[c-nsp] Tracking a dynamic default - supported?

Arie Vayner (avayner) avayner at cisco.com
Wed Sep 9 11:09:15 EDT 2009


This is a known issue documented in (internal) CSCta08772 and
Should be fixed in the next SRC (it is a recently fixed issue)


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of David Freedman
Sent: Wednesday, September 09, 2009 17:10
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Tracking a dynamic default - supported?

I can't find any information which would suggest that such a thing is an
unsupported configuration. Nonetheless, am unable to maintain a stable
track on a BGP default in 7200 12.2(33)SRC or 12.2(33)SRD (tested with
SRC2 and SRD2a)

#sh run | in track
track 20 ip route reachability

#sh track 20
Track 20
  IP route reachability
  Reachability is Down (BGP)
    5 changes, last change 4d14h
  First-hop interface is unknown

#sh ip ro
Routing entry for, supernet
  Known via "bgp 1234", distance 200, metric 0, candidate default path,
type internal
  Last update from 2d20h ago
  Routing Descriptor Blocks:
  *, from, 2d20h ago
      Route metric is 0, traffic share count is 1
      AS Hops 0

#sh ip ro
Routing entry for
  Known via "isis", distance 115, metric 300, type level-2
  Redistributing via isis
  Last update from on FastEthernet0/0, 2d20h ago
  Routing Descriptor Blocks:
  *, from, via FastEthernet0/0
      Route metric is 300, traffic share count is 1

#sh ip cef inte, epoch 0, RIB[B], refcount 5, per-destination sharing
  sources: RIB, DRH
  feature space:
   NetFlow: Origin AS 0, Peer AS 0, Mask Bits 0
   IPRM: 0x00018000
  path 65FF4264, path list 65FEA258, share 1/1, type recursive, for
IPv4, flags eos indirection, neos indirection
  recursive via[IPv4:Default], fib 66033BB0, 1 terminal
    path 65FF38E0, path list 65FE9C1C, share 1/1, type attached nexthop,
for IPv4
      MPLS short path extensions: MOI flags = 0x0 label implicit-null
    nexthop FastEthernet0/0, adjacency IP adj out of
FastEthernet0/0, addr 665F0B00
  output chain:
    loadinfo 65FD6C64, per-session, 1 choice, flags 0003, 164 locks
    flags: Per-session, for-rx-IPv4
    1 hash bucket
      < 0 > IP adj out of FastEthernet0/0, addr 665F0B00

The track is down most of the time, but changes state to up randomly
when there is no change in the network and for short periods of time.

If you track another prefix with a mask longer than /0 with the same
nexthop, stays up continually.

When labbing, I can demonstrate the issue in 12.2(33)SR but not in , for
example 12.3(M) in which the track works but is labelled "unsupported"

#sh track
Track 20
  IP route reachability
  Reachability is Up (unsupported)
    2 changes, last change 00:00:55
  First-hop interface is FastEthernet1/0

As usual, bugtool unhelpful.

Any ideas appreciated.

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