Ping timeouts from 2621XM router to 2900 cat switch

vimal.nanthacumar · ‎11-23-2004

I have this weird issue on the network where when I ping from router(2924XM IOS 12.2) to the 2900 switch management ip address (IOS 12.1) with 1500 bytes, I am getting timeouts. When I ping across the WAN to the management ip address of the switch it sucessful without any timeouts. I have no ACL or any security enabled on the router or the switch.

Has anyone see this type of issue before?

glen.grant · ‎11-23-2004

some switches won't allow 1500 byte pings , only like 1472 due to overhead . Have you tried like 1400 byte pings ?

vimal.nanthacumar · ‎11-23-2004

I tried this already. Anthing over 121 byte pings I get a timeout. Weird!!!. Please let me know if you have any other suggestion.

Thanks,

Vimal

Kevin Dorrell · ‎11-23-2004

That is indeed strange. I cannot say why it is happening, but here is my train of thought:

I wonder whether 121 gives us a clue: perhaps 121 upwards fails and 120 is OK? So what would be 8 bytes long - the only thing I can think of is the ICMP header itself. (I presume the 120 is the payload, excluding the ICMP header.) That gives us a nice round 128 byes maximum payload on the IP packet - 148 including the IP header. 128 looks much more like a limit than 148. So it looks like an IP-layer fragmentation problem or MTU. Why should the IP layer be limiting its payload to 128 bytes? I don't know. It's like you had an X.25 link on the way, but I don't really believe that is it.

Sorry, I cannot solve it, but I hope the thoughts turn out to be useful.

Kevin Dorrell

Luxembourg

robphill · ‎11-24-2004

Vimal,

Open up a case with Cisco TAC I seem to remember a bug regarding the 2900 XL series switches responding to ping sizes of certain sizes not working due to software.

glen.grant · ‎11-24-2004

Can't say we have ever seen this on any of our 2900XL's and we have a lot of them , the old 4 meg and the 8 meg boxes . you can try upgrading it if you have the license . Can you post the switch and router config minus any addresses ??? also you said the 2900 was 12.1 , as far as I know the 2900's never went above 12.0 .