Facility Backup

In tihs case all the protected LSP 's in the same network segment share the same bypass tunnel.

Facility bypass reduces the number of bypass tunnels required to provide protection to the main LSP

Facility bypass tunnel cannot be used as a backup for those LSP which are configured with a reservation style of FF.

When a failure of a link occurs traffic from multiple LSP;s are rerouted by the PLR through the same bypass tunnel.

When the traffic reaches the MP router it merges the traffic back to the primary LSP, in order to achieve this purpose the MP router must be aware of the LSP's in which each flow belongs to. Favility bypass tunnel takes advantage of the MPLS label stack and uses a third label to encapsulate  the protected traffic and carry it through the bypass tunnels.

The following is seen when facility backup is used:-

When the PLR reroutes the traffi c away from the local failure, it keeps both
labels in the protected traffi c’s MPLS label stack. It pushes the third bypass
tunnel label to re-encapsulate the protected traffi c and then sends the traffi c over
the bypass tunnel. The protected traffi c now has one more label in the MPLS
label stack, the bypass tunnel label on the top.
• All routers along the bypass tunnel swap only the top bypass tunnel label to
switch the traffi c toward the termination point of the tunnel. The protected
traffi c is tunneled from the PLR to the MP router; this is why the protection tunnel
used by FRR facility backup is called the bypass tunnel.
• At the termination point of the bypass tunnel, the MP router fi rst pops the
bypass tunnel label to expose the original traffi c. Then, the MP identifi es the
original LSP-Path by examining the outer labels (MPLS transport label) and
merges the traffi c back to the correct protected LSPs.

The bypass tunnel is used for a multiple LSP hence each of them uses its own tunnel-id and LSP-id.

The

facility bypass uses the Near-MP approach:

• For link protection, the bypass tunnel originates at the PLR and terminates at

the PLR’s NHop router. The MP is always the NHop router of the PLR.

• For node protection, the bypass tunnel originates at the PLR and terminates at

the PLR’s NNHop router. The MP is always the NNHop router of the PLR.

Thus, LSP-Paths can share the bypass tunnel providing their paths go through

same PLR and MP.

When an HE router has an LSP confi gured with facility backup desired, the HE

router sends a PATH message indicating this by:

• Adding the

set (

• Setting the

FAST_REROUTE object having the facility backup desired fl ag0x02)SESSION_ATTRIBUTE object’s fl ag of local-protection-desired

bit to 1. If node protection is desired, it will also set the

node-protection-desired

not have a fl ag indicating node protectionbit to 1. The FAST_REROUTE object does
Once it receives the path message from the HE router all the routers assume the PLR role and start to establish bypass tunnels

The path message of each of the PLR when they assumed the role of the PLR has the following items:-

Fast Reroute object:- This contains the ip address of the PLR and the ip address the detour LSP  is trying to avoid.

In the

format of

As an example, the bypass tunnel name of

this tunnel is providing a link protection for the link with one side’s IP address 10.117.118.1. All LSPs desiring link protection on that link, by that particular
IP address, can share this tunnel.

Once established the bypass tunnel becomes a common facility and can be used by many LSP traversing the path hence the name bypass.

SESSION_ATTRIBUTE object, the name of the bypass tunnel is set to thebypass-{link|node}{IP address of the protected object}.bypass-link10.117.118.1 means that