Network Working Group X. Xu Internet-Draft K. Bi Intended status: Standards Track Huawei Expires: June 27, 2017 December 24, 2016 BGP Neighbor Autodiscovery draft-xu-idr-neighbor-autodiscovery-00 Abstract BGP has been used as an underlay routing protocol in many hyper-scale data centers. This document proposes a BGP neighbor autodiscovery mechanism which can be used to simplify the BGP deployment greatly. This mechanism is very useful for those hyper-scale data centers where BGP is used as an underlay routing protocol. 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 June 27, 2017. Copyright Notice Copyright (c) 2016 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. Xu & Bi Expires June 27, 2017 [Page 1] Internet-Draft December 2016 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. BGP Hello Message Format . . . . . . . . . . . . . . . . . . 3 4. Hello Message Procedure . . . . . . . . . . . . . . . . . . . 5 5. HELLO Message Error Handling . . . . . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 9.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction BGP has been used as an underlay routing protocol instead of IGP in many hyper-scale data centers [RFC7938]. Furthermore, there is an attempt to leverages BGP Link-State distribution and the Shortest Path First algorithm similar to Internal Gateway Protocols (IGPs) such as OSPF [I-D.keyupate-idr-bgp-spf]. In a word, there is a strong motivation to replace IGP by BGP in hyper-scale data centers. However, BGP is not good as IGP from the perspective of deployment automation and simplicity. For instance, the IP address and Autonomous System Number (ASN) of each BGP neighbor have to be manually configured on BGP routers although these BGP peers are directly connected. In addition, for those directly connected BGP routers, it's usually not ideal to establish BGP sessions over their directly connected interface addresses due to the following reasons: 1) it's not convient to do trouble-shooting; 2) the BGP update volume is unnecessarily increased when there are multiple physical links between them and those links couldn't be configured as a Link Aggregtion Group (LAG) due to whatever reason (e.g., diffferent link type or speed). As a result, it's more common that loopback interface addresses of those directly connected BGP peers are used for BGP session establishment. To make those loopback addresses of directly connected BGP peers reachable from one another, either static routes have to be configured or some kind of IGP has to be enabled. The former is not good from the automation perspective while the latter is in conflict with the original intention of using BGP as IGP. This draft specifies a BGP neighbor autodiscovery mechanism by borrowing some ideas from the Label Distribution Protocol (LDP) [RFC5036] . More specifically, directly connected BGP routers could Xu & Bi Expires June 27, 2017 [Page 2] Internet-Draft December 2016 automatically discovery the loopback address and the ASN of one other through the exchange of the to-be-defined BGP HELLO messages. The BGP session establishment process as defined in [RFC4271] is triggered once directly connected BGP neighbors are discovered from one another. Note that the BGP session should be established over the discovered loopback address of the BGP neighbor. In addition, to elimnate the need of configing static routes or enabling IGP for the loopback addresses, a certain type of routes towards the BGP neighbor's loopback addresses are dymatically created once the BGP neighbor has been discovered. The administritive distance of such type of routes MUST be smaller than their equivalents which are learnt via the normal BGP update messages . Otherwise, circular dependency problem would occur once these loopback addresses are advertised via the normal BGP update messages as well. 1.1. 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]. 2. Terminology This memo makes use of the terms defined in [RFC4271]. 3. BGP Hello Message Format To automatically discover directly connected BGP neighbors, a BGP router periodically sends BGP HELLO messages out those interfaces on which BGP neighbor autodiscovery are enabled. The BGP HELLO message is a new BGP message which has the same fixed-size BGP header as the exiting BGP messages. However, the HELLO message MUST sent as UDP packets addressed to the to-be-assigned BGP discovery port (179 is the suggested port value) for the "all routers on this subnet" group multicast address (i.e., 224.0.0.2 in the IPv4 case and FF02::2 in the IPv6 case. The IP source address is set to the address of the interface over which the message is sent out. In addition to the fixed-size BGP header, the HELLO message contains the following fields: Xu & Bi Expires June 27, 2017 [Page 3] Internet-Draft December 2016 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Hold Time | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLVs | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: BGP Hello Message Version: This 1-octet unsigned integer indicates the protocol version number of the message. The current BGP version number is 4. Hold Time: Hello hold timer in seconds. Hello Hold Time specifies the time the sending BGP peer will maintain its record of Hellos from the receiving BGP peer without receipt of another Hello. A pair of BGP peers negotiates the hold times they use for Hellos from each other. Each proposes a hold time. The hold time used is the minimum of the hold times proposed in their Hellos. A value of 0 means use the default 15 seconds. Message Length: This 2-octet unsigned integer specifies the length in octects of the ASN TLV, Connection Address TLV and other TLVs. TLVs: This field contains ASN TLV, Connection Address TLV and other TLVs. The ASN TLV format is show as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type=TBD2 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AS Number (2-octet or 4-octet) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: ASN TLV Type: TBD2. Length: Specifies the length of the Value field in octets. AS Number: This variable-length field indicates the 2-octet or 4-octet ASN of the sender. The Connection Address TLV format is shown as follows: Xu & Bi Expires June 27, 2017 [Page 4] Internet-Draft December 2016 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type=TBD3 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Connection Address (4-octet or 16-octet) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Connection Address TLV Type: TBD3 Length:Specifies the length of the Value field in octets. Connection Address: This variable-length field indicates the IPv4 or IPv6 loopback address which is used for establishing BGP sessions. 4. Hello Message Procedure A BGP peer receiving Hellos from another peer maintains a Hello adjacency corresponding to the Hellos. The peer maintains a hold timer with the Hello adjacency, which it restarts whenever it receives a Hello that matches the Hello adjacency. If the hold timer for a Hello adjacency expires the peer discards the Hello adjacency. We recommend that the interval between Hello transmissions be at most one third of the Hello hold time. A BGP session with a peer has one or more Hello adjacencies. A BGP session has multiple Hello adjacencies when a pair of BGP peers is connected by multiple links that have the same connection address; for example, multiple PPP links between a pair of routers. In this situation, the Hellos a BGP peer sends on each such link carry the same Connection Address. In addition, to elimnate the need of configing static routes or enabling IGP for the loopback addresses, a certain type of routes towards the BGP neighbor's loopback addresses (e.g., carried in the Connection Address TLV) are dymatically created once the BGP neighbor has been discovered. The administritive distance of such type of routes MUST be smaller than their equivalents which are learnt via the normal BGP update messages. Otherwise, circular dependency problem would occur once these loopback addresses are advertised via the normal BGP update messages as well. BGP uses the regular receipt of BGP Discovery Hellos to indicate a peer's intent to keep BGP session identified by the Hello. A BGP peer maintains a hold timer with each Hello adjacency that it Xu & Bi Expires June 27, 2017 [Page 5] Internet-Draft December 2016 restarts when it receives a Hello that matches the adjacency. If the timer expires without receipt of a matching Hello from the peer, BGP concludes that the peer no longer wishes to keep BGP session for that link or that the peer has failed. The BGP peer then deletes the Hello adjacency. When the last Hello adjacency for an BGP session is deleted, the BGP peer terminates the BGP session by sending a Notification message and closing the transport connection. 5. HELLO Message Error Handling TBD 6. Acknowledgements The authors would like to thank 7. IANA Considerations TBD. 8. Security Considerations TBD 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, . 9.2. Informative References [I-D.keyupate-idr-bgp-spf] Patel, K., Lindem, A., Zandi, S., and G. Velde, "Shortest Path Routing Extensions for BGP Protocol", draft-keyupate- idr-bgp-spf-02 (work in progress), December 2016. [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, October 2007, . Xu & Bi Expires June 27, 2017 [Page 6] Internet-Draft December 2016 [RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of BGP for Routing in Large-Scale Data Centers", RFC 7938, DOI 10.17487/RFC7938, August 2016, . Authors' Addresses Xiaohu Xu Huawei Email: xuxiaohu@huawei.com Kunyang Bi Huawei Email: bikunyang@huawei.com Xu & Bi Expires June 27, 2017 [Page 7]