Network Working Group Z. Chen Internet-Draft X. Xu Intended status: Standards Track Huawei Technologies Expires: July 10, 2017 January 6, 2017 Overheads Reduction for IS-IS Enabled Spine-Leaf Networks draft-chen-isis-sl-overheads-reduction-00 Abstract When a Spine-Leaf topology adopts the Intermediate System to Intermediate System (IS-IS) routing protocol, the Leaf node receives Link State Packets (LSPs) from all the other nodes thus having the entire routing information of the topology. This is usually considered unnecessary and costly. This document describes a solution to this problem by assigning different area identifiers (AIDs) to the Leaf nodes. The solution requires that an IS-IS router SHOULD check a Level-1 LSP's AIDs before it advertises the LSP to its neighbor. Requirements Language 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]. 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). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on July 10, 2017. Chen & Xu Expires July 10, 2017 [Page 1] Internet-Draft IS-IS Spine-Leaf Overheads Reduction January 2017 Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Solution Description . . . . . . . . . . . . . . . . . . . . 3 2.1. Area ID Assignment . . . . . . . . . . . . . . . . . . . 3 2.2. Area ID Checking . . . . . . . . . . . . . . . . . . . . 5 2.3. Default Route Advertising . . . . . . . . . . . . . . . . 6 3. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 7 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 7. Normative References . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction Spine-Leaf topology (a.k.a., CLOS topology) is widely used in today's datacenter and campus networks. When the Spine-Leaf topology runs the Intermediate System to Intermediate System (IS-IS) routing protocol, each Leaf node will receive Link State Packets (LSPs) from all the other nodes and have the entire routing information of the topology. This is usually considered to be unnecessary and costly because the Leaf node only needs to know its default gateways (i.e., the Spine nodes it connects to), and the LSPs generated by the other Leaf nodes benefit nothing for it to forward traffic. To avoid Leaf nodes from learning the unnecessary LSPs from one another, [IS-IS-SL-Extension] proposes a new TLV of the IS-IS Hello (IIH) PDU to differentiate Spine/Leaf nodes and LSPs generated by Leaf nodes will be blocked at Spine nodes. Additionally, each Leaf node sets the Spine nodes it connects to as its default gateways. Chen & Xu Expires July 10, 2017 [Page 2] Internet-Draft IS-IS Spine-Leaf Overheads Reduction January 2017 This document describes another solution to this problem, which needs not to extend the IS-IS messages. In particular, it requires that each Leaf node SHOULD be assigned with a unique area identifier (AID) and IS-IS L1/L2 routers MUST NOT advertise Level-1 LSPs of a given area to Level-1 routers within another area. This prevents Leaf nodes from receiving routing information from one another, and lets the Leaf node set the Spine nodes as its default gateways. 2. Solution Description 2.1. Area ID Assignment +------------+ +------------+ | Spine-A | 10.10.10.0/24 | Spine-B | | L1/L2 +----------------------+ L1/L2 | | Area10/20 | .1 .2 | Area10/20 | +---+--+-----+ +---+----+---+ .1 | | .1 .2 | | .1 | | 10.10.40.0/24 | | | | +-----------------------------+ | 10.10.20.0/24 | | | | 10.10.30.0/24 | +--|-------------------------------+ | | | 10.10.50.0/24 | | .2 | | .1 .2 | | .2 +---+-----+--+ +-----+--+---+ | Leaf-A | | Leaf-B | | L1 | | L1 | | Area10 | | Area20 | +-----+------+ +-----+------+ | | | | ------+------- ------+------- 192.168.10.0/24 192.168.20.0/24 Figure 1: Topology Example This section describes how to assign AIDs in the Spine-Leaf topology, and illustrates why IS-IS routers SHOULD check the AIDs before advertising Level-1 LSPs. As shown in Figure 1, there are two Spine nodes (i.e., Spine-A and Spine-B) and two Leaf nodes (i.e., Leaf-A and Leaf-B). The System IDs of Spine-A, Spine-B, Leaf-A, and Leaf-B are 1111.1111.1111.1111.00 to 4444.4444.4444.00, respectively. To prevent a Leaf node from learning the routing information of the other Leaf nodes, the following configurations are required: Chen & Xu Expires July 10, 2017 [Page 3] Internet-Draft IS-IS Spine-Leaf Overheads Reduction January 2017 a. Leaf nodes SHOULD be configured as L1 routers and each of them SHOULD be assigned a unique AID. b. Spine nodes SHOULD be configured as L1/L2 routers and SHOULD be assigned multiple AIDs with each being that of a given Leaf node connected to it. As a result, Leaf-A and Leaf-B in Figure 1 are configured as L1 routers and are assigned AID 10 and AID 20, respectively. Spine-A and Spine-B are configured as L1/L2 routers and are assigned both AID 10 and AID 20. Level-1 Link State Database (Spine-A): +--------------------+----------+--------+--------+------+--------+-----+ |LSPID |Seq Num |Checksum|Holdtime|Length|ATT/P/OL|Area | +--------------------+----------+--------+--------+------+--------+-----+ |1111.1111.1111.00-00|0x0000006c|0x540b |743 |124 |0/0/0 |10/20| +--------------------+----------+--------+--------+------+--------+-----+ |2222.2222.2222.00-00|0x0000006d|0x933b |1068 |124 |0/0/0 |10/20| +--------------------+----------+--------+--------+------+--------+-----+ |3333.3333.3333.00-00|0x0000006b|0x1815 |402 |122 |0/0/0 |10 | +--------------------+----------+--------+--------+------+--------+-----+ |4444.4444.4444.00-00|0x0000006a|0xf543 |431 |122 |0/0/0 |20 | +--------------------+----------+--------+--------+------+--------+-----+ Level-2 Link State Database (Spine-A): +--------------------+----------+--------+--------+------+--------+-----+ |LSPID |Seq Num |Checksum|Holdtime|Length|ATT/P/OL|Area | +--------------------+----------+--------+--------+------+--------+-----+ |1111.1111.1111.00-00|0x0000006f|0x682f |743 |150 |0/0/0 |10/20| +--------------------+----------+--------+--------+------+--------+-----+ |2222.2222.2222.00-00|0x00000063|0x30eb |1068 |150 |0/0/0 |10/20| +--------------------+----------+--------+--------+------+--------+-----+ Figure 2: Link State Database of Spine-A Under such configurations, Leaf-A will still receives Leaf-B's LSPs (and vice versa) even though they are in different areas. This is because of the IS-IS definition that all routers in a specific area SHOULD share the same Level-1 Link State Database (LSDB). The LSDB of Spine-A is shown in Figure 2. In particular, since Spine-A and Leaf-B are both in area 20, Spine-A will receive the LSP 4444.4444.4444.00-00 from Leaf-B and store the LSP into its Level-1 LSDB. On the other hand, since Spine-A and Leaf-A are both in area 10, Spine-A will advertise the LSP 4444.4444.4444.00-00 to Leaf-A although Leaf-A and Leaf-B (generator of the LSP) are in different Chen & Xu Expires July 10, 2017 [Page 4] Internet-Draft IS-IS Spine-Leaf Overheads Reduction January 2017 areas. As a result, Leaf-A will install the route 192.168.20.0/24 into its routing table (Figure 3), even though it is an external area route. Leaf-A Routing Table: +---------------+-------+---+----+-----+----------+--------------+ |Destination |Proto |Pre|Cost|Flags|NextHop |Interface | +---------------+-------+---+----+-----+----------+--------------+ |10.10.10.0/24 |ISIS-L1|15 |20 |D |10.10.20.1|Ethernet0/0/0 | | |ISIS-L1|15 |20 |D |10.10.40.2|Ethernet0/0/1 | +---------------+-------+---+----+-----+----------+--------------+ |10.10.20.0/24 |Direct |0 |0 |D |127.0.0.1 |Ethernet0/0/0 | +---------------+-------+---+----+-----+----------+--------------+ |10.10.30.0/24 |ISIS-L1|15 |20 |D |10.10.40.2|Ethernet0/0/1 | +---------------+-------+---+----+-----+----------+--------------+ |10.10.40.0/24 |Direct |0 |0 |D |127.0.0.1 |Ethernet0/0/1 | +---------------+-------+---+----+-----+----------+--------------+ |10.10.50.0/24 |ISIS-L1|15 |20 |D |10.10.20.1|Ethernet0/0/0 | +---------------+-------+---+----+-----+----------+--------------+ |192.168.10.0/24|Direct |0 |0 |D |127.0.0.1 |GEthernet0/0/0| +---------------+-------+---+----+-----+----------+--------------+ |192.168.20.0/24|ISIS-L1|15 |30 |D |10.10.20.1|Ethernet0/0/0 | | |ISIS-L1|15 |30 |D |10.10.40.2|Ethernet0/0/1 | +---------------+-------+---+----+-----+----------+--------------+ |127.0.0.0/8 |Direct |0 |0 |D |127.0.0.1 |InLoopBack0 | +---------------+-------+---+----+-----+----------+--------------+ |0.0.0.0/0 |ISIS-L1|15 |10 |D |10.10.20.1|Ethernet0/0/0 | | |ISIS-L1|15 |10 |D |10.10.40.2|Ethernet0/0/1 | +---------------+-------+---+----+-----+----------+--------------+ Figure 3: Routing Table of Leaf-A Therefore, to avoid Level-1 LSPs of one area from being flooded into another area, an AID checking mechanism (see Section 2.2) is needed. 2.2. Area ID Checking Before an IS-IS router advertises a Level-1 LSP to a Level-1 neighbor, it SHOULD compare the AIDs associated with the LSP and the AIDs associated with the neighbor. If they have at least one AID in common, the router SHOULD advertise the LSP to the neighbor. Otherwise, the router MUST NOT advertise the LSP to the neighbor. For instance, as shown in Figure 1, before Spine-A advertises the LSP 1111.1111.1111.00-00 to Leaf-A, it compares the LSP's AIDs (i.e., 10 and 20) with Leaf-A's AID (i.e., 10). Since they have an AID in common that is AID 10, Spine-A SHOULD advertise the LSP to Leaf-A. Chen & Xu Expires July 10, 2017 [Page 5] Internet-Draft IS-IS Spine-Leaf Overheads Reduction January 2017 On the other hand, before Spine-A advertises the LSP 4444.4444.4444.00-00 to Leaf-A, it checks their AIDs and finds that they have no AID in common. So Spine-A MUST NOT advertise the LSP to Leaf-A. As a result, Leaf-A would not learn the routing information of Leaf-B, as shown in Figure 4. Leaf-A Routing Table: +---------------+-------+---+----+-----+----------+--------------+ |Destination |Proto |Pre|Cost|Flags|NextHop |Interface | +---------------+-------+---+----+-----+----------+--------------+ |10.10.10.0/24 |ISIS-L1|15 |20 |D |10.10.20.1|Ethernet0/0/0 | | |ISIS-L1|15 |20 |D |10.10.40.2|Ethernet0/0/1 | +---------------+-------+---+----+-----+----------+--------------+ |10.10.20.0/24 |Direct |0 |0 |D |127.0.0.1 |Ethernet0/0/0 | +---------------+-------+---+----+-----+----------+--------------+ |10.10.30.0/24 |ISIS-L1|15 |20 |D |10.10.40.2|Ethernet0/0/1 | +---------------+-------+---+----+-----+----------+--------------+ |10.10.40.0/24 |Direct |0 |0 |D |127.0.0.1 |Ethernet0/0/1 | +---------------+-------+---+----+-----+----------+--------------+ |10.10.50.0/24 |ISIS-L1|15 |20 |D |10.10.20.1|Ethernet0/0/0 | +---------------+-------+---+----+-----+----------+--------------+ |192.168.10.0/24|Direct |0 |0 |D |127.0.0.1 |GEthernet0/0/0| +---------------+-------+---+----+-----+----------+--------------+ |127.0.0.0/8 |Direct |0 |0 |D |127.0.0.1 |InLoopBack0 | +---------------+-------+---+----+-----+----------+--------------+ |0.0.0.0/0 |ISIS-L1|15 |10 |D |10.10.20.1|Ethernet0/0/0 | | |ISIS-L1|15 |10 |D |10.10.40.2|Ethernet0/0/1 | +---------------+-------+---+----+-----+----------+--------------+ Figure 4: Routing Table of Leaf-A 2.3. Default Route Advertising As defined in [RFC 1195], a L1/L2 router will indicate in its L1 LSPs that it is "attached" by setting the ATT bits. Therefore, each Leaf node in the example will set the Spine nodes as its default gateways and install the corresponding default routes into its routing table, as shown in Figure 4. However, a specific IS-IS implementation in this case may not let the L1/L2 router set the ATT bits, because it may speculate that the L1/ L2 router has lost connectivity to the Level-2 backbone. To solve this problem, operators can manually configure the L1/L2 router to advertise a default route. Chen & Xu Expires July 10, 2017 [Page 6] Internet-Draft IS-IS Spine-Leaf Overheads Reduction January 2017 3. Discussions The AID checking mechanism described in this document will put little effect on the current usage of the IS-IS protocol because of two reasons: a. In usual cases, an IS-IS router is assigned no more than one AID. Therefore no LSP will be blocked and the IS-IS protocol runs as normal. b. An IS-IS router is assigned more than one AIDs only when 1) it is desirable to change the AID of an area, 2) to merge two areas into one area, or 3) to partition an area into two areas. Apparently, the AID checking mechanism does not impact these operations. 4. IANA Considerations TBD. 5. Security Considerations TBD. 6. Acknowledgements TBD. 7. Normative References [IS-IS-SL-Extension] Shen, N. and S. Thyamagundalu, "IS-IS Routing for Spine- Leaf Topology", draft-shen-isis-spine-leaf-ext-02 (work in progress) , October 2016. [RFC1195] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and Dual Environments", RFC 1195 , December 1990. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Authors' Addresses Chen & Xu Expires July 10, 2017 [Page 7] Internet-Draft IS-IS Spine-Leaf Overheads Reduction January 2017 Zhe Chen Huawei Technologies No. 156 Beiqing Rd Beijing 100095 China Email: chenzhe17@huawei.com Xiaohu Xu Huawei Technologies No. 156 Beiqing Rd Beijing 100095 China Email: xuxiaohu@huawei.com Chen & Xu Expires July 10, 2017 [Page 8]