Network Working Group Z. Chen Internet-Draft Huawei Intended status: Standards Track X. Xu Expires: September 6, 2018 Alibaba D. Cheng Huawei March 5, 2018 Avoiding Traffic Black-Holes for Route Aggregation in IS-IS draft-chen-isis-black-hole-avoid-02 Abstract When the Intermediate System to Intermediate System (IS-IS) routing protocol is adopted by a highly symmetric network such as the Leaf- Spine or Fat-Tree network, the Leaf nodes (e.g., Top of Rack switches in datacenters) are recommended to be prevented from receiving other nodes' explicit routes in order to achieve scalability. However, such a setup would cause traffic black-holes or suboptimal routing if link failure happens in the network. This document introduces INFINITE cost to IS-IS LSPs to solve this problem. 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 https://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 September 6, 2018. Chen, et al. Expires September 6, 2018 [Page 1] Internet-Draft IS-IS Black-Hole Avoiding March 2018 Copyright Notice Copyright (c) 2018 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 (https://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. Problem Description . . . . . . . . . . . . . . . . . . . . . 3 3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction When running the Intermediate System to Intermediate System (IS-IS) routing protocol in a highly symmetric network such as the Leaf-Spine or Fat-Tree network, the Leaf nodes (e.g., Top of Rack switches in datacenters) are recommended to be prevented from receiving other nodes' explicit routes in order to achieve scalability, as proposed in [IS-IS-SL-Extension], [IS-IS-Overhead-Reduction], [RIFT], and [OpenFabric]. In particular, each Leaf node SHOULD simply maintain a default (or aggregated) route (e.g., 0.0.0.0/0) in its routing table, of which the next hop SHOULD be an Equal Cost Multi Path (ECMP) group including all Spines nodes that the Leaf node connects to. However, such a setup would cause traffic black-holes or suboptimal routing if link failure happens in the network, since the Leaf nodes are not aware of any topology information. To solve this problem, this document introduces INFINITE cost to IS- IS LSPs. When link failure happens between a Spine node and a Leaf node, the Spine node SHOULD advertise all prefixes attached to the Leaf node, whose costs SHOULD be set to be INFINITE, to every other Leaf node it connects to. On receiving the prefixes (with INFINITE Chen, et al. Expires September 6, 2018 [Page 2] Internet-Draft IS-IS Black-Hole Avoiding March 2018 cost), each Leaf node SHOULD add the prefixes to its routing table, thus avoiding traffic black-holes and suboptimal routing. 2. Problem Description This section illustrates why link failure would cause traffic black- hole or suboptimal routing when Leaf nodes only maintain default (or aggregated) routes. +--------+ +--------+ +--------+ | Spine1 | | Spine2 | | Spine3 | +-+-+-+-++ +-+-+-+-++ +-+-+-+-++ +------+ | | | | | | | | | | | | +------|-|-|-------------+ | | | | | | X | | +----|-|-|---------------|-|-|-------------+ | | X | | | | | | +------+ | | | | X | | | | | | | +------|-|---------------+ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +-------+ +-----+ | | | | | | | | | +---------|-------------+ | | | | | | | | | +---------+ | | | | | | | | +--------|-|----------------|-|-----------+ | | | | | | +----------|-|--------------+ | | | | | | | | +----------+ | | | | | | | | +-+-+-+-+ +-+-+-+-+ +-+-+-+-+ +-+-+-+-+ | Leaf1 | | Leaf2 | | Leaf3 | | Leaf4 | +-------+ +-------+ +-------+ +-------+ | | --- --- prefixA prefixB Figure 1: Topology Example Figure 1 shows a Spine-Leaf topology example where Leaf1 to Leaf4 are connected to Spine1 to Spine3, and prefixA and prefixB are attached to Leaf4. To achieve scalability, as proposed in [IS-IS-SL- Extension], [IS-IS-Overhead-Reduction], [RIFT], and [OpenFabric], Leaf1 to Leaf4 SHOULD NOT receive explict routes from each other nor the Spine nodes. Instead, each of them maintains a default (or aggregated) route (e.g., 0.0.0.0/0) in the routing table, of which the next hop is an ECMP group including Spine1, Spine2, and Spine3. Flows from one Leaf node to another are shared among Spine1, Spine2, and Spine3 based on the well known 5-tuple hashing. However, such a setup would cause traffic black-hole or suboptimal routing when link failure happens in the network. For example, if Chen, et al. Expires September 6, 2018 [Page 3] Internet-Draft IS-IS Black-Hole Avoiding March 2018 the link between Spine3 and Leaf4 is broken, Leaf1, Leaf2, and Leaf3 could not get aware of the failure. As a result, these Leaf nodes will still send a portion of traffic destined for prefixA or prefixB toward Spine3, which makes the traffic be discarded at Spine3, causing traffic black-hole. On the other hand, if there are a set of links or a higher tier of switches interconnecting Spine1, Spine2, and Spine3, the traffic will be steered to other spine nodes or the higher-tier switches by Spine3, causing suboptimal routing. Therefore, this document introduces INFINITE cost to IS-IS LSPs to solve this problem. 3. Solution This document introduces the INFINITE cost to IS-IS LSPs, whose value is to be determined. When link failure happens between a Spine node and a Leaf node, the Spine node SHOULD 1) encode all prefixes attached to the Leaf node into the IP Reachability TLV, 2) set the cost of the prefixes to be INFINITE, 3) append the IP Reachability TLV to the IS-IS LSP, and 4) send the LSP to every other Leaf node it connects to. When a Leaf node receives the prefixes (with INFINITE cost) advertised by a Spine node, it SHOULD install each of the prefixes into its routing table, of which the next hop SHOULD be set an ECMP group including all Spine nodes it connects to except the one who advertises the prefix. For example, if the link between Spine3 and Leaf4 in Figure 1 is broken, Spine3 SHOULD advertise prefixA and prefixB to Leaf1, Leaf2, and Leaf3, by sending them an IS-IS LSP containing the IP Reachability TLV. The cost of prefixA and prefixB SHOULD be set INFINITE. On receiving the LSP, Leaf1, Leaf2, and Leaf3 SHOULD install prefixA and prefixB into their routing tables, and the next hop of prefixA or prefixB SHOULD be set an ECMP group including Spine1 and Spine2. For instance, the routing table of Leaf1 before and after the link failure is shown in Figure 2 and Figure 3, respectively. Note that the mechanism described above could achieve minimal signaling latency, which helps to avoid black-hole or suboptimal routing rapidly when link failure happens. Chen, et al. Expires September 6, 2018 [Page 4] Internet-Draft IS-IS Black-Hole Avoiding March 2018 +-----------+-----+---+----+-----+-------+--------------+ |Destination|Proto|Pre|Cost|Flags|NextHop|Interface | +-----------+-----+---+----+-----+-------+--------------+ |0.0.0.0/0 |ISIS |15 |20 |D |Spine1 |Ethernet0/0/0 | | |ISIS |15 |20 |D |Spine2 |Ethernet0/0/1 | | |ISIS |15 |20 |D |Spine3 |Ethernet0/0/2 | +-----------+-----+---+----+-----+-------+--------------+ Figure 2: Routing Table of Leaf1 before link failure +-----------+-----+---+----+-----+-------+--------------+ |Destination|Proto|Pre|Cost|Flags|NextHop|Interface | +-----------+-----+---+----+-----+-------+--------------+ |0.0.0.0/0 |ISIS |15 |20 |D |Spine1 |Ethernet0/0/0 | | |ISIS |15 |20 |D |Spine2 |Ethernet0/0/1 | | |ISIS |15 |20 |D |Spine3 |Ethernet0/0/2 | +-----------+-----+---+----+-----+-------+--------------+ |prefixA |ISIS |15 |20 |D |Spine1 |Ethernet0/0/0 | | |ISIS |15 |20 |D |Spine2 |Ethernet0/0/1 | +-----------+-----+---+----+-----+-------+--------------+ |prefixB |ISIS |15 |20 |D |Spine1 |Ethernet0/0/0 | | |ISIS |15 |20 |D |Spine2 |Ethernet0/0/1 | +-----------+-----+---+----+-----+-------+--------------+ Figure 3: Routing Table of Leaf1 after link failure 4. IANA Considerations TBD. 5. Security Considerations TBD. 6. Acknowledgements TBD. 7. References [IS-IS-Overhead-Reduction] Chen, Z., Xu, X., and D. Cheng, "Overheads Reduction for IS-IS Enabled Spine-Leaf Networks", draft-chen-isis-sl- overheads-reduction-03 (work in progress) , March 2018. Chen, et al. Expires September 6, 2018 [Page 5] Internet-Draft IS-IS Black-Hole Avoiding March 2018 [IS-IS-SL-Extension] Shen, N., Ginsberg, L., and S. Thyamagundalu, "IS-IS Routing for Spine-Leaf Topology", draft-shen-isis-spine- leaf-ext-05 (work in progress) , January 2018. [OpenFabric] White, R. and S. Zandi, "IS-IS Support for Openfabric", draft-white-openfabric-05 (work in progress) , January 2018. [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, . [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305 , October 2008. [RIFT] Przygienda, T., Sharma, A., Drake, J., and A. Atlas, "RIFT: Routing in Fat Trees", draft-przygienda-rift-05 (work in progress) , March 2018. Authors' Addresses Zhe Chen Huawei No. 156 Beiqing Rd Beijing 100095 China Email: chenzhe17@huawei.com Xiaohu Xu Alibaba Email: xiaohu.xxh@alibaba-inc.com Dean Cheng Huawei Email: dean.cheng@huawei.com Chen, et al. Expires September 6, 2018 [Page 6]