Why Won't This Trunk Come Up, Part 2

Unanswered Question
Apr 23rd, 2010
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Just wanted to bring back this discussion on manually setting the trunk parameters on two sides of a trunk and why it doesn't work.

The first time I did it was between two 3560s, and it didn't work.

Then I tried between a 3500XL and a 2960, and it didn't work.

Then I tried it today between a 2950 and a 2960, and it doesn't work.


1. Settings on each side:


Mode: Trunk

Speed: 100

Duplex: Full


(This config doesn't work)

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2. Settings on one side:


Mode: Trunk

Speed: 100

Duplex: Full


2a. Other side:


Mode: Trunk

Speed: Auto

Duplex Auto


(Results in duplex mismatch errors.)

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3. Settings on both sides:


Mode: Trunk

Speed: Auto

Duplex: Auto


(This works, negotiates full duplex and 100Mbps ethernet)

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Any ideas on why manually setting trunk parameters on each side, effectively disabling DTP, doesn't work?

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Jon Marshall Sun, 04/25/2010 - 14:50
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Nelson


I suspect this is to do with which cable you are using ie. cross-over or straight-thru and whether auto-mdix is enabled or not. I remembered reading about this a while back and have finally found the link i was looking for -


http://cciepursuit.wordpress.com/2007/07/08/switch-cabling-and-auto-mdix/


Jon

nelson.garcia Mon, 04/26/2010 - 11:10
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Jon, this looks exactly like what I need. I never really did use crossover cables for anything, figured you could use straight through cables for everything these days. I might also add that i tried trunking two 2950s with a default port config together and the link wouldn't come up, so I tried a trunk between a 2950 and a 2960 and it DID work. My guess is that the older 2950s just need a crossover cable because they might not have MDIX like the 2960 may?


Thanks for the link, Jon. I'll let you know if this works.

Jon Marshall Mon, 04/26/2010 - 11:25
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nelson.garcia wrote:


Jon, this looks exactly like what I need. I never really did use crossover cables for anything, figured you could use straight through cables for everything these days. I might also add that i tried trunking two 2950s with a default port config together and the link wouldn't come up, so I tried a trunk between a 2950 and a 2960 and it DID work. My guess is that the older 2950s just need a crossover cable because they might not have MDIX like the 2960 may?


Thanks for the link, Jon. I'll let you know if this works.


Nelson


Funny that because i do the opposite ie. i always use crossover cables but i think that means i'm a bit oldfashioned


Jon


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