Solved: Re: 3640 Fast Ethernet will not do Full Duplex

smintz · ‎06-20-2005

We have a 3640 with a NM-1FE1R2W connected to a Catalyst 4000. The configuration on the 3640 is set to duplex auto. The configuration on the Catalyst 4000 interface defaults to auto. I tried to force the interfaces to Full Duplex but the connection refuses to work in Full Duplex mode. The NM-1FE1R2W Token Ring interface is also configured and is connected. We can not figure out why this Fast Ethernet connection will not work in Full Duplex. Someone suggested it may be we aer also using Token Ring on the 3640 NN-1FE1R2W combo card. I did not find anything in the documemtation that would indicate that Full Duplex would not work if both if both FE and TR were used at that same time. Does anyone have an answer or any suggestions?

glen.grant · ‎06-20-2005

You shouldn't generally have a problem with 2 pieces of cisco gear auto negotiating ok as long as the code is fairly up to date on both , we have never had a problem with auto on a Cat 4000 and you should not have any problem when hardcoding both sides to 100/full duplex . We have 3600's and cat4000's working fine whether it be auto or hardcoding the speed/duplex . What does the 4000 say when you do a show port ??? Can you post both pieces of the port configs on both sides and may the show port on the 4000 and show int on the 3600 ? Also make sure the 3640 has the correct code levels running to support this card.

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Georg Pauwen · ‎06-20-2005

Hello,

I assume you have tried to set both sides simultaneously to full duplex ? TBH I have not heard of the interface only working in half duplex mode when the TR is used as well, but what happens when you shut down the TR interface ? Does the FE allow full duplex then ?

Regards,

GP

smintz · ‎06-20-2005

This is even more mysterious. I shut down the T/R. I was then able to establish Full Duplex on the FE by specifying DUPLEX FULL on both sides. DUPLEX AUTO will go back to Half Duplex. I then did a "no shut" on the T/R and it came up and the FE is still in Full Duplex. How can I verify the FE interface is really running Full Duplex?

Georg Pauwen · ‎06-20-2005

Hello,

weird indeed. You can verify what mode the interface is running in with the ; show interfaces' command...

Regards,

GP

glen.grant · ‎06-20-2005

Are you setting the speed also , even though it says FE these ports support 10 and 100 I believe and you can't set the duplex without setting the speed first . Set the speed as 100 then the duplex as full . you have to do this on the 4500 also you can't just use the duplex command .

smintz · ‎06-20-2005

yes, both the speed and duplex are set by configuration command. Are there some cisco interfaces that do not auto negotiate correctly? The 4500 is quite old but I would have thought the 3640 was recent enough to work.

glen.grant · ‎06-20-2005

You shouldn't generally have a problem with 2 pieces of cisco gear auto negotiating ok as long as the code is fairly up to date on both , we have never had a problem with auto on a Cat 4000 and you should not have any problem when hardcoding both sides to 100/full duplex . We have 3600's and cat4000's working fine whether it be auto or hardcoding the speed/duplex . What does the 4000 say when you do a show port ??? Can you post both pieces of the port configs on both sides and may the show port on the 4000 and show int on the 3600 ? Also make sure the 3640 has the correct code levels running to support this card.

smintz · ‎06-20-2005

I had a problem with another connection to the 4000 only working in half-duplex. By forcing the speed to 100 1st, the full duplex now works. Now I have some doubts about how I had the 3640 interfaces set. I may not havde had the speed set on those either. It works now so thanks.

scottmac · ‎06-20-2005

Problems getting the system to 100/full are most often related to the cabling.

If the cables are handmade, and not pinned-out according to the 568a or 568B standard.

If the cables were pinned out like , then you create a "split pair" on pins 3&6 (meaning that the tx of one colr is working with the rx of another color ... you lose the "twisted" pair benefits .... like crosstalk supression).

You can't even force it to work, because the near-end and far-end crosstalk is som bad, the NIC either fails to communicate, or "downshifts" to something acceptable.

Working at 10 (even working at 100 half) but not at 100 full is a hallmark symptom of a split pair 3-6.

If the cables are commercialy produced, check them for wear & tear, kinks, twists, crushed jackets, jacket hanging out of the connector (no strain relief) ... all can produce the symptoms you describe.

Cabling is the foundation of the network: if your cabling sucks, then the network performance (if it works at all) will also suck. It's the most important component of the network ... without good, fully-functional cabling, nothing is going to work at best performance.

I know that the topic is checked as "solved" but it's still something you need to keep in mind. Perhaps others are having similar problems that are actually cabling related.

FWIW

Scott