Technical data

Brocade MLX Series and NetIron Family Documentation Updates 35
53-1002805-03
Bypass LSP Liberal Path Selection
1
Bypass LSP Liberal Path Selection
TABLE 10 Supported platforms
Current algorithm
The current algorithm to select a Bypass LSP is very conservative. The restrictive algorithm can run
into situations where no backup path can be established. This can occur when bypass LSPs cannot
qualify under those restrictions, for example, under a less meshed topology such as single ring
topology.
The following process explains the steps of facility backup path computation, which involves
selecting the best qualified bypass LSP.
• Merge point selection: The PLR backup query process first selects in the order of preferred
merge point based on ingress signaled property. A merge point is selected in the order of
preference, from available bypass LSPs reaching this merge point. If no bypass LSPs qualify to
serve, move on to next preferred merge point. The merge point preference order depends on
the ingress signal with the node protection desired flag.
a. If node protection desired flag is present, PLR will go through merge point in the order of
next-next-hop (if present, to achieve node protection), next-hop (link protection), hops after
next-next-hop in sequence of traverse if any present.
b. If node protection desired flag is not present, the next-hop as the only merge point is
selected.
• Bypass LSP qualification: Bypass LSP cannot traverses any link attached to nodes traversed by
protected session between PLR and egress of LSP.
• If there is more than one bypass LSP qualified to serve for backup path, the lowest LSP cost
metric is considered. If more than one bypass LSP is available with lowest cost, the one with
the lowest number of riding backup sessions is selected.
For example, in Figure 3 on page 36, the FRR LSP path is: “A” to “B” to “C” to “D” to “G”. A Bypass
LSP is created at router B and the new path is: “B” to “E” to “G” to “D”.
In this example, the PLR is node B and the merge point (MP) is node D.
As per the current algorithm, the Bypass LSP traverses the link attached to LSP's egress node G.
Therefore, the Bypass LSP does not qualify to provide protection for the FRR LSP per the current
restrictive mode of the Bypass LSP selection/qualification.
Features
supported
Brocade
NetIron
XMR Series
Brocade
MLX Series
Brocade
NetIron CES
2000 Series
BASE
package
Brocade
NetIron CES
2000 Series
ME_PREM
package
Brocade
NetIron CES
2000 Series
L3_PREM
package
Brocade
NetIron CER
2000 Series
Base
package
Brocade NetIron
CER 2000 Series
Advanced
Services
package
Liberal
bypass LSP
selection
Yes Yes No No No Yes