[mpls] draft-ihle-mpls-mna-stateless-egress-protection-00 - alternative approach

[Stewart Bryant <[e-mail]>]

An alternative strategy to encoding the alternate path labels “strangely” in the MNA header and then needing to construct a new stack by reformatting the MNA data into real labels is to have an MNA action : IF no repair POP n else ignore (or POP) action.


So the stack looks like

LSE to PLR
MNA Action POP n if no repair
LSE to C’
LSE to C’'
Etc

Note that delivery is not the only thing you need to worry about you need worry about the application labels which both egress nodes need to worry about.

So what happens

At the PLR it is determined if the link to C is up and C is alive.

If C is OK POP (or cleans) MNA header and the labels to the value n in its parameter. In the above case n = 2.

If C is not OK POP (or cleans) MNA header 

At this point we now have a set of LSEs at TOS that will execute the repair and get the packet to the alternate exit for C.

Note that the solution needs to consider what happens to the MNA header if more than one MNA action is present (proposed solution and this alternate) and what happens to application labels which need to be understood at C and the alternate to C.

This seems simpler and much more aligned with the existing MPLS architecture.

Best regards

Stewart