen Nimmu Broadcom S. Chatterjee IP Infusion Sunny Rajagopalan IBM Expires: July 2013 January 15, 2013 VLAN based Tree Selection for Multi-destination Frames draft-yizhou-trill-tree-selection-02.txt Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and 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 July 15, 2013. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. Li, et al. Expires July 15, 2013 [Page 1] Internet-Draft VLAN based Tree Selection January 2013 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. Abstract TRILL uses the distribution trees to deliver multi-destination frames. Multiple trees can be used by an ingress RBridge for different flow based on VLAN and/or multicast group. Different ingress RBridges may choose different distribution trees for the same VLAN and/or multicast group traffic. Distribution trees are normally pruned based on VLAN. For any RBridge RBn, if RBn has downstream receivers of VLAN x in a distribution tree t, there will be an entry of (t, x, port list) in the multicast forwarding table on RBn. If there are n trees and m VLANs, the multicast forwarding table size on RBn is typically n*m entries. The value of m is up to 4096 and n is the total number of distribution trees in the campus. If fine grained labeling is implemented or finer granularity filtering such as VLAN plus L2/L3 multicast address is used for pruning, the multicast forwarding table size further increases dramatically. TRILL multicast forwarding table size is limited by hardware and L3 multicasting may share the same table with it in hardware implementations. Therefore multicast table entry is a precious resource. This document specifies a VLAN based tree selection mechanism to reduce the TRILL multicast forwarding table size on RBridge. Table of Contents 1. Introduction ................................................ 3 1.1. Background ............................................. 3 1.2. Motivations ............................................ 4 2. Conventions used in this document............................ 6 3. VLAN based Tree Selection.................................... 6 3.1. Overview ............................................... 6 3.2. Sub-TLVs for the Router Capability TLV ................. 8 3.2.1. The Tree Identifier and VLANs Sub-TLV ............. 8 3.2.2. The Tree and VLANs Used Sub-TLV ................... 9 3.3. Detailed Processing..................................... 9 Li, et al. Expires July 15, 2013 [Page 2] Internet-Draft VLAN based Tree Selection January 2013 3.4. Failure Handling....................................... 10 3.5. Extensions ............................................ 11 4. Backward Compatibility...................................... 12 5. Aggregated Tree Nickname.................................... 13 6. Security Considerations..................................... 14 7. IANA Considerations ........................................ 14 8. References ................................................. 15 8.1. Normative References................................... 15 8.2. Informative References................................. 15 9. Acknowledgments ............................................ 15 1. Introduction 1.1. Background One or more distribution trees can be used to distribute multi- destination frames in a TRILL campus. The RBridge having the highest tree root priority announces the total number of trees that should be computed for the campus. It may also specify the ordered list of tree root nicknames that the other RBridges need to compute in the Tree Identifiers (TREE-RT-IDs) sub-TLV [RFC6326]. Every RBridge specifies the trees it wants to use in the Trees Used Identifiers (TREE-USE-IDs) sub-TLV and the VLAN it is interested in the Interested VLANs and Spanning Tree Roots (INT-VLAN) sub-TLV [RFC6326]. It is recommended that, by default, the ingress RBridge chooses the tree whose root is the closest[RFC6325]. Trees Used Identifiers sub-TLV is used to build the RPF table which is used for reverse path forwarding check; Interested VLANs sub-TLV is used for distribution tree pruning and the multicast forwarding table with pruning info is built based on that. Each distribution tree SHOULD be pruned per VLAN, eliminating branches that have no potential receivers downstream [RFC6325]. Further pruning based on L2/L3 multicast address is also possible. It is implementation dependant that how many trees to calculate, where the tree roots are located and which tree(s) to be used by an ingress RBridge. With the increasing demand to use TRILL in data center network, there are some features we can explore for multi- destination frames in the data center use case. In order to achieve non-blocking data forwarding, a fat tree structure is often used. Figure 1 shows a typical fat tree structure based data center network. RB1&RB2 are aggregation switches and RB11 to RB14 are access switches. It is a common practice to choose the tree roots to be at the aggregation switches for more efficient traffic transportation. All the ingress RBridges which are access switches have the same distance to all the tree roots. Li, et al. Expires July 15, 2013 [Page 3] Internet-Draft VLAN based Tree Selection January 2013 +-----+ +-----+ | RB1 | | RB2 | +-----+ +-----+ / | \\ / /|\ / | \ \ / / | \ / | \ / / | \-----+ / | \/ /\ | | / | /\/ \| | / /---+---/ /\ |\ | / / | / \ | \ | / / | / \ | \ | / / | / \ | \ | +-----+ +-----+ +-----+ +-----+ | RB11| | RB12| | RB13| | RB14| +-----+ +-----+ +-----+ +-----+ Figure 1 Fat Tree Structure based TRILL network 1.2. Motivations In the structure of figure 1, if we choose to put the tree root at RB1 and RB2, the ingress RBridge (e.g. RB11) would find more than one closest tree root (i.e. RB1 & RB2). Then an ingress RBridge has two options to select the tree root for multi-destination frames: choose one and only one as distribution tree root or use ECMP-like algorithm to balance the traffic among the multiple trees whose roots are at the same distance. For the former, single used tree per ingress RBridge, has the obvious problem of inefficient link usage. For example, if RB11 chooses the tree1 which is rooted at RB1 as the distribution tree, the link between RB11 and RB2 will never be used to ingress the multi-destination frame by RB11. For the latter, ECMP based tree selection results in a linear increase in multicast forwarding table size with the number of trees as explained in the next paragraph. A multicast forwarding table on an RBridge is normally used to map the key of (tree nickname + VLAN) to an index to a list of ports for multicast frame replication. The key used for mapping is simply the tree nickname when the RBridge does not prune the tree and the key could be (tree nickname + VLAN + L2/L3 multicast address) when the RBridge was programmed by control plane with L2/L3 multicast pruning information. For any RBridge RBn, for each VLAN x, if RBn is in a distribution tree t for VLAN x, there will be an entry of (t, x, port list) in the Li, et al. Expires July 15, 2013 [Page 4] Internet-Draft VLAN based Tree Selection January 2013 multicast forwarding table on RBn. Each entry contains a distinct combination of (tree nickname, VLAN) as the lookup key. If there are n such trees and m such VLANs, the multicast forwarding table size on RBn is n*m entries. If fine-grained label is used [TrillFGL] and/or finer pruning is used(e.g. VLAN + multicast group address is used for pruning), the value of m increases. In the larger scale data center, more trees would be necessary for better load balancing purpose and it results in the increasing of value n. In either case, the number of table entries n*m will increase dramatically. Figure 2 left table shows an example of the multicast forwarding table on RB11 in figure 1 topology with 2 distribution trees in campus. The number of entries is approximately 2 * 4K in this case. If 4 distribution trees are used in a TRILL campus and RBn has 4K VLANs with downstream receivers, it consumes 16K table entries. TRILL multicast forwarding table has a limited size in hardware implementation. The table entry is a precious resource. In some implementations, it shares with L3 IP multicast for a total of 16K or 8K table entries. Therefore we want to save the table size consumed as much as possible and at the same time to maintain the load balancing among trees. A straightforward way to alleviate the limited table entries problem is not to prune the distribution tree. However it can only be used in the restricted scenarios for the following reasons, - Unnecessary bandwidth waste for multi-destination frame. There is broadcast traffic in each VLAN, like ARP and unknown unicast. In addition, if there is huge L3 multicast traffic in some VLAN, no pruning may result in worse consequence of L3 user data unnecessarily flooded over the campus. The volume could be huge if certain application like IPTV is supported. Finer pruning like pruning based on multicast group may be desirable in this case. - Only useful at the pure transit nodes. Edge nodes always need to maintain the multicast forwarding table with the key of (tree nickname + VLAN) since the edge node needs to decide whether and how to replicate the frame to local access ports based on VLAN precisely. It is very likely that edge nodes are relatively low scale switches with the smaller shared table size, say 4K, available. - Security concerns. VLAN based traffic isolation is a basic requirement in some scenarios. No pruning may result in the unnecessary leak of the traffic. Misbehaved RBridge may take advantage of this. Li, et al. Expires July 15, 2013 [Page 5] Internet-Draft VLAN based Tree Selection January 2013 In addition to the multicast table size concern, some silicon does not support hashing based tree nickname selection at the ingress RBridge currently. VLAN based tree selection is used instead. Control plane of ingress RBridge maps the incoming VLAN x to a tree nickname t. Then data plane will always use tree t for VLAN x multi- destination frames. Though an ingress RB may choose multiple trees to be used for load sharing, it can use one and only one tree for single VLAN. If we make sure all ingress RBridges campus-wide send VLAN x multi-destination frames only using tree t, then there would be no need to store the multicast table entry with the key of (tree-other- than-t, x) on any RBridge. This document describes the control plane support for VLAN based tree selection mechanism to reduce the multicast forwarding table size. It consists with the silicon implementation mentioned in the previous paragraph. Here VLAN based tree selection is a general term which also includes finer granularity case, e.g. VLAN + L2/L3 multicast group based selection. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [RFC2119]. 3. VLAN based Tree Selection VLAN based tree selection can be used as a complementary distribution tree selection mechanism, especially when the multicast forwarding table size is a concern. 3.1. Overview The tree root with the highest priority announces the tree nicknames and the VLANs allowed on each tree. Such tree-VLAN correspondence announcement can be based on static configuration or some predefined algorithm. Ingress RBridge selects the tree-VLAN correspondence it wishes to use from the list announced by the highest priority tree root. It should not transmit VLAN x frame on tree y if the highest priority tree root does not say VLAN x is allowed on tree y. If we make sure one VLAN is allowed on one and only one tree, we can keep the number of multicast forwarding table entries on any RBridge fixed at 4K maximum (or up to 16M in case of fine grained label). Take Figure 1 as example, two trees rooted at RB1 and RB2 respectively. The highest priority tree root appoints the tree1 to carry VLAN 1-2000 and tree2 to carry VLAN 2001-4095. With such Li, et al. Expires July 15, 2013 [Page 6] Internet-Draft VLAN based Tree Selection January 2013 announcement by the highest priority tree root, every RBridge which understands the announcement will not send the VLAN 2001-4095 on tree1 or send the VLAN 1-2000 on tree2. Then no RBridge would need to store the entries for tree1/VLAN2001-4095 or tree2/VLAN1-2000. Figure 2 shows the multicast forwarding table on an RBridge before and after we perform the VLAN based tree selection. The number of entries is reduced by a factor f , f being the number of trees used in the campus. In this example, it is reduced from 2*4095 to 4095. This affects both transit nodes and edge nodes. Data plane does not change. +--------------+-----+---------+ +--------------+-----+---------+ |tree nickname |VLAN |port list| |tree nickname |VLAN |port list| +--------------+-----+---------+ +--------------+-----+---------+ | tree 1 | 1 | | | tree 1 | 1 | | +--------------+-----+---------+ +--------------+-----+---------+ | tree 1 | 2 | | | tree 1 | 2 | | +--------------+-----+---------+ +--------------+-----+---------+ | tree 1 | ... | | | tree 1 | ... | | +--------------+-----+---------+ +--------------+-----+---------+ | tree 1 | ... | | | tree 1 | 1999| | +--------------+-----+---------+ +--------------+-----+---------+ | tree 1 | ... | | | tree 1 | 2000| | +--------------+-----+---------+ +--------------+-----+---------+ | tree 1 | 4094| | | tree 2 | 2001| | +--------------+-----+---------+ +--------------+-----+---------+ | tree 1 | 4095| | | tree 2 | 2002| | +--------------+-----+---------+ +--------------+-----+---------+ | tree 2 | 1 | | | tree 2 | ... | | +--------------+-----+---------+ +--------------+-----+---------+ | tree 2 | 2 | | | tree 2 | 4094| | +--------------+-----+---------+ +--------------+-----+---------+ | tree 2 | ... | | | tree 2 | 4095| | +--------------+-----+---------+ +--------------+-----+---------+ | tree 2 | ... | | +--------------+-----+---------+ | tree 2 | ... | | +--------------+-----+---------+ | tree 2 | ... | | +--------------+-----+---------+ | tree 2 | 4094| | +--------------+-----+---------+ | tree 2 | 4095| | +--------------+-----+---------+ Figure 2 Multicast forwarding table before (left) & after (right) Li, et al. Expires July 15, 2013 [Page 7] Internet-Draft VLAN based Tree Selection January 2013 3.2. Sub-TLVs for the Router Capability TLV Two new sub-TLVs that can be carried in the Router Capability TLV for TRILL are defined below. They can be considered as analog of finer granularity version of the Tree Identifiers Sub-TLV and the Trees Used Identifiers Sub-TLV in [RFC6326]. 3.2.1. The Tree Identifier and VLANs Sub-TLV The tree identifiers and VLAN (TREE-VLANs) sub-TLV is used to announce the VLANs allowed on each tree by the IS that has the highest priority tree root. Multiple instances of this sub-TLV may be carried. Same tree nickname may occur in the multiple Tree-VLAN Records within the same or across multiple sub-TLVs. The sub-TLV format is as follows: +-+-+-+-+-+-+-+-+ | Type | (1 byte) +-+-+-+-+-+-+-+-+ | Length | (1 byte) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tree-VLAN Record (1) | (6 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ................. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tree-VLAN Record (N) | (6 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where each Tree-VLAN Record is of the form: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tree Nickname | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESV | Start.VLAN | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESV | End.VLAN | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Type: Router Capability sub-TLV type, set to 20 (TREE-VLANs). o Length: 6*n bytes, where there are n Tree-VLAN Records. Li, et al. Expires July 15, 2013 [Page 8] Internet-Draft VLAN based Tree Selection January 2013 o Tree Nickname: The nickname at which a distribution tree is rooted. o RESV: 4 bits that MUST be sent as zero and ignored on receipt. o Start.VLAN, End.VLAN: These fields are the VLAN IDs of the allowed VLAN range on the tree, inclusive. To specify a single VLAN, the VLAN's ID appears as both the start and end VLAN. 3.2.2. The Tree and VLANs Used Sub-TLV This sub-TLV has the same structure as the Tree Identifiers and VLAN sub-TLV (TREE-VLANs) specified in Section 3.2.2. The only difference is that its sub-TLV type is set to 21 (TREE-VLAN-USE), and the Tree- VLAN record listed are those the originating IS allows. 3.3. Detailed Processing The highest priority tree root includes all the necessary tree related sub-TLVs defined in [RFC6326] as usual and MAY optionally include the Tree Identifier and VLANs Sub-TLV (Tree-VLANs) in its LSP. The highest priority tree root may decide that each VLAN is only allowed on one and only one tree to maximize the saving in the multicast forwarding table size. Ingress RBridge that understands the Tree-VLANs Sub-TLV should select the tree-VLAN correspondences it wishes to use and put them in TREE- VLAN-USE sub-TLV. If there were multiple tree nicknames announced in Tree-VLANs Sub-TLV for a VLAN x, ingress RBridge must choose one of them. Ingress RB may choose the minimum distance root from them. How to make such choice is out of the scope of this document. It may be desirable to have some fixed algorithm to make sure all ingress RBs choose the same tree for VLAN x in this case. Any single VLAN that the ingress RBridge is interested in should be related to one and only one tree ID in TREE-VLAN-USE to minimize the multicast forwarding table size on other RBridges. When ingress RBridge tries to encapsulate a multi-destination frame for VLAN x, it should use the tree nickname that it selected previously in TREE-VLAN-USE for VLAN x. If RBridge RBn does not perform pruning at all, it builds the multicast forwarding table exactly same as that in [RFC6325]. If RBn prunes the distribution tree based on VLANs, RBn uses the information received in TREE-VLAN-USE sub-TLV to mark the set of Li, et al. Expires July 15, 2013 [Page 9] Internet-Draft VLAN based Tree Selection January 2013 VLANs reachable downstream for each adjacency and for each related tree. Logically, ingress RBridge that does not support VLAN based tree selection is equivalent to the one that supports it and announces all the combination pair of tree-id-used and interested-vlan as TREE- VLAN-USE. 3.4. Failure Handling Failure of a tree root: It is the responsibility of the highest priority tree root to inform others the change of the allowed tree- VLAN correspondence. When the highest priority tree root learns the root of tree t fails, it should re-assign the VLANs allowed on tree t to other trees or to a tree replacing the failed one. Failure of the highest priority tree root: It is recommended to pre- configure the second highest priority tree root with the proper knowledge of the tree-VLAN correspondence allowed when the highest priority tree root fails. The information announced by the second priority tree root would be stored by all RBridges but would not take effect unless the RBridge noticed the failure of the highest priority tree root. When the highest priority tree root fails, the original second priority tree root will become the highest priority tree root of the campus. When an RBridge notices the failure of the original highest priority tree root, it can immediately use the stored information announced by the original second priority tree root. It is recommended to pre-configure the tree-VLAN correspondence information on the second highest priority tree root same as that on the highest priority tree root for the trees other than the highest priority tree itself. This can make the change of multicast forwarding table minimum in case of the highest priority tree root failure. In some transient moment or misbehave of the highest priority tree root, an ingress RBridge may encounter the following scenarios: - No tree has been announced to allow VLAN x frames - An ingress RBridge is supposed to transmit VLAN x frames on tree t, but root of tree t is no longer reachable. For the second case, an ingress RBridge may choose another reachable tree root which allows VLAN x by the highest priority tree root announcement. If there is no such tree available, then it is same as the first case above. Then the ingress RBridge should be 'downgraded' to a conventional BRridge in [RFC6325]. A timer should be set to Li, et al. Expires July 15, 2013 [Page 10] Internet-Draft VLAN based Tree Selection January 2013 allow the temporary transient stage completion before the change of responsive tree or 'downgrade' takes effect. The value of timer should at least be set to the LSP flooding time in campus. 3.5. Extensions VLAN based tree selection can be easily extended to (VLAN+L2/L3 multicast group) based tree selection. For example, we can appoint multicast group 1 in VLAN 10 to tree1 and appoint group 2 in VLAN 10 to tree2 for better load sharing. New sub-TLVs are specified below for this purpose. +-+-+-+-+-+-+-+-+ |Type= | (1 byte) +-+-+-+-+-+-+-+-+ | Length | (1 byte) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tree Nickname | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESV | VLAN ID | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Num Group Recs | (1 byte) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | GROUP RECORDS (1) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | GROUP RECORDS (2) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ................. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | GROUP RECORDS (N) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where each group record is of the following form with k=4 for group IPv4 address and k=6 for group MAC address and k=16 for group IPv6 address: Li, et al. Expires July 15, 2013 [Page 11] Internet-Draft VLAN based Tree Selection January 2013 +-+-+-+-+-+-+-+-+ | Num of Sources| (1 byte) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Group Address (k bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source 1 Address (k bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source 2 Address (k bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ..... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source M Address (k bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4. Backward Compatibility RBridge should include the TREE-USE-IDs and INT-VLAN sub-TLVs when necessary as per RFC6325 no matter if it supports the new TREE-VLAN- USE sub-TLV specified by this draft. RBridge that understands new TREE-VLAN-USE sub-TLV sent from another RBridge RBn should use it to build the multicast forwarding table and ignore the TREE-USE-IDs and INT-VLAN sub-TLVs sent from the same RBridge. It should be noted that TREE-USE-IDs and INT-VLAN sub-TLVs are still useful for some purposes other than building multicast forwarding table, e.g. RPF table building, spanning tree root notification, etc. If the RBridge does not receive TREE-VLAN-USE sub- TLV from RBn, it uses the conventional way described in [RFC6325] to build the multicast forwarding table. For example, there are two distribution trees, tree1 & tree2 in the campus. RB1&RB2 are new RBridges which use the new sub-TLVs described in this document. RB3 is an old RBridge which is compatible with [RFC6325]. Assume RB2 is interested in VLAN 10&11 and RB3 is interested in VLAN 100&101. Hence RB1 receives ((tree1, VLAN10),(tree2, VLAN11)) as TREE-VLAN-USE sub-TLV and (tree1, tree2) as TREE-USE-IDs sub-TLV from RB2 on port x. And RB1 receives (tree1) as TREE-USE-IDs sub-TLV and no TREE-VLAN-USE sub-TLV from RB3 on port y. RB2 & RB3 announce their interested VLANs in INT-VLAN sub-TLV as usual. Then RB1 will build the entry of (tree1, VLAN10, port x) and (tree2, VLAN11, port x) based on RB2's LSP and mechanism specified in this document. RB1 also builds entry of (tree1, VLAN100, port y), (tree1, VLAN101, port y), (tree2, VLAN100, port y), (tree2, VLAN101, port y) based on RB3's LSP in conventional way. The multicast forwarding table on RB1 with merged entry would be like the following. Li, et al. Expires July 15, 2013 [Page 12] Internet-Draft VLAN based Tree Selection January 2013 +--------------+-----+---------+ |tree nickname |VLAN |port list| +--------------+-----+---------+ | tree 1 | 10 | x | +--------------+-----+---------+ | tree 1 | 100 | y | +--------------+-----+---------+ | tree 1 | 101 | y | +--------------+-----+---------+ | tree 2 | 11 | x | +--------------+-----+---------+ | tree 2 | 100 | y | +--------------+-----+---------+ | tree 2 | 101 | y | +--------------+-----+---------+ It is expected that the table is not shrunk as small as the one where every RB supports the new TREE-VLAN-USE sub-TLVs. The worst case in a hybrid campus is the number of entries equal to the number in current practice which does not support VLAN based tree selection. Such extreme case happens when the interested VLAN set from the new RBridges is a subset of the interested VLAN set from the old RBridges. VLAN based tree selection is compatibility with the current practice. Its effectiveness increases with more RBridge supporting this feature in the TRILL campus. 5. Aggregated Tree Nickname VLAN based tree selection needs control plane enhancement. This section illustrates another data plane mechanism to solve the multicast forwarding table size limitation problem. The idea is to aggregate the multicast forwarding table entries based on VLAN for all trees. If there are two trees, tree1 and tree2 in the campus, RBridge RBn may have two entries for VLAN x which are (tree1, VLAN-x, port-list-1) and (tree2, VLAN-x, port-list-2). After aggregation on tree nickname, the entry becomes (tree = wildcard/*, VLAN-x, port-list-1 UNION port-list-2). The multi-destination frames received by RBn for VLAN x will be replicated to both tree1 and tree2 outgoing ports. The next hop RBridge will perform the RPF checks. If a port is part of one tree but not the other, the next hop RBridge won't have an entry for the (source_RBridge, treeid) pointing to that incoming port in RPF checking table. Therefore next hop RBridge will drop those frames Li, et al. Expires July 15, 2013 [Page 13] Internet-Draft VLAN based Tree Selection January 2013 received on the wrong incoming ports. So this is a one-hop-delayed pruning. In some circumstances, the pruning may be delayed more than one hop. It happens when an RBridge located in multiple trees has the same incoming port for a RPF check. The following table gives some simple comparison on two approaches. +-------------+--------------------------+------------------------+ | |VLAN based tree selection | aggr tree nickname | +-------------+--------------------------+------------------------+ | | |depends.Hardware should | |data plane | no |be capable to support | |change req? | |tree nickname aggre | | | |searching | +-------------+--------------------------+------------------------+ |ctrl plane | Yes. Needs new sub-TLV | | |change req? | and new handlings | no | +-------------+--------------------------+------------------------+ | |inter-vlan multipathing. |allow intra-VLAN tree | |multipathing |Single VLAN uses single |based multipathing. | | |designated tree campus |Better load balancing | | |wide |within the VLAN | +-------------+--------------------------+------------------------+ |optimal | yes |slightly less than | |pruning? | |optimal in certain case | +-------------+--------------------------+------------------------+ The co-authors would like to seek comments and opinions on both approaches and their applicable scenarios. 6. Security Considerations This document does not change the general RBridge security considerations of the TRILL base protocol. See Section 6 of [RFC6325]. 7. IANA Considerations IANA is requested to allocate the new sub-TLV type code as specified in Section 3. Li, et al. Expires July 15, 2013 [Page 14] Internet-Draft VLAN based Tree Selection January 2013 8. References 8.1. Normative References [RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A. Ghanwani, "Routing Bridges (RBridges): Base Protocol Specification", RFC 6325, July 2011. [RFC6326] Eastlake, D., Banerjee, A., Dutt, D., Perlman, R., and A. Ghanwani, "TRILL Use of IS-IS", RFC 6326, July 2011. [6326bis] Eastlake, D. et.al., ''Transparent Interconnection of Lots of Links (TRILL) Use of IS-IS'', draft-eastlake-isis- rfc6326bis-07.txt, Work in Progress, December 2011. [RFC6439] Eastlake, D. et.al., ''RBridge: Appointed Forwarder'', RFC 6439, November 2011. 8.2. Informative References [RFC6165] Banerjee, A. and D. Ward, "Extensions to IS-IS for Layer-2 Systems", RFC 6165, April 2011. [RFC6327] Eastlake 3rd, D., Perlman, R., Ghanwani, A., Dutt, D., and V. Manral, "Routing Bridges (RBridges): Adjacency", RFC 6327, July 2011 [TrillFGL] Eastlake 3rd, D., Zhang, M., Agarwal, P., Dutt, D., and Perlman, R., ''TRILL: Fine-Grained Labeling'', draft-ietf- trill-fine-labeling-00.txt, December 2011 9. Acknowledgments Authors wish to thank David M Bond, Donald Eastlake, Liangliang Ma, Rakesh Kumar R for the valuable comments (names in alphabet order). This document was prepared using 2-Word-v2.0.template.dot. Li, et al. Expires July 15, 2013 [Page 15] Internet-Draft VLAN based Tree Selection January 2013 Authors' Addresses Yizhou Li Huawei Technologies 101 Software Avenue, Nanjing 210012 China Phone: +86-25-56625375 Email: liyizhou@huawei.com Weiguo Hao Huawei Technologies 101 Software Avenue, Nanjing 210012 China Phone: +86-25-56623144 Email: haoweiguo@huawei.com Radia Perlman Intel Labs 2200 Mission College Blvd. Santa Clara, CA 95054-1549 USA Phone: +1-408-765-8080 Email: Radia@alum.mit.edu Naveen Nimmu Broadcom 9th Floor, Building no 9, Raheja Mind space Hi-Tec City, Madhapur, Hyderabad - 500 081, INDIA Phone: +1-408-218-8893 Email: naveen@broadcom.com Li, et al. Expires July 15, 2013 [Page 16] Internet-Draft VLAN based Tree Selection January 2013 Somnath Chatterjee IP Infusion RMZ Centennial, Block D Doddanakundi Industrial Area, Kundanahalli Main Road,Mahadevapura Post, Bangalore - - 560 048 Karnataka, India Email: somnath.chatterjee01@gmail.com Sunny Rajagopalan IBM Email: sunny.rajagopalan@us.ibm.com Li, et al. Expires July 15, 2013 [Page 17]