Technical data

36 Brocade MLX Series and NetIron Family Documentation Updates

53-1002805-03

Bypass LSP Liberal Path Selection

FIGURE 3 Bypass LSP

New algorithm

The new facility backup computation mode applies an algorithm between and extremely

conservative approach and an extremely liberal approach. The changes only affect how a bypass

LSP is qualified. There are no changes regarding the merge point selection or capability to disable

providing node protection or tie breaker from multiple qualified bypass LSPs.

For a bypass LSP to qualify for the backup path, it must pass following tests:

• Bypass LSP cannot traverse any nodes between PLR and merge point if there are any

Using the example above (Figure 3 on page 36), the new algorithm mandates that the Bypass LSP

cannot traverse node C.

Therfore, with the new Bypass LSP selection mode turned on, the above Bypass LSP qualifies and

can be used to provide protection for the FRR LSP.

Enabling bypass LSP liberal path selection

The cspf-computation-mode command enables or disables backup query algorithm using minimum

restrictions to qualify the bypass LSP. This command can be executed on the fly and bypass LSP

selection process will use the restricted or liberal mode, depending upon the current configuration.

Changing the computation mode on the fly will not impact the already selected bypass LSPs. This

configuration is equally applicable to dynamic bypass LSP selection as well.

To enable the liberal bypass LSP selection, enter the following commands.

Brocade(config)# router mpls

Brocade(config-mpls)#policy

Brocade(config-mpls-policy)#cspf-computation-mode use-bypass-liberal

Node

PLR

Link1

Node protection

Protected LSP used Links

–

rotected interface

Bypass LSP Path

Protected

LSP Tail

Protected

LSP Head

Facility Protected LSP

Backup path from PLR to MP.