BGP Neighbor Autodiscovery
draft-xu-idr-neighbor-autodiscovery-01
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| Authors | Xiaohu Xu , Kunyang Bi , Jeff Tantsura | ||
| Last updated | 2017-03-12 | ||
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draft-xu-idr-neighbor-autodiscovery-01
Network Working Group X. Xu
Internet-Draft K. Bi
Intended status: Standards Track Huawei
Expires: September 13, 2017 J. Tantsura
Individual
March 12, 2017
BGP Neighbor Autodiscovery
draft-xu-idr-neighbor-autodiscovery-01
Abstract
BGP has been used as the 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 the routing protocol.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 13, 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
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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
7.1. BGP Hello Message . . . . . . . . . . . . . . . . . . . . 6
7.2. TLVs of BGP Hello Message . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
BGP has been used as the 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
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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
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:
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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:
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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.
The Router ID TLV format is shown 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=TBD4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID (4-octet or 16-octet) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Router ID TLV
Type: TBD3
Length:Specifies the length of the Value field in octets and it's
set to 4 for the IPv4-address-formatted BGP Router ID.
Router ID: This variable-length field indicates the BGP router ID
which is used for performing the BGP-SPF algorithm as described in
[I-D.keyupate-idr-bgp-spf].
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.
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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
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
7.1. BGP Hello Message
This document requests IANA to allocate a new UDP port for BGP Hello
message.
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Value TLV Name Reference
----- ------------------------------------ -------------
Service Name: BGP-HELLO
Transport Protocol(s): UDP
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>.
Description: BGP Hello Message.
Reference: This document -- draft-xu-idr-neighbor-autodiscovery.
Port Number: TBD1 (179 is the suggested value) -- To be assigned by IANA.
7.2. TLVs of BGP Hello Message
This document requests IANA to create a new registry "TLVs of BGP
Hello Message" with the following registration procedure:
Registry Name: TLVs of BGP Hello Message.
Value TLV Name Reference
------- ------------------------------------------ -------------
0 Reserved This document
1 ASN This document
2 Connection Address This document
3 Router ID This document
4-65500 Unassigned
65501-65534 Experimental This document
65535 Reserved This document
8. Security Considerations
For security purposes, BGP speakers usually only accept TCP
connection attempts to port 179 from the specified BGP peers or those
within the configured address range. With the BGP auto-discovery
mechanism, it's configurable to enable or disable sending/receiving
BGP hello messages on the per-interface basis and BGP hello messages
are only exchanged between physically connected peers that are
trustworthy. Therefore, the BGP auto-discovery mechanism doesn't
introduce additional security risks associated with BGP.
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,
<http://www.rfc-editor.org/info/rfc2119>.
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[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,
<http://www.rfc-editor.org/info/rfc4271>.
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, <http://www.rfc-editor.org/info/rfc5036>.
[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,
<http://www.rfc-editor.org/info/rfc7938>.
Authors' Addresses
Xiaohu Xu
Huawei
Email: xuxiaohu@huawei.com
Kunyang Bi
Huawei
Email: bikunyang@huawei.com
Jeff Tantsura
Individual
Email: jefftant@gmail.com
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