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New Member

3825 and 3845 router duplex issue?

We are currently having a new 10Mbps "LANLink" service installed in our office. Our WAN provider terminates in our comms room on a Lucent MUX, which then connects via RJ45 Ethernet to our Cisco 3825 router.

Our provider has asked us to set our router to 10Mb/full duplex. However, when we do, the Gigabit Ethernet interface on our 3825 goes down. If I set the interface to autonegotiate, it resolves to 10/half. Traffic will run at 10/half, but with muchos collisions.

We have exactly that same problem at the other end of the line, on a 3845 router. The router interface will only come up when running half duplex.

The engineer has been in and proved to me that the Lucent MUX is running 10/full. We have also switched out the ethernet cables a number of times.

We have stabilised the line somewhat by running all Lucent and Cisco equipment at half duplex. But surely there's a fix for this?

The interface config is shown below. Can anyone tell me what the 'negotiate auto' line means - despite 'speed 10' and 'duplex half' commands elsewhere?


interface GigabitEthernet0/1

description **Colt LANLink - London City Office**

ip address

duplex half

speed 10

media-type rj45

negotiation auto

service-policy output llq





Re: 3825 and 3845 router duplex issue?

Hi Richard,

When you have already configured speed and duplex settings I do not think you need "negotiation auto" as it is used to autonegotiate speed and duplex settings with the peer.



New Member

Re: 3825 and 3845 router duplex issue?

Hi Ankur -

Thanks for posting.

That's why I was confused - the 'negotiation auto' was already in the config when the router arrived. I don't see why it's even necessary: surely it's either 'duplex half/full/auto' and 'speed 10/100/1000/auto'? Why do Cisco need to provide another command for 'negotiation?