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New Member

1721 router with T1 primary Internet and ADSL backup

I have a 1721 router with a WIC1DSU connected to a T1 for Internet. I would like to install a WIC1ENET in the other WIC slot and connect this to our ADSL providers router and configure that link as a backup for the Internet. I am having trouble locating info on how to configure this.

A collegue mentioned that if the ADSL and T1 are both provided by the same ISP that I can use OSPF. Otherwise I must use BGP, but first be sure that both providers support BGP protocol.

Is this true? Any sample configs or additional info would be appreciated as I've never configured a backup link.


New Member

Re: 1721 router with T1 primary Internet and ADSL backup

Note in this case, if the DSL goes down, the router won't know it - as far as it is concerned, its ethernet connection to the DSL modem is up. If you want the router to detect if the DSL is down, then put a WIC-ADSL in the router.

If you actually want to load balance, i would give BGP a shot. It is actually somewhat difficult to set up with different outside ip addresses on each interface - the routing and mapping issues are pretty nasty.

I just set up a configuration like this, with T1 and DSL on a 2620 router. I used route-maps for the NAT translation as well as policy based routing to direct traffic either over the T1 or the DSL

I can send you a cleaned up config file if that would be useful

New Member

Re: 1721 router with T1 primary Internet and ADSL backup

That would be great and much appreciated!!! So i realize the router won't know if the DSL goes down... but could I still configure the DSL connection as a backup rather than load balancing? Thanks.

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