Cisco 2800 ADSL Failover

[parmstrong5]

Hi, am having trouble trying to setup a 2800 series router as a failover device (please bear in mind that I am fairly new to IOS).

The device has two ADSL modules installed which will be used as a direct connection to the ADSL lines rather than go through a seperate modem.

I am looking for the config so I am able to connect to either connection and should the primary connection fail the secondary connect takes over.

I have been trying to configure this on and off for a while however am struggling even to get the router to successfully connect to the ISP.                

[Peter Paluch]

Hello Mithun,

You are welcome. No harm was done, and I also sincerely hope I did not offend you.

I am well aware that the three commands mentioned above would not cause any harm (apart from ip mtu 1492 which would cause unnecessary fragmentation). Then again, those are commands I see again and again in recommended configurations simply because they once got into examples somewhere at Cisco website and there was nobody to fix them. Even if a command does not do any harm, you ascribe a certain meaning to that command, and when you try to reuse the command in a different environment hoping it does what you think it does, you may end up being surprised very unpleasantly. That is one of the reasons I am always vouching for a very clean configuration free of commands that have no usefulness.

Best regards,

Peter

[parmstrong5]

Hi Peter (thanks for the massive help so far, believe we can see light at the end of the tunnel).

Fixed the DHCP pool error and am now able to get traffic moving between the computer and the Internet through the Dialer1 connection.

However when trying the Dialer2 alone it does not allow any data past the router.

Tried a tracert as requested on the working connection went through 16 stops.

I am having to test this early morning due to connections being use for an existing network during normal working hours, this is why there has been long(ish) pauses between replies.

[Peter Paluch]

Hi Phil,

You would actually need to shutdown the Dialer1 interface in the configuration to see if the communication can get through via the backup DSL connection. The reason is that the Dialer interface state does not reflect the state of the physical DSL line, so even if the primary ADSL connection goes down, the Dialer interface remains up and the default route is still kept via the first provider.

So please try to do the experiment by adding the shutdown command to Dialer1 and see if the internet connection still works (you may pull out the primary DSL link to be absolutely sure but the shutdown command is the key here). If it is, let me know, and I will try to prepare a configuration for you that performs the active test and brings up/down the default route as necessary.

Best regards,

Peter

[parmstrong5]

Yeah this is the case, second DSL connection is actually faster so will alter the dialer settings to make this the primary connection.