MPLS TE FRR & some BFD

Question

Hi,
I have a few questions:
1. If you have TE tunnel with FRR configured for it, what will trigger the switchover to backup tunnel?
In my mind:
a. Link Protocol down on the interface
b. RSVP signalling
Now two other problematic ones are:
c. IGP neighbor down over a protected link (will it trigger TE reroute WITHOUT using FRR, so IGP neighbors and FRR would be two completely different approaches?)
d. BFD. Is it activated on a specific protected link or on the LSP headend (tailend) to "test" the end-to-end LSP? It is mentioned in BFD docs that when used with TE FRR it can report tunnel down BEFORE the tunnel having sufficient time to be rerouted (because BFD would be acting so fast). Does this mean BFD allows end-to-end LSP testing?
2. More about BFD. The docs say that BFD itself just reports to the protocol employing its services (like IGPs and maybe TE) that the connectivity betweem two points BFD is responsible for is down. If BFD is configured over an interface, does this mean that when BFD senses lack of reachability but Link Protocol stays up (like Ethernet), will it actually bring down the Link Protocol on that particular interface?
If not, it is unclear why would docs also say that BFD is best deployed with Interface Dampening. Interface dampening would work in case Link Protocol flaps...
Thanks!
David

Answer 1

Hi David,
Pls see my what i feel inline...
a. Link Protocol down on the interface
b. RSVP signalling
1(a,b)
Here again RSVP hellos are used as a trigger to achieve the FRR rather than relying on the line protocol to go down.
Which provides us fast upto 50msec protection.
Afaik TE FRR can utilize BFD as its relatively less resource intensive than generating RSVP hellos.
c. IGP neighbor down over a protected link (will it trigger TE reroute WITHOUT using FRR, so IGP neighbors and FRR would be two completely different approaches?)
1(c)
Without using FRR the TE reroute would be pure Tunnel Reoptimization based on your IGP convergence towards your Tunnel TailEnd.
d. BFD. Is it activated on a specific protected link or on the LSP headend (tailend) to "test" the end-to-end LSP? It is mentioned in BFD docs that when used with TE FRR it can report tunnel down BEFORE the tunnel having sufficient time to be rerouted (because BFD would be acting so fast). Does this mean BFD allows end-to-end LSP testing?
1(d)
"BFD can help test end-to-end data plane only just like LSP ping, but there is currently no integration of the results and mapping of the same to control plane in MPLS. hence BFD with LSP ping is being preached. More details can be found at http://www.ietf.org/internet-drafts/draft-ietf-bfd-mpls-03.txt."
2. More about BFD. The docs say that BFD itself just reports to the protocol employing its services (like IGPs and maybe TE) that the connectivity betweem two points BFD is responsible for is down. If BFD is configured over an interface, does this mean that when BFD senses lack of reachability but Link Protocol stays up (like Ethernet), will it actually bring down the Link Protocol on that particular interface?
If not, it is unclear why would docs also say that BFD is best deployed with Interface Dampening. Interface dampening would work in case Link Protocol flaps...
2.
No BFD would not involve itself into getting the link down, it will only enable the protocol bootstrapping or using it to declare a failure.
Now assume if the link is bouncing up and down, or there are intermittent losses because of link intergity. Then BFD would keep sending up down messages to the protocol employing it. Hence if the integration is with Dampening, then such UP or DOWN messages can be considered as flaps in the configured interval and the interface can be dampened. The Dampening as a process would utilize BFD triggers for calculating flaps rather than the Line protocol based UP or DOWN triggers. Thus enabling us to achieve the upto 50ms recovery time which is generally provided by POS/SONET with APS.
HTH-Cheers,
Swaroop