Internet Engineering Task Force H. Chen
Internet-Draft Huawei Technologies
Intended status: Standards Track N. So
Expires: January 12, 2012 Verizon Inc.
July 11, 2011
Extensions to RSVP-TE for P2MP LSP Ingress Local Protection
draft-chen-mpls-p2mp-ingress-protection-03.txt
Abstract
This document describes extensions to Resource Reservation Protocol -
Traffic Engineering (RSVP-TE) for locally protecting the ingress node
of a Traffic Engineered (TE) Point-to-MultiPoint (P2MP) Label
Switched Path (LSP) in a Multi-Protocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) network.
Status of this Memo
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Conventions Used in This Document . . . . . . . . . . . . . . 4
4. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. An Example of Ingress Local Protection . . . . . . . . . . 4
4.2. Set up of Backup P2MP sub Tree . . . . . . . . . . . . . . 5
4.3. Forwarding State for Backup P2MP sub Tree . . . . . . . . 5
4.4. Detection of Failure around Ingress . . . . . . . . . . . 6
5. LSP Information Message . . . . . . . . . . . . . . . . . . . 6
5.1. Format of LSP Information Message . . . . . . . . . . . . 7
5.2. Processing of LSP Information Message . . . . . . . . . . 7
6. LSP Information Confirmation Message . . . . . . . . . . . . . 8
6.1. Format of LSP Information Confirmation Message . . . . . . 8
6.2. Processing of LSP Information Confirmation Message . . . . 8
7. PATH Messages for Backup P2MP sub Tree . . . . . . . . . . . . 9
7.1. Construction of PATH Messages . . . . . . . . . . . . . . 9
7.2. Processing of PATH Messages . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
RFC4090 "Fast Reroute Extensions to RSVP-TE for LSP Tunnels"
describes two methods to protect P2P LSP tunnels or paths at local
repair points. For a P2P LSP, the local repair points may comprise a
number of intermediate nodes between the ingress node and the egress
node of the P2P LSP. The first method is a one-to-one backup method,
where a detour backup P2P LSP for each protected P2P LSP is created
at each potential point of local repair. The second method is a
facility bypass backup protection method, where a bypass backup P2P
LSP tunnel is created using MPLS label stacking to protect a
potential failure point for a set of P2P LSP tunnels. The bypass
backup tunnel can protect a set of P2P LSPs that have similar backup
constraints.
RFC4875 "Extensions to RSVP-TE for P2MP TE LSPs" describes how to use
the one-to-one backup method and facility bypass backup method to
protect a link or intermediate node failure on the path of a P2MP
LSP. However, there is no mention of locally protecting an ingress
node failure in a protected P2MP LSP.
There exist two methods for protecting an ingress node of a P2MP LSP.
The first method deploys a backup P2MP LSP from a backup ingress node
to the destination nodes to protect the ingress node. The main
disadvantage of this method is that the backup P2MP LSP consumes
additional network bandwidth along the entire LSP paths. The impact
on network efficiency can be significant in case of large P2MP
deployments. In addition, the backup LSP often has to be manually
constructed so that the backup P2MP LSP does not route through the
unprotected ingress node, and it has to be linked to the primary LSP
logically at the head-end to allow the fast switching in case of
ingress failure.
The second method extends the existing ways of protecting an
intermediate node of a P2P LSP to protect an ingress node of a P2MP
LSP. The disadvantages of this method include extra work for
refreshing PATH messages and processing RESV messages for the P2MP
LSP in the backup ingress node.
This document defines extensions to RSVP-TE for locally protecting an
ingress node of a Traffic Engineered (TE) point-to-multipoint (P2MP)
Label Switched Path (LSP) through using a backup P2MP sub tree. The
new method overcomes the disadvantages described above. It can also
be applied for protecting an ingress node of a TE point-to-point
(P2P) LSP since a TE P2P LSP can be considered as a special case of a
TE P2MP LSP.
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2. Terminology
This document uses terminologies defined in RFC2205, RFC3031,
RFC3209, RFC3473, RFC4090, RFC4461, and RFC4875.
3. 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.
4. Mechanism
This section briefly describes a solution that locally protects an
ingress node of a P2MP LSP through using a backup P2MP sub tree. We
start with a simple example, and then present different parts of the
solution, which includes the creation of the backup P2MP sub tree,
the forwarding state for the backup P2MP sub tree, and the detection
of a failure in the ingress node.
4.1. An Example of Ingress Local Protection
Figure 1 below illustrates an example of using a backup P2MP sub tree
to locally protect the ingress of a P2MP LSP. The P2MP LSP to be
protected is from ingress node R1 to three egress/leaf nodes: L1, L2
and L3. The backup P2MP sub tree used to protect the ingress node R1
is from backup ingress node Ra to the next hop nodes R2 and R4 of the
ingress node R1 along the P2MP LSP. The traffic from source S may be
delivered to both R1 and Ra. R1 introduces the traffic into the P2MP
LSP, which is sent to the egress/leaf nodes L1, L2 and L3 along the
P2MP LSP. Ra normally does not put the traffic into the backup P2MP
sub tree, which is from Ra to R2 and R4. There may be a BFD session
between ingress node R1 and backup ingress node Ra. Ra uses this BFD
session to detect the failure of ingress R1. When Ra detects the
failure of R1, it imports the traffic from the source S into the
backup P2MP sub tree. The traffic from the sub tree is merged into
the P2MP LSP at R2 and R4, and then sent to the egress/leaf nodes L1,
L2 and L3 along the P2MP LSP.
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[R2]======[R3]=====[L1]
// |
// |
// |
// |
// /
// /
// /
+---[R1]======[R4]====[R5]=====[L2]
| ! / / \\
| ! / / \\
[S]--| ! / / \\
| ! / / \\
| !/ / \\
+---[Ra]---[Rb] \\
\\
\\
[L3]
Figure 1: P2MP sub Tree for Locally Protecting Ingress
After the failure of the ingress node R1, the refresh of the PATH
messages for the ingress node is not needed. Each of the next-hop
nodes of the ingress node will receive the PATH messages and the
refresh of the PATH messages for the backup P2MP sub tree from the
backup ingress node Ra, which make the P2MP LSP alive.
4.2. Set up of Backup P2MP sub Tree
For the ingress node of the P2MP LSP, a backup ingress node is
designated to protect it. The backup ingress node initiates the
creation of the backup P2MP sub tree from itself to the next-hop
nodes of the unprotected ingress node. The ingress node then sends
the P2MP LSP information to the backup ingress node.
The backup ingress node sets up the backup P2MP sub tree in a way
similar to setting up a P2MP tree or LSP from the signaling's point
of view. It constructs and sends RSVP-TE PATH messages along the
path for the backup P2MP sub tree with the final destinations (i.e,
egress/leaf nodes) matching the P2MP LSP. It receives and processes
RSVP-TE RESV messages that response to the PATH messages.
4.3. Forwarding State for Backup P2MP sub Tree
The forwarding state for the backup P2MP sub tree is different from
that for a P2MP LSP. After receiving the RSVP-TE RESV messages for
the backup P2MP sub tree, the backup ingress node creates a
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forwarding entry with an inactive state or flag. This forwarding
entry with an inactive state or flag is called an inactive forwarding
entry. In a normal operation, this inactive forwarding entry is not
used to forward any data traffic to be transported by the P2MP LSP,
even though the data traffic may be delivered to the backup ingress
node from an external node such as source node S in the above example
or network. The forwarding entry for the P2MP LSP is with an active
state or flag. Thus when the data traffic from the external node or
network reaches the ingress node of the P2MP LSP, it is imported into
the P2MP LSP tunnel through the active forwarding entry on the
ingress node.
When the ingress node fails, the inactive forwarding entry on the
backup ingress node is changed to active. Thus when the data traffic
from the external node reaches the backup ingress node, it is
imported into the backup P2MP sub tree. When the traffic arrives at
the next-hop nodes through the backup P2MP sub tree, it is merged
into the P2MP LSP to be transported to the destinations.
4.4. Detection of Failure around Ingress
There can be two different failure scenarios involving the ingress
node of a P2MP LSP that need to be detected.
o The failure of the ingress node (e.g. R1 of figure 1).
o The failure of the link between the source node and the ingress
node (e.g. the link between node S and node R1 in figure 1).
A failure of the ingress node can be detected through a BFD session
between the ingress node and the backup ingress node. A failure of
the link between the source node and the ingress node can be detected
by a BFD session running on the link.
After the backup ingress node detects any failure involving the
ingress node, it imports the traffic from the source node into the
backup P2MP sub tree. The traffic from the backup ingress node via
the sub tree is merged into the P2MP LSP on the next-hop nodes of the
ingress of the P2MP LSP, and then transported to the egress/leaf
nodes of the P2MP LSP.
5. LSP Information Message
LSP information messages are used to transfer the information about a
P2MP LSP to a backup ingress node from an ingress node. This section
describes the format of an LSP information message and processing of
the message.
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5.1. Format of LSP Information Message
The format of a P2MP LSP information message is illustrated below.
<LSP Information Message> ::=
<Common Header> [ <INTEGRITY> ]
[ [<MESSAGE_ID_ACK> | <MESSAGE_ID_NACK>] ...]
[ <MESSAGE_ID> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <EXPLICIT_ROUTE> ]
<LABEL_REQUEST>
[ <PROTECTION> ]
[ <LABEL_SET> ... ]
[ <SESSION_ATTRIBUTE> ]
[ <NOTIFY_REQUEST> ]
[ <ADMIN_STATUS> ]
[ <POLICY_DATA> ... ]
<sender descriptor>
[<S2L sub-LSP descriptor list>]
<RECORD_ROUTE>
<S2L sub LSP flow descriptor list>
The formats and values of the objects in a P2MP LSP information
message are similar to or the same as those of the corresponding
objects defined in RFC4875.
The value of the Msg Type field in the common header in the P2MP LSP
information message will be a new number such as 68 for the LSP
information message, or may be another number assigned by Internet
Assigned Numbers Authority (IANA).
5.2. Processing of LSP Information Message
Similar to sending an existing RSVP-TE message such as a PATH
message, the ingress node MUST send updated RSVP-TE LSP information
message to the backup ingress node whenever there is a change in the
RSVP-TE LSP information message. The ingress node MAY send the same
RSVP-TE LSP information message to the backup ingress node every
refresh interval if there is no change.
When the backup ingress node receives the RSVP-TE LSP information
message from the ingress node, the backup ingress node stores the LSP
information, constructs PATH messages, and sends the PATH messages
downstream accordingly. If the backup ingress node has not received
any RSVP-TE LSP information message for an extended period of time
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(e.g. a cleanup timeout interval), the backup ingress node SHALL
remove the information about the P2MP LSP, constructs PathTear
messages, and send the PathTear messages downstream accordingly.
6. LSP Information Confirmation Message
LSP information confirmation messages are used to confirm that the
corresponding LSP information messages are received. With the
confirmation messages, the refresh of the LSP information messages is
not needed. This section describes the format of an LSP information
confirmation message and processing of the message.
6.1. Format of LSP Information Confirmation Message
The format of a P2MP LSP information confirmation message is
illustrated below.
<LSP Information Confirmation Message> ::=
<Common Header> [ <INTEGRITY> ]
[ [<MESSAGE_ID_ACK> | <MESSAGE_ID_NACK>] ...]
[ <MESSAGE_ID> ]
<SESSION> <RSVP_HOP>
<sender descriptor>
The formats and values of the objects in a P2MP LSP information
confirmation message are similar to or the same as those of the
corresponding objects defined in RFC4875.
The value of the Msg Type field in the common header in the P2MP LSP
information confirmation message will be a new number such as 69 for
the LSP information confirmation message, or may be another number
assigned by Internet Assigned Numbers Authority (IANA).
6.2. Processing of LSP Information Confirmation Message
When the backup ingress node receives a RSVP-TE LSP information
message from the ingress node, it SHALL construct and send an LSP
confirmation message to the ingress node to acknowledge the message
received.
After the ingress node receives the LSP confirmation message, it
SHOULD stop refreshing the LSP information message.
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7. PATH Messages for Backup P2MP sub Tree
PATH messages for a backup P2MP sub tree has the same format as PATH
messages for a P2MP LSP defined in RFC 4875. This section describes
the construction of the PATH messages for the backup P2MP sub tree,
which is followed by processing of the PATH messages.
7.1. Construction of PATH Messages
When the backup ingress node receives an LSP information message, it
checks to see if anything has changed. If the message is a new
message or the information in the message has changed, then the PATH
messages for the backup P2MP sub tree are to be constructed as
follows.
First, a path to the next-hop nodes of the ingress node HAS to be
computed. The path MUST satisfy the constraints for the P2MP LSP and
not go through the ingress node.
If a path is computed successfully, then the PATH messages for the
backup P2MP sub tree are constructed based on the computed path and
the information message received, and sent downstream accordingly.
After sending the PATH messages, the backup ingress node receives
RESV messages from downstream nodes responding to the PATH messages.
It then processes the RESV messages and creates forwarding state
based on the information in the RESV messages.
If a path can not be found, the backup ingress node SHALL tear down
the backup P2MP sub tree created based the previous information
message.
The construction of a PATH message on a backup ingress node for a
backup P2MP sub tree is similar to the construction of a normal PATH
message on an ingress node for a P2MP LSP. It is based on LSP
information messages and a computed path for the backup P2MP sub
tree.
The EXPLICIT_ROUTE object and the objects in the S2L sub-LSP
descriptor list for the PATH message may be constructed through
combining the path computed to the next-hop nodes of the ingress node
and the path from the next-hop nodes to the destination nodes of the
P2MP LSP obtained from the RECORD_ROUTE object and the objects for
the S2L sub-LSP flow descriptor list in the LSP information messages.
7.2. Processing of PATH Messages
The processing of PATH messages on the intermediate nodes and the
destination nodes along the backup P2MP sub tree is the same as the
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processing of PATH messages for a P2MP LSP.
8. IANA Considerations
TBD
9. Acknowledgement
The author would like to thank Richard Li and Quintin Zhao for their
valuable comments on this draft.
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.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
[RFC4461] Yasukawa, S., "Signaling Requirements for Point-to-
Multipoint Traffic-Engineered MPLS Label Switched Paths
(LSPs)", RFC 4461, April 2006.
[RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
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"Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
10.2. Informative References
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, September 1999.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
Authors' Addresses
Huaimo Chen
Huawei Technologies
Boston, MA
USA
Email: Huaimochen@huawei.com
Ning So
Verizon Inc.
2400 North Glenville Drive
Richardson, TX 75082
USA
Email: Ning.So@verizonbusiness.com
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