BT Internet Cisco 877 Router

We have a fairly large client all using Cisco 877 Router’s and all use BT Broadband (20mb) Recently we had a particular fault that went on for weeks at a single site and BT were determined it was not an issue with them. We tried an alternative router (Draytek, Linksys) and this held the connection without a problem.


The internet would drop between minutes, hours or days and was getting worse. When the connection was established it was showing a SNR of -1db so I knew there was a fault. You can view the noise by type “show dsl interface atm 0

Maybe the issue is to do with the Cisco 877 and I know they can be very sensitive. After some research and digging around I came across the 4.0.18 ADSL Firmware release from Cisco that specifically targets BT Internet. At first we were using the firmware that came with the 12.4 IOS range (3.0.14)

I updated the IOS to the 15.1.T IOS range which put the 4.0.17 Firmware on but the CD (Carrier Detect) light was still blinking and not detecting a signal. I loaded the 4.0.18 fix which can be downloaded from Cisco (Download Software –> Routers –> Branch –> 877 –> ADSL Firmware)


You need to rename the file to adsl_alc_20190.bin and place in the root of flash. Reboot the router and it will detect and automatically load this Firmware version. To verify run the “show dsl int atm 0” command to see the Firmware Version used.

After the reboot the Router CD light stayed solid and a healthy connection was made and the internet started working.

Note: Although Cisco say not to roll out this fix unless necessary we have done this to over 50 sites some with the issue and some with not and have not yet suffered a problem.

Any more information or help needed please contact me.

2 thoughts on “BT Internet Cisco 877 Router

  1. I’m also having an issue with a new Cisco 877 on a Deamon adsl2+ connection. It works for a short time then locks up with lots of CRC errors. The latest version on the cisco website only seems to be 4.0.17 for the adsl modem, I cant see the newer version 4.0.18 anywhere ?

  2. Just checked Cisco Site and it has actually been removed from their download list. Not sure why they have done this as we had terrible trouble with 40+ customers using a BT connection but as soon as the 4.0.18 firmware was applied and the router restarted connected up and held a solid connection with a good SNR (6.0Db+).

    Maybe they have incorporated or changed it in the latest IOS which has the 4.0.17 embedded but when we put the 15.T on it made no difference at all.

    I will send you over a link you can download the 4.0.18.

    Hope this helps

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