Track interface IP routing detects incorrect interface state

The track number interface name ip routing command is supposed to track an interface readiness to forward IP packets. In reality, it only tracks the interface line protocol status plus the IPCP status in case of PPP interfaces (as well as the actual presence of an IP address on the interface). If you configure IP Event Dampening (with the dampening) command, the interface might be suppressed (unavailable for IP routing), but the track object will report it as available (tested on IOS release 12.4(6)T). This could result in suboptimal HSRP/GLBP decisions if you use track objects to influence HSRP/GLBP priority or actual loss of data if you use such a track object to control policy-based routing.For example, with the following configuration ...

interface Serial0/1/0
dampening 15 500 2000 60 restart 500
!
track 1 interface Serial0/1/0 ip routing
... the interface might be suppressed while the track object would report it's up:
router#show interfaces dampening
Serial0/1/0
Flaps Penalty Supp ReuseTm HalfL ReuseV SuppV ...
0 3235 TRUE 42 15 500 2000 ...
router#show track 1
Track 1
Interface Serial0/1/0 ip routing
IP routing is Up
27 changes, last change 00:03:37
Tracked by:
1207165940

2 comments:

  1. what is the commands are configured under Giga interface to accomplis tracking ?

    ReplyDelete
  2. what if we just have dampening command under an ethernet interface?

    ReplyDelete

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Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.