Network Working Group Chris Metz
Internet Draft Luca Martini
Expires: May 2006 Cisco Systems
Florin Balus
Jeff Sugimoto
Nortel Networks
October 20, 2005
AII Types for Aggregation
draft-metz-aii-aggregate-01.txt
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Copyright Notice
Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract
[PWE3 Control] defines the signaling mechanisms for establishing
point-to-point pseudowires between two provider edge (PE) nodes. The
Generalized ID FEC element contained in PWE3 signaling protocols
include TLV fields that identify pseudowire endpoints called
attachment individual identifiers (AII). This document defines an AII
structure in the form of new AII type-length-value fields that
supports AII aggregation for improved scalability. 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 New AII Types....................................4
2.1. PWid AII Type.............................................4
2.2. Short Prefix AII Type.....................................5
2.3. Long Prefix AII Type......................................7
3. IANA Considerations............................................9
4. Security Considerations........................................9
5. Acknowledgments...............................................10
Author's Addresses...............................................11
Intellectual Property Statement..................................12
Disclaimer of Validity...........................................12
Copyright Statement..............................................13
Acknowledgment...................................................13
1. Introduction
[PWE3-CONTROL] 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
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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.
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 summarizes or aggregates a large number of individual AII values
could significantly reduce the burden on AII distribution mechanisms
(e.g. MP-BGP) and on PE memory needed to store this AII information.
An aggregate AII structure and corresponding IP next hop address
could form the basis for enabling inter-domain MS-PW routing and
signaling in a manner similar to the way that BGP-advertised IP
address prefixes and next hops enable inter-domain IP routing. This
would be useful in large inter-domain VPWS networks where PWs are
established between local and remote PE based on customer need [REQ-
MH-PW]. Note that this document does not discuss if, how, or where in
the network the aggregation of AII values is performed, how AII
aggregate reachability is distributed nor does it discuss how PW
setup messages are routed through a network based on AII reachability
information.
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 NATs during signaling. Globally unique AII
values could aid in troubleshooting and could be subjected to source-
validity checks during AII distribution and signaling.
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An AII automatically derived from a providers existing IP address
space can simplify the provisioning process. In addition an AII
structure that is backwards compatible with previous endpoint
identifier semantics (i.e. PWid) and other L2VPN provisioning models
[L2VPN-SIG] would help providers to converge upon a PW provisioning
and signaling behavior employing GID FEC TLVs.
In summary the purpose of this document is to define an AII structure
based on [PWE3-CONTROL] that:
o Enables many discrete attachment individual identifiers to be
aggregated into a single AII aggregate. This will enhance
scalability by reducing the burden on AII distribution mechanisms
and on PE memory.
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.
o Supports a uniform PW signaling mechanism employing the GID FEC
TLV structure for endpoints provisioned with the AII types defined
in this document, other L2VPN provisioning techniques and
including those previously configured with the older FEC 128 PWid
value.
This is accomplished by defining three new AII types and associated
formats of the value fields.
2. Structure for New AII Types
[PWE3-CONTROL] defines the format of the GID FEC TLV and the use and
semantics of the attachment group identifier (AGI).
New AII types and the format of their associated AII value fields are
defined next.
2.1. PWid AII Type
The PWid AAI type provides GID FEC 129 signaling compatibility with
those endpoint identifiers provisioned with the 32-bit PWid values.
Unlike the FEC 128 encoding, the values of the PWid AII type do not
have to match on the local and remote PE nodes.
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The PWid AII type can also be used when the provisioning model
warrants definition of a fixed-length 32-bit value used to identify
a particular attachment circuit [L2VPN-SIG]. The value of the PWid
AII type can be globally unique or combined with some other value
(e.g. AGI) to provide a globally unique identifier if warranted by
the provisioning model.
The PWid AII type is encoded as the following:
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=01 | Length | PWid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PWid (contd.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o AII Type = 0x01
o Length = Length of the value field in octets. The length is set to
4 for this AII type.
o PWid = Fixed-length 32-bit value.
The provisioning models employing this AII type require that the
entire 32-bit value field (fully-qualified) is processed by AII
distribution mechanisms. This means it CANNOT be aggregated.
2.2. Short Prefix AII Type
The Short Prefix AII type 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.
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The Short Prefix AII type uses a combination of a providers 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. It is termed the Short Prefix AII type because of the
shorter 32-bit prefix used here as compared to the longer 256-bit
prefix used in the Long Prefix AII type defined in the next section.
The encoding of the Short Prefix AII type is shown in figure 1.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Short Prefix AII TLV Structure
o AII Type = 0x02
o Length = length of value field in octets. The length is set to 10
if the AC ID is NULL and 14 if the AC ID is non-null.
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o Global ID = This is a 6 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 providers Autonomous System Number, a global
unicast IPv6 /48 prefix assigned to the provider or some other
globally unique value up to 6 octets in length. It is expected
that the global ID will be derived from the globally unique AS
number of the autonomous system hosting the PEs containing the
actual AIIs. 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 providers AS number as a global
ID DOES NOT have anything at all to do with the use of the AS
number in protocols such as BGP.
o Prefix = The 32-bit prefix is a value assigned by the provider or
it can be automatically derived from the PEs /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 providers
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 10. If the AC ID is present then
the length field is set to 14 octets.
2.3. Long Prefix AII Type
The Long Prefix AII type employs a global ID and 256-bit prefix field
(versus 32 bits for the Short Prefix AII type) to create AII values.
The Long Prefix AII type might be useful to providers with
provisioning systems or AII addressing schemes that exceed 32 bits in
length. It can also be used to auto-generate AII values based on /128
IPv6 and /32 IPv4 PE loopbacks.
The encoding of the Long Prefix AII type is shown in figure 2:
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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=03 | Length | Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global ID (contd.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| |
| Prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 Long Prefix AII TLV Structure
o AII Type = 0x03
o Length = length of value field in octets. The length is set to 38
for this AII type.
o Global ID = This is a 6 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 providers Autonomous System Number, a global
unicast IPv6 /48 prefix assigned to the provider or some other
globally unique value up to 6 octets in length. It is expected
that the global ID will be derived from the globally unique AS
number of the autonomous system hosting the PEs containing the
actual AIIs. 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 providers AS number as a global
ID DOES NOT have anything at all to do with the use of the AS
number used in protocols such as BGP.
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o Prefix = The 256-bit Prefix is a value assigned by the provider or
it can be automatically derived from the PEs local addressing
scheme such as IPv6 or IPv4.
This AII type does not employ an optional AC ID field. This is
because there are sufficient bits available in the prefix field to
hold a fully qualified target PE value auto-generated from even a
long address type such as IPv6 with the remainder available for local
attachment circuit identification.
3. IANA Considerations
This document requests that IANA allocate three AII types from the
"Attachment Individual Identifier (AII) Type" registry defined in
[IANA].
The suggested values for the AAI types are:
Value Description
0x01 PWid
0x02 Short Prefix
0x03 Long Prefix
4. Security Considerations
AII values appear in AII distribution protocols [MP-BGP-AUTO-DISC]
and PW signaling protocols [PWE3-CONTROL] 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.
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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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References
[PWE3-CONTROL], Pseudowire Setup and Maintenance using LDP,
draft-ietf-pwe3-control-protocol-17.txt, June 2005
[IANA], "IANA Allocations for pseudo Wire Edge to Edge Emulation
(PWE3)" Martini,Townsley, draft-ietf-pwe3-iana-allocation-
12.txt, work in progress), September 2005
[L2VPN-SIG], Provisioning Models and Endpoint Identifiers in L2VPN
Signaling, draft-ietf-l2vpn-signaling-06.txt, Sept. 2005
[REQ-MH-PW], Requirements for inter domain Pseudo-Wires, draft-
ietf-pwe3-ms-pw-requirements-00.txt, Internet Draft, June
2005
[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.
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Ottawa, Ontario, CANADA
Email: balus@nortel.com
Jeff Sugimoto
Nortel
3500 Carling Ave.
Ottawa, Ontario, CANADA
Email: sugimoto@nortel.com
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