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Internet fail over using DSL

Currently our organization uses a standard Cisco solution using a 3640 and T1 to an ISP. Someone in our company took it upon there self to order ADSL from Ameritech under the understanding that it could be used for automatic fail over for Internet traffic. The ADSL is just Internet. It has been a while doing routing for myself, I need to try and make this work. Here is what I can tell you. Our border 3640 has two Ethernet ports and a T1 wic. The Ameritech DSL uses an Efficient 5861 router I assume we will get a DHCP address from Ameritech. I will just use Fa 0/1 on 3640 to Ethernet on 5861.

Can anyone forward configurations used to do? I’m confused on trying to use just static routing, but I feel that I’m going to have to use BGP.


Re: Internet fail over using DSL

Shouldn't need BGP. As far as the failover piece, depending on how your have your primary routing to the internet set up, you can modify the administrative distance of the path thru the dsl link to be less attractive. Should the primary fail, then this becomes the preferred path.

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Re: Internet fail over using DSL


It's called floating static routes.

The lower metric static will point to your T1.

The higher metric static will point to your DSL.

If T1 fails, the route is removed from the route table, and the DSL route takes over. Once the T1 is comes back up, the T1 route is inserted back into the route table, and traffic will use your T1.

Keep in mind that this is not stateful failover. And, you may want to look into setting up secondary Mx records and DNS records if you are running any services so that if the T1 fails, incoming traffic can use the DSL.


T1 --> ip route 1

DSL--> ip route 5

Oh, if you are a business, I think your only option is DSL w/ Static IP's. The dynamic IP's use PPPOE and is only for home use...

From my limited understanding of the SBC DSL offerings in Ameritech/PacBell regions.



Community Member

Re: Internet fail over using DSL

Failover is a much easier scenario to deal with than load balancing.

Keep in mind that if you use the Efficient modem, the 3640 will never detect the DSL line going down.

in order for the router to know if the DSL line is down, you will need to install the ADSL WIC card into the 3640, if there is a slot left and if the 3640 supports ADSL WIC cards (I don't know the answer to either).

In your case you are using the T1 as primary and DSL as backup, so you may not really even care if the DSL line bounces up or down.

You probably have address blocks from both providers. Some have suggested to me trying to get each of them to advertise routes to the other's address blocks, but try calling SBC Internet Services and talking with someone who will know what the heck you are talking about...

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