Internet DRAFT - draft-kumar-idr-link-local-nexthop
draft-kumar-idr-link-local-nexthop
Network Working Group V. Kumar
Internet-Draft Cumulus Networks
Intended status: Standards Track P. Mohapatra
Expires: May 17, 2015 Sproute Networks
D. Dutt
Cumulus Networks
M. Valentine
Goldman Sachs
November 13, 2014
BGP Link-Local Next Hop Capability
draft-kumar-idr-link-local-nexthop-02.txt
Abstract
This document proposes a new BGP capability to allow route resolution
over IPv6 link-local next hop. It eliminates the requirement of
assigning a global IPv6 address for the next hop.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Link-Local Next Hop Capability . . . . . . . . . . . . . . . 3
3. Constructing the Next Hop field . . . . . . . . . . . . . . . 4
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Deployment Considerations . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informational References . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
BGP [RFC4271] implementations support peering over link-local IPv6
addresses [RFC4291]. However, for the prefixes advertised over such
a peering the resulting next hop attribute and route installation is
still dependent on the Next Hop carrying a global IPv6 address. For
the deployments where next hops need not have a scope beyond the
peering link, the configuration can be simplified by lifting the
requirement that the Next Hop field carry a global IPv6 address.
While the current proposal has no dependency on the link-local
peering (e.g. link-local next hops could be used over ipv4 peering
too), the use case with link-local peering offers clear advantages.
Link-local peering already mandates an interface to be attached
explicitly with the neighbor configuration. With the negotiation of
the proposed capability, a BGP speaker sends link-local addresses as
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the only IPv6 next hop address. Correspondingly, the receiving peer
resolves the routes in the context of the peering interface.
Many large modern data-center networks that are based on topologies
such as CLOS tend to be rather symmetric, and the BGP deployment in
such networks do not require next hops to have relevance across
peerings. Such BGP deployment models require BGP to run on each
link, and any ease or simplification of BGP configuration can result
in simplifying orchestration and configuration management. This
proposal is a step in that direction.
With the requirement of any global interface address being removed by
this new capability, BGP neighbor configuration can be further
simplified by making it (look) address-family independent. E.g BGP
can just take interface name for the peer config and link-local IPv6
address of the peer can be learned via a discovery protocol running
on the link or by an out-of-band tool. In essence, link-local next
hop in combination with [RFC5549] makes it possible to achieve an
unnumbered interface-like solution [RFC5309] in BGP.
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. Link-Local Next Hop Capability
The LINK-LOCAL-ONLY-NEXT-HOP capability is a new BGP capability. A
BGP speaker that supports capabilities advertisement [RFC5492] in an
OPEN message should send this capability only when:
1. It is capable of sending link-local IPv6 address as the only next
hop address for a route.
2. The implementation is capable of processing link-local address
next hops with the help of peer interface binding to come up with
interface specific next hops for its routing table.
The presence of this capability does not affect the support of global
IPv6 only (16 bytes next hop) and global IPv6 combined with link-
local IPv6 (32 bytes next hop), which should continue to be supported
as before.
The Capability Code for this capability is specified in the IANA
Considerations section of this document. The Capability Length field
of this capability is 0.
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3. Constructing the Next Hop field
Section 3 of [RFC2545] standardizes IPv6 next-hop construction. Here
we suggest modifications required for link-local next hop
construction.
A BGP speaker shall advertise to its peer in the Network Address of
Next Hop field the link-local IPv6 address of the next hop.
The value of the Length of Next Hop Network Address field on a
MP_REACH_NLRI attribute shall be set to 16.
For iBGP peers configured as a route-reflector, when route-reflector
isn't configured to be in the data-path, the proposed link-local
(only) next hops MUST not be reflected.
In general, implementations should not relay the link-local only next
hop. Implementations supporting this capability should provide a way
to handle the relay of link-local only next hops over point-to-point
links (route-reflector and EBGP-to-IBGP cases) by either:
o an implicit next-hop-self.
o providing a configuration to enable next-hop-self. In this case,
the link-local next hop MUST not be relayed, if this knob is not
enabled.
Note: On a route-reflector, when source of link-local only next hop
and route-reflector client are on the same broadcast segment, then
implicit next-hop-self should not be done. Same goes for eBGP to
iBGP scenarios.
4. Operation
A BGP speaker that is willing to use (send and receive) only link-
local addresses as next hops with a peer SHOULD advertise the LINK-
LOCAL-ONLY-NEXT-HOP Capability to the peer using BGP Capabilities
advertisement.
[draft-kato] recommended implementations to ignore the ipv6 global
next hop if it didn't match any of the link's global addresses. The
proposal has the following limitations:
o It results in poor error handling, specifically for next hop
validation.
o It does not allow the sender to set a global next hop value that
is _not_ one of the assigned prefixes on the link.
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o It does not specify the behavior for IBGP sessions.
o A global next hop field has to be always present in the UPDATE
messages.
We formalize this idea with the proposed new capability, so that the
peers have the flexibility to include both link-local and global next
hops or link-local only next hop. The error handling of messages is
not compromised.
5. Deployment Considerations
The usage of this capability is restricted to the cases where the
scope of the next hop is limited to the peering interface. This
restriction comes from the fact that link-local IPv6 addresses are
link-scoped, therefore link-local address of the one peer can not be
used as next hop if its to be carried with the updates over another
peer.
6. Acknowledgments
We would like to thank Daniel Walton for his comments and
suggestions.
7. IANA Considerations
This document defines a new link-local next hop capability. IANA is
requested to assign a capability number to the same.
8. Security Considerations
There are no additional security risks introduced by this design.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing", RFC 2545, March
1999.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
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[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC5309] Shen, N. and A. Zinin, "Point-to-Point Operation over LAN
in Link State Routing Protocols", RFC 5309, October 2008.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, February 2009.
[RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network
Layer Reachability Information with an IPv6 Next Hop", RFC
5549, May 2009.
9.2. Informational References
[draft-kato]
"http://tools.ietf.org/html/
draft-kato-bgp-ipv6-link-local-00", September 2001.
Authors' Addresses
Vipin Kumar
Cumulus Networks
185 E. Dana Street
Mountain View, CA 94041
USA
Email: vipin@cumulusnetworks.com
Pradosh Mohapatra
Sproute Networks
Email: mpradosh@yahoo.com
Dinesh Dutt
Cumulus Networks
185 E. Dana Street
Mountain View, CA 94041
USA
Email: ddutt@cumulusnetworks.com
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Mike Valentine
Goldman Sachs
30 Hudson St
Jersey City, NY 07302
USA
Email: michael.j.valentine@gs.com
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