Network working group X. Xu
Internet Draft Huawei
Category: Standard Track K. Lee
China Telecom
Expires: January 2013 July 16, 2012
BGP Tunnel Address Prefix Attribute and Tunnel Address Prefix
Extended Community
draft-xu-idr-tunnel-address-prefix-01
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Abstract
This document describes a new BGP attribute referred to as Tunnel
Address Prefix Attribute and a new BGP address specific extended
community referred to as Tunnel Address Prefix Extended Community,
both of which are intended for facilitating the load-balancing of
IP/GRE tunneled traffic (e.g., L3VPN-over-GRE traffic) in the core
of IP-enabled Packet Switch Networks (PSN).
Conventions used in this document
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].
Table of Contents
1. Introduction ................................................ 3
2. Terminology ................................................. 4
3. Tunnel Address Prefix Attribute ............................. 4
4. Tunnel Address Prefix Extended Community .................... 5
5. Functionality Description ................................... 6
5.1. Egress Routers ......................................... 6
5.2. Ingress Routers......................................... 6
5.3. Intermediate Routers ................................... 6
6. Applicability ............................................... 6
7. Security Considerations ..................................... 7
8. IANA Considerations ......................................... 7
9. Acknowledgements ............................................ 7
10. References ................................................. 7
10.1. Normative References .................................. 7
10.2. Informative References ................................ 7
Authors' Addresses ............................................. 8
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1. Introduction
Equal Cost Multi-Path (ECMP) and Link Aggregation Group (LAG) are
widely used in the core of IP-enabled Packet Switch Networks (PSN)
for load-balancing purposes. Most core routers in the IP-enabled PSN
are capable of load-balancing IP traffic flows across ECMP paths
and/or LAG based on the hash of the five-tuple of UDP/TCP packets
(i.e., source IP address, destination IP address, source port,
destination port, and protocol) or some fields in the IP header of
non-UDP/TCP packets (e.g., source IP address, destination IP
address). However, in the L3VPN [RFC4364], L2VPN and Softwire mesh
[RFC5565] scenarios, distinct customer traffic flows between a given
tunnel endpoint pair (e.g., the PE pair in the L3VPN context) would
be encapsulated with the same IP/GRE tunnel header prior to
traversing the core of IP PSN. In addition, since the IP/GRE
encapsulated traffic is neither TCP nor UDP, core routers therefore
could only perform hash calculation on the fields in the IP header
of IP/GRE tunnels. As a result, core routers could not achieve an
effective load-balancing for these IP/GRE tunneled traffic flows in
the core network due to the lack of adequate entropy information.
[RFC5640] describes a method for improving the load-balancing in
Softwire mesh networks [RFC5565]. However, this method requires core
routers to be able to perform hash calculation on the fields
including the specific "load-balancing" field contained in the
L2TPv3 or GRE tunnel header. [Entropy-Label] proposes to use the
"entropy labels" for achieving a better load-balancing for MPLS
traffic flows in the core of MPLS-enabled PSN. Although the entropy
label could be inserted in the "Key" field of the GRE header by
ingress PE routers in the case where the PSN is IP enabled rather
than MPLS enabled, it still requires core routers to be capable of
performing hash calculation on the "entropy label" contained in the
GRE tunnel header. Any of the above two load-balancing methods
requires a change to the date plane of core routers.
This document describes an alternative load-balancing method
suitable for the above scenarios, which is backwards compatible to
those already-deployed core routers that could only perform hash
calculation on the fields in the IP header in the case of IP/GRE
tunneled traffic flows. The basic idea of this method is: a given
(tunnel) egress router signals to (tunnel) ingress routers a special
prefix called "tunnel address prefix" via BGP and any addresses
beginning with that prefix would be used by those ingress routers as
tunnel destination addresses when tunneling traffic towards that
egress router. Therefore distinct traffic flows between that tunnel
endpoint pair could be encapsulated with as many different tunnel
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destination addresses as possible. In this way, core routers could
achieve a better load-balancing for those IP/GRE tunneled traffic
through performing hash calculation just on the fields in the IP
header.
2. Terminology
This memo makes use of the terms defined in [RFC4364] and [RFC5565].
3. Tunnel Address Prefix Attribute
For a given BGP router to tell remote BGP routers what tunnel
destination addresses could be used when tunneling traffic flows to
it, a new BGP attribute contained in the Encapsulation SAFI
[RFC5512], referred to as "Tunnel Address Prefix Attribute", could
be used to indicate the available tunnel destination addresses to be
used.
The Tunnel Address Prefix attribute is an optional transitive
attribute. The TLV is structured 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel Address Prefix Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Tunnel Address Prefix Type (2 octets): indicates the Value
field of such TLV contains the tunnel address prefix information
in the form of IP address and subnet mask pair.
- Length (2 octets): indicates the total number of octets of the
value field. If the AFI of the Encapsulation SAFI is IPv4, the
length value is set to 64; otherwise if the AFI is IPv6, the
length value is set to 256.
- Value (variable): contains the tunnel address prefix
information in the form of IP address and subnet mask pair.
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4. Tunnel Address Prefix Extended Community
Here, we also define an address specific extended community referred
to as Tunnel Address Prefix extended community that can be attached
to BGP UPDATE messages to indicate the available tunnel destination
addresses to be used when tunneling traffic flows from an ingress
router to an egress router. This extended community is useful in the
case where the Encapsulation SAFI capability is not supported
between BGP routers or one really wants to specify different tunnel
destination address prefixes for distinct sets of traffic flows. For
example, one wants to assign two different tunnel address prefixes
for traffic flows destined for prefix X and Y respectively.
IPv4 Tunnel Address Prefix extended community is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x01 | Sub-Type | Global Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Administrator (cont.) | Local Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value of the high-order octet of the extended type field is
0x01, which indicates it is transitive across ASes. The value of
the low-order octet of the extended type field is to be defined.
The Global Administrator sub-field contains an IPv4 unicast
address while the Local Administrator sub-field contains the
corresponding Prefix Length.
IPv6 Tunnel Address Prefix extended community is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x00 | Sub-Type | Global Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Administrator (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Administrator (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Administrator (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Administrator (cont.) | Local Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The value of the high-order octet of the extended type field is
0x00, which indicates it is transitive across ASes. The value of
the low-order octet of the extended type field is to be defined.
The Global Administrator sub-field contains an IPv6 unicast
address while the Local Administrator sub-field contains the
corresponding Prefix Length.
5. Functionality Description
5.1. Egress Routers
An egress router could attach the above BGP Tunnel Address Prefix
attribute or extended community to BGP UPDATE messages in order to
indicate the available tunnel destination addresses to be used by
any ingress routers when tunneling traffic flows to it. In addition,
it SHOULD create the corresponding loopback interface for each IP
address within that prefix and accordingly advertise a route for
that prefix via IGP. As such, it could receive and process those
IP/GRE tunneled traffic flows destined for any of those addresses
beginning with that prefix.
5.2. Ingress Routers
For an ingress router receiving the above BGP Tunnel Address Prefix
attribute or extended community announced by a given egress router,
it could use any addresses beginning with the tunnel address prefix,
in addition to the BGP next-hop address contained in the
MP_REACH_NLRI attribute, as tunnel destination addresses when
tunneling traffic flows towards that egress router.
5.3. Intermediate Routers
There is no special requirement on Intermediate Routers (i.e., core
routers). In other words, they could perform load-balancing of the
IP/GRE tunneled traffic on basis of the hash of the fields in the IP
headers as normal.
6. Applicability
The load-balancing approach described in this document is suitable
for many scenarios including but not limited to L3VPN [RFC4364], 6PE
[RFC4798], Softwire mesh [RFC5565], BGP free core and L2VPN
including VPLS [RFC4761, RFC4762] and E-VPN [E-VPN]. In the existing
VPLS case where BGP is used for auto-discovery, the above BGP Tunnel
Address Prefix attribute or extended community would be attached to
the BGP update messages as well. Once a customer MAC address is
learnt against a given BGP next-hop address, any addresses beginning
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with the Tunnel Address Prefix which is associated with that BGP
next-hop address could be used as tunnel destination addresses when
tunneling MAC frames destined for that MAC address.
7. Security Considerations
TBD.
8. IANA Considerations
The type code of the Tunnel Address Prefix Attribute needs to be
allocated by IANA. Meanwhile, a new Sub-Type of the Address Specific
BGP Extended Communities of IPv4 and IPv6 respectively SHOULD also
be assigned by IANA.
9. Acknowledgements
Thanks to Robert Raszuk for his valuable comments on this document.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
[RFC5640] Filsfils, C., Mohapatra, P and C. Pignataro, "Load-
Balancing for Mesh Softwires", RFC 5640, August 2009.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006.
[RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended
Communities Attribute", RFC5701, November 2009.
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the
BGP Tunnel Encapsulation Attribute", RFC 5512, April
2009.
[RFC5565] Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh
Framework", RFC 5565, June 2009.
[RFC4364] "BGP/MPLS IP VPNs", Rosen, Rekhter, et. al., February 2006
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[Entropy-Label] Kompella, K., Drake, J., Amante, S., Henderickx, W.,
and L. Yong, "The Use of Entropy Labels in MPLS
Forwarding", draft-ietf-mpls-entropy-label-01, work in
progress, October, 2011.
[RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling", RFC
4761, January 2007.
[RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service
(VPLS) Using Label Distribution Protocol (LDP) Signaling",
RFC 4762, January 2007.
[E-VPN] Aggarwal et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-00.txt, work in progress, February, 2012.
Authors' Addresses
Xiaohu Xu
Huawei Technologies,
Beijing, China
Phone: +86-10-60610041
Email: xuxiaohu@huawei.com
Kai Lee
China Telecom,
Beijing, China.
Email: Leekai@ctbri.com.cn