FRR Facility

Fast Reroute Facility Protection

 The main principles of FRR Facility protection are similar to those

of the one-to-one method, with the following exceptions:

 FRR allows multiple LSPs that traverse the same set of hops to

be protected by the same bypass tunnel.

 The Merge Point selection is different.

 In case of a failure, traffic from multiple protected LSPs are

“tunneled” into the same bypass tunnel at the PLR.

 The PLR performs a “push” rather than a “swap” function (to

accomplish the tunneling).

 FRR Facility protection reduces the number of required protection

tunnels.

If multiple LSPs go through a certain shared portion of the network, they can all be protected by the same bypass

tunnel.

In order to accomplish this, the bypass protection tunnel must merge with the protected LSP at the closest point after

the point of failure.

In case of link protection, the closest point after the failure of the next link is the next-hop router along the protected

LSP-Path.

In case of router protection, the closest point after the failure of the next router is the next-next-hop router along the

protected LSP-Path.

In the example above, the LSP is configured with a facility bypass protection request. Node protection is disabled in

configuration, which means the routers should only attempt link protection.

Router R1 assumes the PLR role and triggers the bypass tunnel calculation process. On the resulting topology, after the

next link is pruned, the first router in the downstream direction is router R2. In other words, router R2 is the router on

which the forwarding of protected LSP traffic can resume right after the point of failure. Router R2 is chosen as the

Merge Point, and the link bypass tunnel is established to terminate on it.

The bypass tunnel established in this case can be identified with the name “bypass-link10.1.2.2” in the SR OS CLI

command outputs.

Using node-protect, MP is the next-hop router(R3) after the failed

router (R2). Router R3 is the next-next-hop for router R1.

 The protection tunnel is assigned the name bypass-node10.10.10.2

(the router avoided).

In the second example above, the facility bypass protection is configured with the default node protection request.

Router R1 again assumes the PLR role and triggers the bypass tunnel calculation process. On the resulting topology,

after the next router is pruned, the first router in the downstream direction is router R3. In other words, router R3 is

the router that the forwarding of protected LSP traffic can resume right after the point of failure. Router R3 is chosen

as the Merge Point, and the bypass tunnel is established to terminate on it.

Router R3 is also named as next-next-hop router in the RFC terminology.

The bypass tunnel established in this case can be identified with the name “bypass-node10.10.10.2” in the SR OS CLI

command outputs.

The complete and exact original primary LSP-Path hop and label

information is required for facility FRR.

 Next-next-hop and label information are also required.

 This information is obtained from the RRO of the RESV message

received on the primary LSP-Path

PLR routers require visibility over the exact path information

for the protected LSPs. This way, they can perform the Merge Point selection to establish the bypass tunnels. PLRs can

also decide if an already established bypass tunnel can be used for another LSP requesting Fast Reroute Facility by

analyzing its recorded route information.

This information is readily available in the Record Reroute Object. The recorded route information is also required

when forwarding the traffic from the original LSP-Path in the bypass tunnel when protection is active in case of a

failure.

NOTE: Recording is enabled on Alcatel-Lucent Service Routers by default. There is an option in the CLI to disable

recording as in the following example:

A:R1>configure router mpls lsp “to_R4” primary “fully_loose” no record

However, this is not a recommended practice because Fast Reroute cannot function in this case.

The SR OS CLI issues the following error if Fast Reroute is activated on an LSP with recording disabled:

A:R1>configure router mpls lsp “to_R4” fast-reroute

INFO: MPLS #1017 LSP parameter conflict - Cannot set 'fast-reroute' because 'no record' is already set on primary path

Guidelines for Establishing Bypass Tunnels in Facility FRR

 The main objective is to use the same facility bypass tunnel for

multiple LSPs.

 When an LSP requests Facility FRR, the router determines:

 Node-protect ― If it already has a bypass tunnel established

that avoids the next router.

 Link-protect ― If it already has a bypass tunnel established that

avoids the next link.

 If the required bypass tunnel is:

 Already established ― The LSP is associated to the same bypass

tunnel.

 Not yet established ― A new bypass tunnel is established and

the LSP is associated to it.

In order to accomplish this, the PLR router checks the Record Route Object (RRO) of the LSP that requests facility

bypass. Depending on the protection mode, the methodology of checking the RRO is as follows:

Node Protection: The PLR router checks the RRO of the requesting LSP and determines the next-next-node in the list.

The PLR then determines whether a bypass tunnel terminating on that router is already established. If it is, the new LSP

is also bound to that same bypass tunnel. The “protected LSP count” of the bypass tunnel is incremented to notify the

change.

On the other hand, if a bypass tunnel to the next-next-node does not yet exist, a new bypass is created. The LSP is

bound to the new bypass tunnel and the “protected LSP count” is set to “1”.

Link Protection: The PLR router in this case again checks the RRO of the requesting LSP and determines the next-node

in the list. The PLR determines whether a bypass tunnel terminating on the next-node is already established. If it is, the

new LSP is also bound to that same bypass tunnel. The “protected LSP count” of the bypass tunnel is incremented to

notify the change.

On the other hand, if a bypass tunnel to the next-node does not yet exist, a new bypass is created. The LSP is bound to

the new bypass tunnel and the “protected LSP count” is set to “1”.