# US 7,586,841 B2 · System and method for protecting against failure of a TE-LSP tail-end node

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- Number: US 7,586,841 B2
- Document ID: US7586841B2
- Status: Granted
- Kind: B2
- Application number: 11/141,567
- Filed: 2005-05-31
- Published: 2006-11-30
- Granted: 2009-09-08
- Earliest claimed: 2005-05-31
- Assignees: Cisco Technology, Inc.
- Inventors: Jean-Philippe Vasseur
- Web page: https://patentgrep.com/patent/US7586841B2

## CPC

- H04L 41/12: Discovery or management of network topologies
- H04L 45/10: {Routing in connection-oriented networks, e.g. X.25 or ATM}
- H04L 45/12: Shortest path evaluation
- H04L 45/22: {Alternate routing}
- H04L 45/28: using route fault recovery
- H04L 45/50: using label swapping, e.g. multi-protocol label switch [MPLS]
- H04L 47/125: by balancing the load, e.g. traffic engineering
- H04L 47/70: Admission control; Resource allocation
- H04L 47/728: {for backup paths}
- H04L 47/746: {Reaction triggered by a failure}
- H04L 47/825: {Involving tunnels, e.g. MPLS}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A technique protects against failure of a tail-end node of a Traffic Engineering (TE) Label Switched Path (LSP) in a computer network. According to the protection technique, a node along the TE-LSP that is immediately upstream to the protected tail-end node and that is configured to protect the tail-end node (i.e., the “point of local repair” or PLR) learns reachable address prefixes (i.e., “protected prefixes”) of next-hop routers from the tail-end node (i.e., “next-next-hops,” NNHOPs to the protected prefixes from the PLR). The PLR creates a backup tunnel to each NNHOP that excludes the tail-end node, and associates each backup tunnel with one or more protected prefixes accordingly. When the tail-end node fails, Fast Reroute is triggered, and the protected prefix traffic (from the TE-LSP) is rerouted by the PLR onto an appropriate backup tunnel to a corresponding NNHOP. Notably, the PLR performs a penultimate hop popping (PHP) operation prior to forwarding the traffic along the backup tunnel(s).

## Claims

### Claim 1

A method for protecting against failure of a tail-end node of a Traffic Engineering (TE) Label Switched Path (LSP) in a computer network, the method comprising:
learning, at a point of local repair (PLR) along the TE-LSP, reachable address prefixes of next-hop routers from the tail-end node (NNHOPs);
creating a backup tunnel from the PLR to each NNHOP that excludes the tail-end node;
associating each backup tunnel with one or more learned address prefixes; and
in response to failure of the tail-end node, i) performing a penultimate hop popping (PHP) operation on traffic received along the TE-LSP at the PLR, and ii) rerouting the received traffic at the PLR onto an appropriate backup tunnel to an NNHOP corresponding to a destination prefix of the traffic.

### Claim 2 (depends on 1)

The method as in claim 1, further comprising:
computing a shortest path tree (SPT) rooted at the tail-end node to learn the address prefixes.

### Claim 3 (depends on 1)

The method as in claim 1, further comprising:
storing the learned address prefixes in a backup routing table (BRT) at the PLR.

### Claim 4 (depends on 1)

The method as in claim 1, further comprising:
storing the backup tunnels in a backup routing table (BRT) at the PLR.

### Claim 5 (depends on 1)

The method as in claim 1, further comprising:
ceasing to refresh the downstream state of the TE-LSP in response to failure of the tail-end node.

### Claim 6 (depends on 1)

The method as in claim 1, further comprising:
receiving notification that the TE-LSP is to be torn down;
tearing down the TE-LSP; and
tearing down the backup tunnel to each NNHOP in response to the TE-LSP being torn down.

### Claim 7

A system for protecting against failure of a tail-end node of a Traffic Engineering (TE) Label Switched Path (LSP) in a computer network, the system comprising:
one or more next-hop routers from the tail-end node (NNHOPs); and
a point of local repair (PLR) along the TE-LSP; the PLR adapted to
i) learn reachable address prefixes of the NNHOPs,
ii) create a backup tunnel to each NNHOP that excludes the tail-end node,
iii) associate each backup tunnel with one or more learned address prefixes, and
in response to failure of the tail-end node, iv) perform a penultimate hop popping (PHP) operation on traffic received along the TE-LSP, and v) reroute the received traffic onto an appropriate backup tunnel to an NNHOP corresponding to a destination prefix of the traffic.

### Claim 8 (depends on 7)

The system as in claim 7, further comprising:
a head-end node of the TE-LSP; and
a signaling message sent from the PLR to the head-end node, the signaling message indicating to the head-end node that the PLR is capable of protecting the tail-end node.

### Claim 9 (depends on 7)

The system as in claim 7, further comprising:
a head-end node of the TE-LSP; and
a signaling message sent from the PLR to the head-end node in response to failure of the tail-end node, the signaling message indicating to the head-end node that the PLR is currently protecting the tail-end node.

### Claim 10

A node for protecting against failure of a tail-end node of a Traffic Engineering (TE) Label Switched Path (LSP) in a computer network, the node comprising:
a network interface to receive traffic along the TE-LSP;
a memory adapted to store i) learned reachable address prefixes of next-hop routers from the tail-end node (NNHOPs), and ii) backup tunnels created to each NNHOP that excludes the tail-end node, wherein each backup tunnel is associated with one or more learned address prefixes; and
a processor adapted to i) perform a penultimate hop popping (PHP) operation on the received traffic, and ii) in response to failure of the tail-end node, reroute the received traffic onto an appropriate backup tunnel to an NNHOP corresponding to a destination prefix of the traffic.

### Claim 11 (depends on 10)

The node as in claim 10, further comprising:
a backup routing table (BRT) within the memory adapted to store learned address prefixes and backup tunnels.

### Claim 12 (depends on 10)

The node as in claim 10, wherein the processor is further adapted to learn the address prefixes reachable from the NNHOPs.

### Claim 13 (depends on 10)

The node as in claim 10, wherein the processor is further adapted to create the backup tunnels to the NNHOPs.

### Claim 14 (depends on 10)

The node as in claim 10, wherein the network interface is further adapted to receive state refresh messages for the TE-LSP from upstream nodes along the TE-LSP, and in response to failure of the tail-end node, the network interface adapted to return the state refresh messages to the upstream nodes without forwarding the state refresh messages downstream to the tail-end node.

### Claim 15

An apparatus for protecting against failure of a tail-end node of a Traffic Engineering (TE) Label Switched Path (LSP) in a computer network, the apparatus comprising:
means for learning, at a point of local repair (PLR) along the TE-LSP, reachable address prefixes of next-hop routers from the tail-end node (NNHOPs);
means for creating a backup tunnel from the PLR to each NNHOP that excludes the tail-end node;
means for associating each backup tunnel with one or more learned address prefixes; and
in response to failure of the tail-end node, i) means for performing a penultimate hop popping (PHP) operation on traffic received along the TE-LSP at the PLR, and ii) means for rerouting the received traffic at the PLR onto an appropriate backup tunnel to an NNHOP corresponding to a destination prefix of the traffic.