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Community Member

Trunk issues with ping?

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..

9 REPLIES
Community Member

Re: Trunk issues with ping?

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

Community Member

Re: Trunk issues with ping?

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.

Community Member

Re: Trunk issues with ping?

What is the largest datagram you set for the ping to work?

Community Member

Re: Trunk issues with ping?

Here is a good link for more information.

I should have said you can potentially reach Ethernet boundaries depending on your encapsulation choice.

http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080094665.shtml#frame1

Community Member

Re: Trunk issues with ping?

I understand that.. I can ping from my core to another switch with 1500 and no problem just to the switch giving us issues.

Community Member

Re: Trunk issues with ping?

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.

Silver

Re: Trunk issues with ping?

Hello,

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

HTH

Saju

Please rate if it helps

Community Member

Re: Trunk issues with ping?

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.

Purple

Re: Trunk issues with ping?

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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