[c-nsp] BFD expectations

[Jason Lixfeld]

On 2010-09-22, at 10:50 AM, Chris Evans wrote:

> Keep in mind that bfd is just a trigger method. You have to also take into fact that it still takes time for your protocols to converge.

Absolutely.  That's why I'm wondering if 2-3 seconds is realistic in the real world.

> What are your bfd timers set to?

The BFD timers are set to their lowest values:

bfd interval 50 min_rx 50 multiplier 3

Interesting thing is that bfd neigh det doesn't seem to reflect that:

c3600#show bfd neighbors  details 

NeighAddr                         LD/RD    RH/RS     State     Int
xxx.xxx.196.128                     6/6     Up        Up        Gi0/5
Session state is UP and using echo function with 50 ms interval.
OurAddr: xxx.xxx.196.129 
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
Received MinRxInt: 1000000, Received Multiplier: 3
Holddown (hits): 0(0), Hello (hits): 1000(562047)
Rx Count: 563901, Rx Interval (ms) min/max/avg: 1/1023/877 last: 598 ms ago
Tx Count: 562049, Tx Interval (ms) min/max/avg: 1/1549/883 last: 692 ms ago
Elapsed time watermarks: 0 0 (last: 0)
Registered protocols: ISIS
Uptime: 5d17h
Last packet: Version: 1                  - Diagnostic: 0
             State bit: Up               - Demand bit: 0
             Poll bit: 0                 - Final bit: 0
             Multiplier: 3               - Length: 24
             My Discr.: 6                - Your Discr.: 6
             Min tx interval: 1000000    - Min rx interval: 1000000
             Min Echo interval: 50000   

NeighAddr                         LD/RD    RH/RS     State     Int
xxx.xxx.199.184                       1/1     Up        Up        Gi0/2
Session state is UP and using echo function with 50 ms interval.
OurAddr: xxx.xxx.199.185   
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
Received MinRxInt: 1000000, Received Multiplier: 3
Holddown (hits): 0(0), Hello (hits): 1000(564093)
Rx Count: 566056, Rx Interval (ms) min/max/avg: 1/1023/879 last: 378 ms ago
Tx Count: 564095, Tx Interval (ms) min/max/avg: 1/1502/882 last: 464 ms ago
Elapsed time watermarks: 0 0 (last: 0)
Registered protocols: ISIS
Uptime: 5d18h
Last packet: Version: 1                  - Diagnostic: 0
             State bit: Up               - Demand bit: 0
             Poll bit: 0                 - Final bit: 0
             Multiplier: 3               - Length: 24
             My Discr.: 1                - Your Discr.: 1
             Min tx interval: 1000000    - Min rx interval: 1000000
             Min Echo interval: 50000   

This output is consistent on both the 7301 and the ME, so I'm thinking I must just be reading this wrong.

ISIS seems aware of BFD:

c3600#show clns neighbors detail 

System Id      Interface   SNPA                State  Holdtime  Type Protocol
c7301          Gi0/2       0016.9cb1.541a      Up     28        L1L2 IS-IS
  Area Address(es): 49.0001
  IP Address(es):  xxx.xxx.199.184*
  Uptime: 5d18h
  NSF capable
  BFD enabled
c7301          Gi0/5       0016.9cb1.5419      Up     29        L1L2 IS-IS
  Area Address(es): 49.0001
  IP Address(es):  xxx.xxx.196.128*
  Uptime: 5d17h
  NSF capable
  BFD enabled
c3600#


> How many prefixes? Etc....

Four.  The /30 connected to the test host on the 7301 end, the /30 connected to the test host on the ME end and the loopback addresses of the 7301 and the ME.

> > It's my understanding that BFD can provide failure detection and recovery similar to that found in POS. To that end, I'd like to use BFD with ISIS to design an L3 network that has failure detection and recovery mechanisms which rival L2 mechanisms like REP/G.8023/STP's various incarnations, etc.
> > 
> > I've labbed BFD+ISIS between a 7301 and an ME3600, run MTR between test hosts connected to each of the two devices and yanked one of the two links connecting the 7301 and the ME. I lose about 2-3 seconds worth of packets. Those results seem a little inconsistent with the claims of BFD's timing, unless there's something I'm missing and even with the BFD hooks, ISIS isn't able to react at near POS speeds.
> > 
> > Anyone have any perspective from the real world?
> > _______________________________________________
> > cisco-nsp mailing list cisco-nsp at puck.nether.net
> > https://puck.nether.net/mailman/listinfo/cisco-nsp
> > archive at http://puck.nether.net/pipermail/cisco-nsp/