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Webcast-Catalyst9k
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One 1721 - Two ISP's

Hello,

I have a client whose office accesses all resources over the internet (hosted email, vpn, etc) and they have one T1 to the internet which goes down way too often.

If they get an additional T1 from a different ISP can the 1721 handle both? Multilink? Aggregating the bandwidth would be a bonus but the main goal is to have some sort of failover.

Could someone explain me how to accomplish this?

Thanks a lot,

Stephan

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Gold

Re: One 1721 - Two ISP's

Stephan

There are a couple ways to do it and each provides a slightly different result. To choose the better option you need to clarify what the customer's requirements really are. In the original post it implies that they are most interested in increased bandwidth. The way to achieve this is to have both T1s active and to have two default routes.

If the customer is really more interested in having a primary path and a failover path then you want both T1s active and a regular static default route and a floating static default route. It sould look something like this:

ip route 0.0.0.0 0.0.0.0 s0

ip route 0.0.0.0 0.0.0.0 s1 250

The 250 on the end of the second default route is an administrative distance and it means that as long as the primary default route is available it is in the routing table and is used. But if there is a failure on s0 then the route is removed from the routing table and then the route using s1 would be inserted into the routing table.

HTH

Rick

5 REPLIES
Hall of Fame Super Gold

Re: One 1721 - Two ISP's

Stephan

If the T1s are to different providers then multilink is certainly not an option. Increase in bandwidth for outbound traffic is possible by having two default routes, one to each provider. Increase in bandwidth for inbound traffic is tricky and partly depends on how much of the inbound traffic is response to things initiated from inside or how much is traffic initiated from outside.

I would think that a 1721 could handle both T1s.

HTH

Rick

New Member

Re: One 1721 - Two ISP's

Rick,

Thank you for the reply. If multilink is not an option then it is not a big deal. The main goal in their situation is to have a failover line and if the 1721 can handle 2 T1's to 2 ISP's then it looks like it would fix their problem.

So, if I put 2 default routes - one to S0 and one to S1 - how will the router choose between the two? Can I also set a prefered route (cost?) ?

Thanks again

Stephan

Hall of Fame Super Gold

Re: One 1721 - Two ISP's

Stephan

There are a couple ways to do it and each provides a slightly different result. To choose the better option you need to clarify what the customer's requirements really are. In the original post it implies that they are most interested in increased bandwidth. The way to achieve this is to have both T1s active and to have two default routes.

If the customer is really more interested in having a primary path and a failover path then you want both T1s active and a regular static default route and a floating static default route. It sould look something like this:

ip route 0.0.0.0 0.0.0.0 s0

ip route 0.0.0.0 0.0.0.0 s1 250

The 250 on the end of the second default route is an administrative distance and it means that as long as the primary default route is available it is in the routing table and is used. But if there is a failure on s0 then the route is removed from the routing table and then the route using s1 would be inserted into the routing table.

HTH

Rick

New Member

Re: One 1721 - Two ISP's

Rick,

Thank you very much!

The failover path is the main goal and the floating default route seems to be the best way to accomplish this.

Thanks again for your suggestions.

Stephan

Hall of Fame Super Gold

Re: One 1721 - Two ISP's

Stephan

I am glad that my answer was helpful. Thank you for using the rating system to indicate that your question was resolved (and thanks for the rating). It makes the forums more useful when people can read about a question and can know that they will read an answer that resolved the question. I encourage you to continue your participation in the forum.

HTH

Rick

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