Undersized Frame Issue

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Sep 28th, 2007
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I have a 3400ME 12CS 4SFP Metro switch connected to a 7606 Cisco router via a dot1q trunk port. On the 3400's port facing the 7606 I receive valid but too small of frames (or undersized frames). The 7606 shows RCV-errs because of the Input queue show that it has dropped numerous packets. I have tried new x-over cables, different ports on both devices, and changing from forced 100, full duplex to auto negotiate. I am getting stumped, I have setups like this in other locations and have compared configs with clean ones and nothing seems to be out of sorts. Any suggestions?

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htarra Thu, 10/04/2007 - 12:20
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This might indicate that this port is trunking dot1q and is receiving 64byte frames (including dot1q header).

Only impact should be that the counter increments. I think you have fixed the limit for queue. If it wills exceeded this no. it will drop the packet.

jcvassmer Thu, 10/18/2007 - 04:51
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Thanks to both of your responses I appreciate it. I replaced the 3400ME with a catalyst 3560 and the problem continued. The MTU sizes have been set to 1518 actually, and the problem continues.

cisconoobie Thu, 10/18/2007 - 06:00
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How is your trunk setup?

mode trunk or mode desirable? If mode trunk then switchport nonegotiate.

I had a similiar problem running an lacp etherchannel trunk. I switched it to mode on and it fixed the problem, but I'm guessing your running a normal non ec single link trunk?

jcvassmer Thu, 10/18/2007 - 06:49
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Here is the 7606 (WS-X6548-RJ-45) phy port config. It is set to trunk mode on as well is the 3400 trunk interface.

interface FastEthernet1/20

description Trunk to 3400ME GE0/10

no ip address


switchport trunk encapsulation dot1q

switchport trunk allowed vlan 2109,2116

switchport mode trunk

Again thanks for the input on this issue.


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