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New Member

Dual ISP. How to configure failover in C1800?

Hello

I have a C1800 router. I want to connect this to my LAN and 2 different ISPS (on fa0 and fa1 respectively).

Which is the best way to configure the router for failover? I want all traffic to go to ISP A via fa0 as long as this ISP is up. But when A goes down I want all traffic to go via ISP B on fa1.

Both ISP A and B links might be either with dynamic DHCP-assigned IP-addresses or statically assigned addresses.

There is no incoming traffic to statically IP-addresses (like web-servers and such) to handle. This is just for outgoing internet traffic.

Best regards

Jimmy Larsson

7 REPLIES
Cisco Employee

Re: Dual ISP. How to configure failover in C1800?

Hi Jimmy,

Just 2 static default routes with different admin distance should work for you.

ip route 0.0.0.0 0.0.0.0 fa0 200

ip route 0.0.0.0 0.0.0.0 fa1 210

In this case all traffic will move out via fa0 only and once fa0 goes down second default static route with higher AD will become active for your all traffic.

HTH

Ankur

Re: Dual ISP. How to configure failover in C1800?

Hi,

Configuring floating routes via ethernet would not help out as the ethernet would always stay up.

Its better to get a default route from the service provider via BGP whom you want the traffic to be primarily routed and then add a floating route with 210 metric via the second provider.

regards

vanesh k

New Member

Re: Dual ISP. How to configure failover in C1800?

Hello

I am afraid that BGP:ing is not applicable. These routers is to be used as firewall/router at small offices world wide, often with xDSL-ISP:s. I am afraid I cant demand the ISP:s to talk BGP to us. ;)

/Jimmy

New Member

Re: Dual ISP. How to configure failover in C1800?

The problem is that the fact that ISP1 is malfuncional is not triggering fa0 to go down. And as long as fa0 is not link down the router will still route via fa0 even if the ISP has i.e routing problems a few hops away.

New Member

Re: Dual ISP. How to configure failover in C1800?

Another way to solve my original problem (it has to do with multiple DMVPN clouds for redundancy) might be to configure the router to route all traffic out via ISP A/fa0 EXCEPT traffic destinated to IP 2.2.2.2(which is my secondary DMVPN cloud HUB).

This will not make outgoing internet traffic work when ISP A fails, but my main goal is actually to always reach one of my 2 DMVPN Hubs.

How will this be configured?

Lets say that fa0 is addressed 5.5.5.5 and fa1 6.6.6.6. I have a default route to 5.5.5.1.

Traffic to my primary DMVPN hub 1.1.1.1 is routed via default route and 5.5.5.1 but I want traffic destinated to my secondary DMVPN hub 2.2.2.2 to go via fa1 and 6.6.6.1.

Is this accomplished with:

ip route 0.0.0.0 0.0.0.0 5.5.5.1

ip route 2.2.2.2 255.255.255.255 6.6.6.1

?

Regards

Jimmy

Re: Dual ISP. How to configure failover in C1800?

Hi,

If your ISP would not be able to do BGP , then auto fallback is not possible , u need to manually shut the interface for traffic to prefer the secondry path.

To explain abt ur doubt in ur routes , the fastethernet would not go down , so the ip 5.5.5.1 would always be reachable eventhough there might be a problem with physical link at service provider end .

regards

vanesh k

Gold

Re: Dual ISP. How to configure failover in C1800?

Try this document.

http://www.cisco.com/en/US/tech/tk364/technologies_configuration_example09186a0080211f5c.shtml

It uses a conditional policy route to select the path.

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