ME3400 to ASA5510: Stubborn Duplex Mismatch

Unanswered Question
Aug 2nd, 2008

Hi, all. First off I must admit I'm a newbie when it comes to the Cisco routing & switching. I'm learning, so please bear with me if I miss something that's painfully obvious to the more experienced, hehe. Here's the problem:

We have an ME3400-TS metro switch that connects our 3845 router and our ASA5510. Fa0/22 on the 3400 connects to ethernet0/0 on the ASA, which is the outside connection on the ASA. Well, fa0/22 seems to be taking a load of errors and dropping connections (LED flashes amber every few seconds). After checking out the interfaces I see that fa0/22 on the 3400 is running 100Mb/half-duplex while ethernet0/0 on the 5510 is running 100Mb/full. Hey! No problem! Just force them both to 100Mb/full, right? Negative, hehe. The connection goes down completely if I do that. The only way to get them talking again is to set them both to auto speed/duplex, but, of course, the mismatch errors start again. Any suggestions would really help bail me out. Thanks very much!

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Mark Yeates Sat, 08/02/2008 - 16:20


Have you tried hard coding the settings on both sides to where they will work?

Try hard coding using one of these settings.






Farrukh Haroon Sun, 08/03/2008 - 23:38

Keep the ASA side to auto/auto. Then change the switch to 100/full or auto/auto or auto/full. If the switch is going to half then it means it is unable to negotiate, so it 'guesses' the speed and 'plays safe' with the duplex. Also is this a straight-through cable you are using?




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