eigrp and over utilized serial interface

[DARYLE DIANIS]

Can an over utilized serial interface or line cause eigrp to drop and lose adjacencies?  I have several routers that experience high utilization from time to time on their serial interface and the IXC claims that too much usage causes problems for eigrp and can cause the line to drop.   The lines are part of an mpls network.                   

[dslice]

"Can an over utilized serial interface or line cause eigrp to drop and lose adjacencies? I have several routers that experience high utilization from time to time on their serial interface and the IXC claims that too much usage causes problems for eigrp and can cause the line to drop. The lines are part of an mpls network."

I'm not completely sure what you're asking, but I'll attempt to answer your question anyway. If a link is so over utilized that packets are dropped, then EIGRP could certainly fall victim. Default timers for most interfaces mean that EIGRP sends hellos every 5 seconds and if three in a row get dropped, the peers go down. Is this what you're asking?

Sent from Cisco Technical Support iPad App

[John Blakley · Accepted solution]

If the excess traffic is causing the router to either miss hellos from the neighbor or the neighbor isn't receiving hellos from this router, then the neighborship can be torn down. Do you have any qos policies on the router? If not, you can try something like this to help:

class-map EIGRP

match protocol eigrp

policy-map Outbound

class EIGRP

bandwidth percent 5

class class-default

fair-queue

int

service-policy output Outbound

You should also do this on the other side....

HTH,

John

[Joseph W. Doherty]

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As the other posters have noted, a really congested link that's routinely dropping packets may cause issues for EIGRP (and other routing protocols).

Like John, a good solution is QoS that "protects" the routing protocol traffic.  What he has proposed would likely work, as just might using FQ alone.  (NB: you didn't describe your Cisco hardware/software, so what John wrote might not be supported.)

John's also correct, you often need to have QoS for both directions.  Since you mention MPLS, QoS is often available from such service providers.  Most of the time it needs to be requested.  Some service providers charge more for providing it.  (NB: non-MPLS service providers often don't offer QoS options.  Both kinds of service providers are often willing to sell you more bandwidth.)

Often another option is "tuning" the routing protocol to be more tolerant of a congested link.  Believe EIGRP supports such options.

[DARYLE DIANIS]

to all, thanks for your insight and suggestions.  It' makes sense and I'll look into adding some qos policy to protect eigrp.