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New Member

Fast Ethernet Duplex Issues

Dear Expert,

I was using the Cisco 2811 router, behind it having 2 FE port, when I try to change the mode of the duplex, from half to full, after that we do show interface, it indicate the interface is administrative down. This situation is very weird. Does anyone face this kind of situation before?


Re: Fast Ethernet Duplex Issues


Are you getting the interface down after making the duplex to full ?

did you see any error logs in your router regarding the same ?


New Member

Re: Fast Ethernet Duplex Issues

Dear spremkumar,

The status show the interface is administrative down, and the connection also lost as well.

sorry during that time forget to see the log.

Re: Fast Ethernet Duplex Issues


Can you post the config of the router and also the output of show ip int brief as well as show version ?


New Member

Re: Fast Ethernet Duplex Issues


sh version as below:

Cisco IOS Software, 2800 Software (C2800NM-ADVSECURITYK9-M), Version 12.4(8a), R


Technical Support:

Copyright (c) 1986-2006 by Cisco Systems, Inc.

Compiled Wed 19-Jul-06 23:21 by prod_rel_team

ROM: System Bootstrap, Version 12.3(8r)T7, RELEASE SOFTWARE (fc1)

xxx uptime is 3 days, 1 hour, 57 minutes

System returned to ROM by Reload Command

System restarted at 14:31:31 MY Fri Mar 30 2007

System image file is "flash:c2800nm-advsecurityk9-mz.124-8a.bin"

This product contains cryptographic features and is subject to United

States and local country laws governing import, export, transfer and

use. Delivery of Cisco cryptographic products does not imply

third-party authority to import, export, distribute or use encryption.

Importers, exporters, distributors and users are responsible for

compliance with U.S. and local country laws. By using this product you

agree to comply with applicable laws and regulations. If you are unable

to comply with U.S. and local laws, return this product immediately.

A summary of U.S. laws governing Cisco cryptographic products may be found at:

If you require further assistance please contact us by sending email to

Cisco 2811 (revision 53.51) with 249856K/12288K bytes of memory.

Processor board ID FHK0932F17M

2 FastEthernet interfaces

1 Virtual Private Network (VPN) Module

DRAM configuration is 64 bits wide with parity enabled.

239K bytes of non-volatile configuration memory.

62720K bytes of ATA CompactFlash (Read/Write)

Configuration register is 0x2102

sh ip inter brie as below:

xxx#sh ip inter brie

Interface IP-Address OK? Method Status Prot


FastEthernet0/0 YES NVRAM up up

FastEthernet0/1 YES NVRAM up up

NVI0 unassigned NO unset up up

For the configuration, sorry i can;t provide to you due to some company policy.

Re: Fast Ethernet Duplex Issues


Your interfaces is "up up". If it is as what you said "administratively down", it should show "administratively down down" or did you put it back to its original config or did you took the "show ip int brief" output from the wrong router?

New Member

Re: Fast Ethernet Duplex Issues

Exactly if you type the command you should see both of the Fa/0 interfaces adminis up/up.

You could maually shut the interface down and bring back up int fa0/0 no shut

fa/01 no shut

Then try the sh ip int br and they should come up

New Member

Re: Fast Ethernet Duplex Issues

To resolve the problem on the fa0/0 and fa0/1 interfaces, you need to use the "no shutdown" command in the interface mode.

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