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Changing interface bandwidth affects EIGRP availability?

Today I was told changing interface bandwidth will cause interface flapping. I am unable to repro. Is there any platform on which changing interface bandwidth causes traffic interruption with EIGRP? AFAIK I don't think it has impact on availability with OSPF.

For EIGRP if metric is increased and no FD available, it will result in queries for affected prefixes. I am not seeing how that would impact availability tho.

2 Replies 2

Paul Chapman
Level 4
Level 4

Hi -

I can't recall a situation where modifying the bandwidth statement on the interface caused an interface flap.  The bandwidth statement only impacts processes in the router that use it as a basis for calculations (EIGRP, OSPF, QOS, FabricPath, etc...).  Even if a recalculation results in modification of the traffic flows, you still don't get an interface flap.  The traffic just migrates to the desired path (or hopefully the desired path).  Worst case scenario with your routing protocol is that you send traffic down a low bandwidth link by accident.

HTH and Good Luck!

PSC

For multipoint WAN links, such as a single-subnet WAN connection spanning multiple sites, bandwidth must be set to the same value even if the CIR or physical interface physical speeds differ. For example, if HQ has 1 Gb of BW, Site 2 has 250 Mbps, and Site 3 has 100 Mbps, and you set each bandwidth to its correct value, you get EIGRP timing issues between neighbors of different CIRs.

I know this from experience with my new ASR and ISR44XX's. I'm pretty sure I've narrowed in on the solution, which is to lower bandwidth setting to 100 Mb for all sites. Has anyone had any experience with a situation like this?
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