[j-nsp] MPLS fast convergence without link information

[David Ball]

On 29 December 2011 11:48, Mark Smith <ggglabs0 at gmail.com> wrote:

> Correct me if I am wrong, but doesn't enabling BFD on the IGP cause
> IGP to reconverge in case of fault?

  yes

> Is there any (reasonable) way to utilize link-node-protection or FRR
> if link state information is not usable between MPLS routers? Or are
> these fast repair mechanisms only usable in case of dark fiber (or
> copper)?
> To put this in another way: I cannot expect sub-second recovery times
> unless the failure detection is triggered by interface link down?

  You should be able to get it close, yes.

> I had impression that one could use BFD to trigger facility backup
> (bypass LSP) in sub-second time (e.g. 3x 50ms). This appears to be
> incorrect.

  3x50ms is pretty low, but the idea is correct.  IGP with BFD and LFA
(loop free alternates) enabled, RSVP LSPs with facility backup turned
on and IGP configured to be able to use them as valid backup paths
('backup' knob under the LSP config, if memory serves).  Won't provide
you with 100% backup coverage for OSPF out of the box, but you could
tune your LSPs (if your network is relatively static in topology) to
ensure at least one of them is diverse from your IGPs primary path.

> I would not expect the L2 service provider to be able to tunnel
> ethernet OAM (CCM etc) traffic.

  See other respondents.  Provider and hardware dependent, though a
relatively decent QinQ implementation (if you're getting an EPL-like
service from your provider) might allow it. I know ours does.

> I wonder why haven't I found good information about this in the 'net.
> Am I blind or do all major players always have dark fibers (or
> similar) at their disposal? How about unidirectional fiber failures?
> At least in some cases (e.g. all autonegotiation stuff disabled)
> unidirectional fiber results in link up on the other (where rx sees
> light) end and link down on the other. How are these handled?

  Some others pointed out the caveats of using BFD in a link
aggregation scenario, but aside from that, you can go a long way with
BFD and LFA for your IGP running, potentially along with some specific
EROs for your LSPs to ensure your IGP has an available backup path in
the forwarding plane.

HTH,

David