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Router interface does not pass traffic.

Hi All,  we have a Cisco 3825 router which does not work well with a DSL  modem(ISP provided). I have configured the Gi0/0 port of the router to  plug into this DSL modem but it does not ping to the ISP gateway. If we  do a shut/no shut on the interface then it work fine for about 30 secs.  Sometimes even for 1 hr. Then the packets drop and we cannot pass any  traffic through this interface.

Now, if the ISP connection is terminated on a computer it works fine. It works fine without dropping any packet.

I  have tried various options like using a straight/cross cable. I have  tried to configure the interface negotiation for 100/full, 100/half,  auto/auto and almost all the options.

I have also tried to interconnect the devices using a L2 device like a HUB. Nothing works.

Any recomendation on this? Has anyone seen this kind of a behavior?


Nikhil Kulkarni.


can u check with the another Gi port if its working or not.

I have done that, checked even with a different router, switch, fast ethernet and Gi eth interfaces. It does not work.

With a PC it works. !!! this looks like there is some compatibility issues between the ISP modem and Cisco devices.



Hi Nikhil ...what is the IOS?


here goes the full sh ver:

rtr-vpn-kor-seo#sh ver

Cisco IOS Software, 3800 Software (C3825-ADVIPSERVICESK9-M), Version 12.4(15)T6,


Technical Support:

Copyright (c) 1986-2008 by Cisco Systems, Inc.

Compiled Mon 07-Jul-08 13:37 by prod_rel_team

ROM: System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)

rtr-vpn-kor-seo uptime is 1 hour, 48 minutes

System returned to ROM by power-on

System image file is "flash:c3825-advipservicesk9-mz.124-15.T6.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 3825 (revision 1.1) with 223232K/38912K bytes of memory.

Processor board ID FTX1101A1RL

2 FastEthernet interfaces

2 Gigabit Ethernet interfaces

1 terminal line

1 Virtual Private Network (VPN) Module

1 cisco content engine(s)

DRAM configuration is 64 bits wide with parity enabled.

479K bytes of NVRAM.

62720K bytes of ATA System CompactFlash (Read/Write)

Configuration register is 0x2102


show run int gig0/0

show int gig0/0

show run | in ip route

and what the settings we have on modem side for speed?hardcode or nego..?