Speed & Duplex Settings between 2901 Router and 2950 switch

Answered Question
Aug 22nd, 2010

Hello,

Today I have plugged in a new Cisco 2901 ISR G2 router into a Cisco 2950 switch.

On router side, the interfaces were hard coded to 100/Full and on the switch side all set to Auto.

On router, the commands SHOW IP INTERFACE G0/0 and G0/1

shows speed as 100 and Duplex as Full.

However on the switch SHOW INTERFACE STATUS

shows a-half and 10mbps.

Is it a normal behaviour?I feel in this case, the router too should have shown speed as 10mpbs and duplex as half.

Now on the switch I have hardcoded the speed/duplex to 100/Full.

I have this problem too.
0 votes
Correct Answer by Nagaraja Thanthry about 6 years 5 months ago

Hello,

Yes. You need to make sure that the effective speed/duplex settings are

supported by both ends. If there is a mismatch, you will start seeing

CRC-Errors and collisions.

Regards,

NT

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Nagaraja Thanthry Sun, 08/22/2010 - 02:27

Hello,

Since you have set the speed/duplex to 100/full on the router, it shows what

is configured. On the 2950, since it tried to negotiate and did not succeed,

it reverted to the default value. Please try setting speed/duplex settings

to auto on both devices and see if that helps. (It is especially helpful if

you have gig interface on one end and fastethernet on the other).

Regards,

NT

avilt Sun, 08/22/2010 - 06:03

How can I confirm the effective speed/duplex settings on the router itself?

Is it always by verifying on both the devices(switch and router)?

Nagaraja Thanthry Sun, 08/22/2010 - 08:21

Hello,

Typically, when you set it to auto negotiate, they negotiate to a value that

is supported by both hardware. Please take a look at the following links:

http://www.dell.com/content/topics/global.aspx/power/en/ps1q01_hernan?c=...

s=555&l=en&s=biz

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note...

6a00800a7af0.shtml#auto_neg_valid

Hope this helps.

Regards,

NT

avilt Sun, 08/22/2010 - 16:41

Thank You for the links.

However inorder to confirm the effective speed/duplex settings, do I always need to confirm on both the end(switch and router)?

Correct Answer
Nagaraja Thanthry Sun, 08/22/2010 - 16:58

Hello,

Yes. You need to make sure that the effective speed/duplex settings are

supported by both ends. If there is a mismatch, you will start seeing

CRC-Errors and collisions.

Regards,

NT

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