CRC Errors and Queue Drops - MTU Mismatch

Answered Question
May 9th, 2009

Hi.

We have a link with a provider which is exhibiting some symptoms which I've never seen before.

The interface is Gi0/3 on a 7200 router (NPE-G1). At the remote end, over a fibre link using RJ45 media converters, is a Cisco switch. I don't know what type of switch it is, as it is the provider's. From the provider's switch, they provide us a tunnel which pops out elsewhere.

I am seeing lots of CRC errors on my interface, a few runts and many queue drops on our interface. The provider has emailed me a show int and their end is fine (no errors, etc).

I suspected a duplex issue, but I am seeing no input errors or collisions. All I am seeing is CRCs and drops in the queue.

Anyway, the only thing I can see on the show ints from our router and the provider's switch is that my router has the MTU set to 1500, while the provider's interface is set to 1546.

Could the MTU mismatch explain the symptoms I am seeing, namely CRCs and queue drops? I am remote from the site and the link was only lit up a couple days ago, so I am unsure of any performance problems at the site.

Thanks

Matthew

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Correct Answer by Giuseppe Larosa about 7 years 6 months ago

Hello Matthew,

I would look at

>> over a fibre link using RJ45 media converters,

They can cause problems some times have it power cycled if possible.

CRCs should be input errors.

the mtu mismatch shouldn't cause the problems you see but it is something to deal with.

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Sat, 05/09/2009 - 22:20

Hello Matthew,

I would look at

>> over a fibre link using RJ45 media converters,

They can cause problems some times have it power cycled if possible.

CRCs should be input errors.

the mtu mismatch shouldn't cause the problems you see but it is something to deal with.

Hope to help

Giuseppe

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