PWE3 Working Group Chris Metz
Internet Draft Luca Martini
Expires: April 2007 Cisco Systems
Florin Balus
Jeff Sugimoto
Nortel Networks
October 4, 2006
Pseudowire Attachment Identifiers for Aggregation and VPN
Autodiscovery
draft-ietf-pwe3-aii-aggregate-01.txt
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Copyright Notice
Copyright (C) The Internet Society (2006). All Rights Reserved.
Abstract
The signaling protocols used to establish point-to-point pseudowires
include type-length-value (TLV) fields that identify pseudowire
endpoints called attachment individual identifiers (AII). This
document defines AII structures in the form of new AII type-length-
value fields that support AII aggregation for improved scalability
and VPN autodiscovery. It is envisioned that this would be useful in
large inter-domain virtual private wire service networks where
pseudowires are established between selected local and remote PE
nodes based on customer need.
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 Error!
Reference source not found..
Table of Contents
1. Introduction...................................................2
2. Structure for the New AII Type.................................4
2.1. AII Type 1................................................4
2.2. AII Type 2................................................4
3. IANA Considerations............................................6
4. Security Considerations........................................6
5. Acknowledgments................................................6
Author's Addresses................................................7
Intellectual Property Statement...................................8
Disclaimer of Validity............................................8
Copyright Statement...............................................8
Acknowledgment....................................................9
1. Introduction
[RFC4447] defines the signaling mechanisms for establishing point-to-
point pseudowires (PWs) between two provider edge (PE) nodes. When a
PW is set up, the LDP signaling messages include a forwarding
equivalence class (FEC) element containing information about the PW
type and an endpoint identifier used in the selection of the PW
forwarder that binds the PW to the attachment circuit at each end.
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There are two types of FEC elements defined for this purpose: PWid
FEC (type 128) and the Generalized ID (GID) FEC (type 129). The PWid
FEC element includes a fixed-length 32 bit value called the PWid that
serves as an endpoint identifier. The same PWid value must be
configured on the local and remote PE prior to PW setup.
The GID FEC element includes TLV fields for attachment individual
identifiers (AII) that, in conjunction with an attachment group
identifier (AGI), serve as PW endpoint identifiers. The endpoint
identifier on the local PE (denoted as <AGI, source AII or SAII>) is
called the source attachment identifier (SAI) and the endpoint
identifier on the remote PE (denoted as <AGI, target AII or TAII>) is
called the target attachment identifier (TAI). The SAI and TAI can be
distinct values. This is useful for applications and provisioning
models where the local PE (with a particular SAI) does not know and
must somehow learn (e.g. via MP-BGP auto-discovery) of remote TAI
values prior to launching PW setup messages towards the remote PE.
The use of the GID FEC TLV provides the flexibility to structure
(source or target) AII values to best fit particular application or
provisioning model needs [L2VPN-SIG]. For example an AII structure
that enables many individual AII values to be identified as a single
value could significantly reduce the burden on AII distribution
mechanisms (e.g. MP-BGP) and on PE memory needed to store this AII
information. It should be noted that PWE3 signaling messages will
always include a fully qualified AII value.
An AII that is globally unique would facilitate PW management and
security in large inter-AS and inter-provider environments. Providers
would not have to worry about AII value overlap during provisioning
or the need for AII network address translation (NAT) boxes during
signaling. Globally unique AII values could aid in troubleshooting
and could be subjected to source-validity checks during AII
distribution and signaling. An AII automatically derived from a
provider’s existing IP address space can simplify the provisioning
process.
This document defines an AII structure based on [RFC4447] that:
o Enables many discrete attachment individual identifiers to be
summarized into a single AII summary value. This will enhance
scalability by reducing the burden on AII distribution mechanisms
and on PE memory.
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o Ensures global uniqueness if desired by the provider. This will
facilitate Internet-wide PW connectivity and provide a means for
providers to perform source validation on the AII distribution
(e.g. MP-BGP) and signaling (e.g. LDP) channels.
This is accomplished by defining new AII types and the associated
formats of the value field.
2. Structure for the New AII Type
[RFC4447] defines the format of the GID FEC TLV and the use and
semantics of the attachment group identifier (AGI).
2.1. AII Type 1
AII Type 1 has been allocated by IANA for use with provisioning
models requiring a fixed-length 32-bit value [L2VPN-SIG]. This value
is unique on the local PE.
2.2. AII Type 2
The AII Type 2 structure permits varying levels of AII summarization
to take place thus reducing the scaling burden on the aforementioned
AII distribution mechanisms and PE memory. In other words it no
longer becomes necessary to distribute or configure all individual
AII values (which could number in the tens of thousands or more) on
local PEs prior to establishing PWs to remote PEs. The details of how
and where the aggregation of AII values is performed and then
distributed as AII reachability information are not discussed in this
document.
AII Type 2 uses a combination of a provider’s globally unique
identifier (Global ID), a 32-bit prefix field and an optional 4-octet
attachment circuit identifier field to create globally unique AII
values.
The encoding of AII Type 2 is shown in figure 1.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type=02 | Length | Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global ID (contd.) | Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix (contd.) | AC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 AII Type 2 TLV Structure
o AII Type = 0x02
o Length = length of value field in octets. The length is set to 8
if the AC ID is NULL and 12 if the AC ID is non-null.
o Global ID = This is a 4 octet field containing a value that is
unique to the provider. The global ID can contain the 2 octet or 4
octet value of the provider’s Autonomous System Number (ASN). It
is expected that the global ID will be derived from the globally
unique ASN of the autonomous system hosting the PEs containing the
actual AIIs. The presence of a global ID based on the provider’s
ASN ensures that the AII will be globally unique.
If the PE hosting the AIIs is present in an autonomous system
where the provider is not running BGP, chooses not to expose this
information or does not wish to use the global ID, then the global
ID field MUST be set to zero. If the global ID is derived from a
2-octet AS number, then the high-order 4 octets of this 4 octet
field MUST be set to zero.
Please note that the use of the provider’s ASN as a global ID DOES
NOT have anything at all to do with the use of the ASN in
protocols such as BGP.
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o Prefix = The 32-bit prefix is a value assigned by the provider or
it can be automatically derived from the PE’s /32 IPv4 loopback
address. Note that it is not required that the 32-bit prefix have
any association with the IPv4 address space used in the provider’s
IGP or BGP for IP reachability.
o Attachment Circuit (AC) ID = This is a fixed length four octet
field used to further refine identification of an attachment
circuit on the PE. The inclusion of the AC ID is used to identify
individual attachment circuits that share a common prefix.
If the AC ID is not present then the AC ID field MUST be null and
the AII Length field is set to 8. If the AC ID is present then the
length field is set to 12 octets.
3. IANA Considerations
This document requests that IANA allocate a value from the
"Attachment Individual Identifier (AII) Type" registry defined in
[RFC4446].
The suggested value for this AII type is 0x02.
4. Security Considerations
AII values appear in AII distribution protocols [MP-BGP-AUTO-DISC]
and PW signaling protocols [RFC4447] and are subject to various
authentication schemes (i.e. MD5) if so desired.
The use of global ID values (e.g. ASN) in the inter-provider case
could enable a form of source-validation checking to ensure that the
AII value (aggregated or explicit) originated from a legitimate
source.
5. Acknowledgments
Thanks to Carlos Pignataro, Scott Brim, Skip Booth, George Swallow
and Bruce Davie for their input into this document.
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Normative References
[RFC4447], “Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)”, RFC4447, April 2006
[RFC4446], "IANA Allocations for Pseudowire Edge to Edge Emulation
(PWE3)", RFC4446, April 2006
[L2VPN-SIG], “Provisioning, Autodiscovery, and Signaling in L2VPNs”,
draft-ietf-l2vpn-signaling-08.txt, B. Davie, et al., May
2006
[MP-BGP-AUTO-DISC], “Using BGP as an Auto-Discovery Mechanism for
Layer-3 and Layer-2 VPNs”, Ould-Brahim, H. et al, draft-
ietf-l3vpn-bgpvpn-auto-06.txt, June 2005
Author's Addresses
Chris Metz
Cisco Systems, Inc.
3700 Cisco Way
San Jose, Ca. 95134
Email: chmetz@cisco.com
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
Email: lmartini@cisco.com
Florin Balus
Nortel
3500 Carling Ave.
Ottawa, Ontario, CANADA
Email: balus@nortel.com
Jeff Sugimoto
Nortel
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3500 Carling Ave.
Ottawa, Ontario, CANADA
Email: sugimoto@nortel.com
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