Trunk issues with ping?

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Sep 5th, 2008
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I have a major problem. I have a catalyst 2950 to a catalyst 4006 via fiber. I can ping a normal size packet from one to the other, but when I use a datagram of 1500 it fails.. Would appreciate any ideas... repaced 2950 with two other switches and a new fiber patch cable to fiber box... 4006 moved to two other gbic locations..


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letsgomets Fri, 09/05/2008 - 11:11
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If you are indeed performing a ping over a trunk port then your packet size is exceeding ethernet boundries.


Depending on your encapsulation there is overhead on an ethernet packet for trunking. If memory serves me ISL is 30 bytes and 802.1q is 4 bytes

glynncounty Fri, 09/05/2008 - 11:12
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i am in the ios using the ping command to the other switch.. I can ping my other switches over the trunk with 1500 just fine to.



letsgomets Fri, 09/05/2008 - 11:17
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What is the largest datagram you set for the ping to work?

glynncounty Fri, 09/05/2008 - 11:16
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I understand that.. I can ping from my core to another switch with 1500 and no problem just to the switch giving us issues.

letsgomets Fri, 09/05/2008 - 11:30
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Perhaps you have jumbo frames enabled on those switches and not on the other one that doesn't ping?


Can you ping with smaller packets? If so then your problem is frame size. You can perform a packet trace and see exactly what size your frame is coming out of that interface.

singhsaju Fri, 09/05/2008 - 11:35
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Hello,


Use sniffer to capture ping packets on the trunk to see what's going on ??


HTH

Saju

Please rate if it helps

glynncounty Fri, 09/05/2008 - 12:11
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Figured it out.. Turns out the two gbic's where not the same manufacture which caused large issues... Changed over to Cisco GBICS and problem is now gone and can send a 1500 datagram size in ping.. Thanks for all the suggestions.

glen.grant Fri, 09/05/2008 - 12:13
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I know when you ping from a 4006 it will not let you use anything larger than 1472 , try that . Try 1472 or below. You are just pinging the mgt address so try to ping something else within that address range with 1500 . May be something with the 4006 supervisor or a restriction with catos.

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