Router with 2 ISPs

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Apr 17th, 2008
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I have a little difficult, i have 1 2811 with ios c2800nm-ipbase-mz.124-3g.bin, that receive a fiber from an ISP of 4.5Mb connected to a Fa0/0 and i have the switch of clients connected to the Fa0/1 using Publics and Private IPs, but I will receive in a few days a new Fiber with 3Mb from another ISP that will be connect it to Fa0/2. Then I will have 2 fibers in 2 Fastethernet just for internet then I need to configure load balance and the clients that use public IPs need to go through a specific ISP.

I have some ideas for do it but I don't know if will work, that's why I want some examples, comments or opinions if you can help me.



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Rick Morris Thu, 04/17/2008 - 12:09
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I assume these are two different ISP's.

You would want to run BGP. This will provide failover and some load sharing. In order to do this you will need your own ASN. This is a lengthy process, on avereage 30 days, so I would start now.

You will announce your IP networks out both peers. If your router has enough memory you can get full routing tables from them as well.

elelvis19 Thu, 04/17/2008 - 12:21
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Ok, I already know about how to do it with BGP but the problem is that i don't have time for the BGP and get the ASN and all that and our ISPs don't make that kind of configuration too often, then they can't do that perfect, I would like to do it without using BGP cause my router have low memory too, then is not appropriate using BGP.

If you know another way that can help me i will appreciate it.

Rick Morris Thu, 04/17/2008 - 12:31
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are the isp's the same or different?

One way is to break up your subnet and send 50% of the traffic out one link, and 50% out the other. Do this with static routes. Then provide weights for failover in case one link goes down all traffic will go out the stable link.

elelvis19 Thu, 04/17/2008 - 12:56
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They are two differents ISPs, that's a good idea break up the subnet in two parts but in the case of the private IPs i don't have how to say for example the network to go one part through one ISP and another one througt the second one i can't break up that network or don't know how, i'm using DHCP and NAT. I saw something in the web about use IP SLA but my router don't support that command.

Rick Morris Fri, 04/18/2008 - 03:40
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You would need to do Policy based routing.

If traffic enters the router from one subnet the traffic is inspected, by the policy, and sent out the link specified by the policy.

elelvis19 Fri, 04/18/2008 - 05:41
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Can you give me please an example of how to configure it to figure out if it is how i'm thinking.

I know is something like:


route-map [name] permit 10



interface [Fax/x]

ip policy route-map [name]


but i don't know exactly what to match and what to set it up.


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