Internet-Draft Juha Heinanen (Tutpro)
Expires: July 2004 W. Mark Townsley (Cisco)
Stephen Bailey (Sandburst)
Radius/L2TP Based VPLS
draft-ietf-l2vpn-l2tp-radius-vpls-00.txt
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This memo describes a simple mechanism to implement provider
provisioned Virtual Private LAN Service (VPLS) using Radius for PE
discovery and L2TP as the control and data plane protocol.
Table Of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 2
2. Service Description . . . . . . . . . . . . . . . . . . . 2
3. Adding a Site to a VPN . . . . . . . . . . . . . . . . . . 3
3.1. Configuration Actions . . . . . . . . . . . . . . . . . . 3
4. Connecting a Site to a VPN . . . . . . . . . . . . . . . . 3
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4.1. Configuration Actions . . . . . . . . . . . . . . . . . . 3
4.2. Protocol Actions . . . . . . . . . . . . . . . . . . . . . 3
5. Disconnecting a Site from a VPN . . . . . . . . . . . . . 5
5.1. Configuration Actions . . . . . . . . . . . . . . . . . . 5
5.2. Protocol Actions . . . . . . . . . . . . . . . . . . . . . 5
6. Removing a Site from a VPN . . . . . . . . . . . . . . . . 6
6.1. Configuration Actions . . . . . . . . . . . . . . . . . . 6
7. Failure Recovery . . . . . . . . . . . . . . . . . . . . . 6
8. Exponential Back-off Behavior . . . . . . . . . . . . . . 7
9. Data Plane . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 8
Full Copyright Statement . . . . . . . . . . . . . . . . . 9
1. Introduction
This memo describes a simple mechanism to implement provider
provisioned Virtual Private LAN Service (VPLS) [1] using Radius [5]
as the PE discovery protocol and L2TPv3 [3] as the control and data
plane protocol. Radius is deployed as described in [2], whereas
L2TP is deployed as described in [4] with minor changes.
An advantage of a directory (such as Radius) based discovery
solution for provider based VPNs is that it doesn't require BGP
implementation or configuration complexity in the PE routers and
can be easily deployed also in inter-AS cases where the VPN sites
are attached to PEs in more than one AS. An advantage of Radius as
a directory protocol is that it has been in Internet-wide use for
years and can thus be deployed without a new directory
infrastructure.
A similar directory based VPLS solution could be specified that
uses LDP for signaling and MPLS label stack encapsulation for data
transport. An L2TP based solution may, however, be preferable to
providers who are already familiar with L2TP and are not deploying
MPLS. An L2TP based solution may also be considered simpler to
manage, because L2TP tunnels are bidirectional and because L2TP
bundles control, data, and management planes in a single protocol.
2. Service Description
This memo supports VPLS service in a mode where each VPLS instance
(also called VPN for short) connects one or more CEs (also called
VPN sites) to a common virtual LAN. A VPN site can use either
802.1q tagged or untagged (but not both) Ethernet frames to
communicate with the other sites of the VPN. In case of tagged
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frames, each VPN site MUST use a single VLAN ID for the same VPN,
but the VLAN ID MAY differ at each VPN site.
VPLS service MAY support Differentiated Services treatment of
tagged or untagged Ethernet frames. In case of tagged frames, the
desired treatment of the frame is coded in the 802.1p User Priority
field. In case of untagged frames, all frames sent by a site
receive a default treatment. Differentiated Services treatment as
well as mapping of 802.1p User Priority values to DiffServ code
points of L2TP tunnels is VPLS specific and outside the scope of
this memo.
3. Adding a Site to a VPN
3.1. Configuration Actions
A site (a CE) is added to a VPN (a VPLS instance) by adding its
"user name", password, and VPN identifier record, for example:
<SiteX@vpnY.domainZ.net, secret, vpnY.domainZ.net>
to Radius database as described in [2]. After this configuration
action the site can be connected to the VPN at a PE.
4. Connecting a Site to a VPN
4.1. Configuration Actions
No configuration actions are needed if a site connects to the VPN
at a PE using a dynamic authentication protocol, such as
801.1x/EAP. Otherwise, the Ethernet interface of the PE to which
the site is going to be connected to MUST be configured with the
"user name" and password of the site, for example:
<providerP/SiteX@vpnY.domainZ.net, secret>
The provider prefix is only needed in case the site is connected to
a PE of a provider that is not the administrative owner of the VPN
(providerP in the above example).
The interface to which the site is connected to MAY be 802.1Q
tagged or untagged. In the former case, the VLAN ID that is used
to connect the site to the VPN MUST be specified.
4.2. Protocol Actions
The following protocol actions take place at the PE when a new VPN
site tries to authenticate itself with the PE or when the provider
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has configured a new VPN site to the PE:
(1) The PE issues Radius Access-Request for the CE as described in
[2]. If access is granted, the PE learns the identifier of
the CE's VPN and IP addresses of the VPN's PEs.
(2) If the PE already has site(s) that belong to the same VPN as
the new site, no other protocol actions take place at the PE.
(3) Otherwise the PE establishes an L2TP Control Connection with
each of the other PEs of the VPN unless one already exists.
The Pseudo Wire Capabilities List AVP of the Control
Connection MUST contain this and only this value:
0xTBD - Sessions without control word for connecting
Ethernet VLANs are allowed
(4) The PE establishes for this VPN an L2TP session with each of
the remote PEs unless one already exists. L2TP sessions are
established as defined in section 2.2 of [4] with the
following changes and clarifications:
L2TP sessions are established as for Incoming Calls using
ICRQ/ICRP/ICCN message exchange (see section 3.4.1 of [3]).
The Pseudo Wire Type AVP MUST have in its Attribute Value
field value:
0xTBD - Ethernet VLAN
The Application ID AVP MUST have in its Application Code field
value:
0xTBD - Radius/L2TP based VPLS
The End Identifier AVP MUST have in its Attribute Value field
the domain name of the VPN:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VPN Identifier (e.g. vpnY.domainZ.net) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following protocol actions take place in sequence at a PE when
it receives an L2TP Incoming-Call-Request from another PE for the
application described in this document:
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(1) The PE checks that itself and the other PE belong to the VPN
indicated by the End Identifier AVP. If the other PE is not
included in the PE's current list of other PEs of the VPN, the
PE issues an Access-Request request for an up to date list.
If the check fails, the PE responds with a Call-Disconnect-
Notify and no other protocol actions take place at the PE.
The Call-Disconnect-Notify MUST include a Result Code AVP with
Error Code and Error Message fields. The Result Code MUST
have the value 0x0002 (Session disconnected for the reason
indicated in Error Code) and the <Error Code, Error Message>
MUST have one of the two values:
<0xTBD, "Requesting PE does not belong to the VPN">
<0xTBD, "Requested PE does not belong to the VPN">
(2) The PE checks if it already has an L2TP session with the
calling PE for the VPN indicated by the End Identifier AVP.
If so, the PE responds with a Call-Disconnect-Notify and no
other protocol actions take place at the PE.
The Call-Disconnect-Notify MUST include a Result Code AVP with
Error Code and Error Message fields. The Result Code MUST have
the value 0x0002 (Session disconnected for the reason
indicated in Error Code) and the <Error Code, Error Message>
MUST have the value:
<0xTBD, "Session already exists for the VPN">
(3) Otherwise the PE accepts the request with an Incoming-Call-
Reply.
5. Disconnecting a Site from a VPN
5.1. Configuration Actions
When a site (CE) is to be disconnected from a VPN at a PE the "user
name" and password of the site is unconfigured from the Ethernet
interface to which it has been connected to.
5.2. Protocol Actions
The following protocol actions take place in sequence at the PE of
the disconnected site:
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(1) The PE issues a Stop Accounting-Request as described in 5.3 of
[2].
(2) If the disconnected site was the last site of the VPN at the
PE, the PE tears down any existing L2TP sessions for the VPN
by sending each remote PE a Call-Disconnect-Notify.
The Call-Disconnect-Notify MUST include a Result Code AVP with
Error Code and Error Message fields. The Result Code MUST
have the value 0x0002 (Session disconnected for the reason
indicated in Error Code) and the <Error Code, Error Message>
MUST have the value:
<0xTBD, "Requesting PE does not anymore belong to the VPN">
When a PE receives a Call-Disconnect-Notify from another PE for the
application described in this memo, no other protocol actions than
normal clean up of the corresponding L2TP session are needed at the
PE.
If the L2TP session that was torn down between two PEs was the last
session associated with the Control Connection, either PE MAY tear
down the Control Connection.
6. Removing a Site from a VPN
6.1. Configuration Actions
A site (a CE) is removed from a VPN (a VPLS instance) by removing
its
<CE user name, password, VPN identifier>
record from Radius database. This configuration action MUST
succeed only if Radius does not have a
<VPN identifier, PE IP address, CE user name>
record in its database where CE user name belongs to the removed
CE. This is true if the site has been first disconnected from the
VPN as described in section 5.
7. Failure Recovery
If a PE loses its Control Connection with another PE having site(s)
in a common VPN, the PE tries to re-establish the Control
Connection until (a) the Control Connection gets re-established or
(b) this PE or the other PE no longer have site(s) in this VPN.
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Once the Control Connection gets re-established, the PE re-
establishes an L2TP session with the other PE for this VPN as
described in section 4.2.
If an L2TP session gets teared down between two PEs and they still
have site(s) in the VPN of the teared down session, the two PEs try
to re-establish the session as described in section 4.2 as long as
the two PEs have site(s) in the VPN of the teared down session.
When a PE recovers from a crash, it adds each of the configured VPN
site(s) to their respective VPN(s) as described in section 4.2.
8. Exponential Back-off Behavior
If any protocol action does not succeed immediately, normal
behavior is that the PE keeps on trying with exponential back-off
until the action either succeeds or becomes invalid due to a change
in VPN configuration. If the protocol action fails for an
implementation specific prolonged period of time, the PE SHOULD
notify the "owner" of the VPN about the problem via a management
action.
9. Data Plane
The PEs that host the sites of a VPN act as virtual, fully
connected learning bridges for the VPN.
When a PE receives a Ethernet frame from a CE for a particular VPN,
it adds to it a 802.1q tag (if not already present) and sets the
VLAN ID to zero. Treatment of the 802.1p User Priority field is
VPLS specific and outside the scope of this memo.
When a PE needs to send an Ethernet frame to a VPN site connected
to it, it either overwrites the VLAN ID with the VLAN ID used by
the site for this VPN or removes the 802.1q tag if the interface of
the VPN site is untagged. Treatment of the 802.1p User Priority
field is VPLS specific and outside the scope of this memo.
When a PE needs to send an Ethernet frame to another PE, the PE
processes the frame as described in section 3 of [4] using the L2TP
session established for this VPLS instance. Mapping of the 802.1p
User priority value to DiffServ code point of the L2TP packet is
VPLS specific and outside the scope of this memo.
10. Security Considerations
Security of Radius/L2TP based VPNs depends on security of Radius
and L2TP. Security of Radius is covered in section 8 or [5] and
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security of L2TP is covered in section 8 of [3].
11. References
[1] Augustyn, et al., "Requirements for Virtual Private LAN
Services (VPLS)". draft-ietf-l2vpn-vpls-requirements-00.txt,
October 2002.
[2] Heinanen, "Using Radius for PE-Based VPN Discovery". draft-
heinanen-radius-pe-discovery-04.txt, June 2003.
[3] Lau, et al., "Layer Two Tunneling Protocol (Version 3)
"L2TPv3"". draft-ietf-l2tpext-l2tp-base-11.txt, October 2003.
[4] Aggarwal, et al., "Transport of Ethernet Frames over L2TPv3".
draft-ietf-l2tpext-pwe3-ethernet-01.txt, October 2002.
[5] Rigney, et al., "Remote Authentication Dial In User Service
(RADIUS)". RFC 2865, June 2000.
Authors' Addresses
Juha Heinanen
TutPro Inc.
Utsjoki, Finland
Email: jh@tutpro.com
W. Mark Townsley
Cisco Systems
7025 Kit Creek Road
PO Box 14987
Research Triangle Park, NC 27709
Email: mark@townsley.net
Stephen Bailey
Sandburst Corporation
600 Federal Street
Andover, MA 01810 USA
USA
Phone: +1 978 689 1614
Email: steph@sandburst.com
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