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Webcast-Catalyst9k
New Member

100M auto duplex

hi guys,

we have a router and setup the negotiation to auto, the carrier DSU is supposed to be 100M full, however the interface won't come up.it only comes up if we change the negotiation to the router to half.And when it is auto, it becomes half, from my understanding if is auto and becomes half on the sh int output, it means the device at the other end is half, is that right?

It also doesn't come up with full duplex.

Am assuming the cause is because the carrier DSU is configured in half, not full.

otherwise, please advise if there's any portion we should check or do or possibly missing?

Thanks

10 REPLIES
Cisco Employee

Re: 100M auto duplex

Hello,

It is possible that the carrier DSU's ethernet port is statically set to 100 Mbps, full duplex. In this case, its autonegotiation capability may be deactivated completely.

Have you tried to set your Cisco interface statically to the same speed and duplex? Setting a duplex mode statically should not cause a link to go down or up but if duplex mismatch happens, you will notice large numbers of collisions on the interface.

So try to set both the speed and the duplex statically and see what happens.

Best regards,

Peter

New Member

Re: 100M auto duplex

Hi Peter,

the carrier DSU should be 100M full, and we're assuming it is...however the router port only comes up when it is half, and when we change it to auto, it becomes half...

Cisco Employee

Re: 100M auto duplex

Hello Jayson,

Let me ask once again... you are saying that the following configuration does not work:

interface Fa0/0

speed 100

duplex full

while the following works:

interface Fa0/0

speed 100

duplex half ! or duplex auto

Can you please confirm this?

Best regards,

Peter

New Member

Re: 100M auto duplex

Thanks Peter

DSU:

interface Fa0/0

speed 100

duplex full

router:

interface Fa0/0

speed 100

duplex half ! or full=NG

duplex auto=it goes up but it becomes half

Cisco Employee

Re: 100M auto duplex

Hello Jayson,

Quite unusual behavior, hmmm... Have you tried connecting any other device to the DSU? A different port on the router, a laptop, a switch perhaps - simply a different device to see if it links with 100Mbps/FD?

What would happen if you tried the following configurations?

int Fa0/0

speed auto

duplex auto

and

int Fa0/0

speed auto

duplex full

Can you tell me what effect do these configurations have?

Best regards,

Peter

New Member

Re: 100M auto duplex

unfortunately, got no access to the DSU, only to the router

Cisco Employee

Re: 100M auto duplex

Jayson,

I meant to test those configurations on your router, not on the DSU. And are you saying that you can't unplug the cable from the router and plug it into a laptop?

Best regards,

Peter

New Member

Re: 100M auto duplex

nope...the device is on a remote site

Cisco Employee

Re: 100M auto duplex

Jayson,

I see. Well, either we need to make ourselves some room to make a few additional experiments or we depend on the ISP and his ability to diagnose the DSU.

Personally, when it becomes feasible, I would suggest connecting another device to the DSU to see how does it link with it. I would prefer a Linux laptop as you can see quite a lot of useful debugging info and you have also a good access to the autonegotiation process - but I believe that anything will do. If you can confirm that with various devices, they have linked with the DSU only on 100M/HD, that would be a persuasive argument for your ISP. Otherwise, if these devices are able to go on 100M/FD and perhaps without any additional configuration then this is more serious and I would contact the TAC about the recommendations how to proceed. I am aware of a few incidents where Cisco's Ethernet interfaces had troubles linking with other vendors' equipment.

In any case, please let me know how does this case proceed.

Best regards,

Peter

New Member

Re: 100M auto duplex

Try changed the cable first.

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