Non-Stop ADSL with Cisco 1700 Router

[sanuk]

Hi,

I have a cisco 1700 router with:
- 1 ethernet (fastethernet 0)
- 2 ADSL WIC (atm0, atm1, dialer 0, dialer 1)
- running IOS ADSL/IP/NAT : c1700-y7-mz.122-15.t2.bin

I am crruntly using 1700 for ADSL (UK) internet connection sharing using ADSL-WIC-0.


|-----------|
| r 1700 |--(ADSL-WIC0) 121.x1.x2.x3
e0---| 2 nats |
| ? |--(ADSL-WIC1) 121.y1.y2.y3
|-----------|


Now bought a second ADSL connection and would like to configure the router in a manner that if 1st connection goes down, the internet must still remain available to the internal network using 2nd ADSL connection.

I have 1 real ip for each ADSL dialer interface (no internal global ip's) and a local static address for ethernet0.

Please help me with sample configuration, tips or advise, If you require current config, it can be provided.

I look forward to your earliest help.

Thanks,

San

 

[Frenchie2069]

The problem that you have is that the router will spoof the interfaces. If you do a show int d0 you will see:

Dialer0 is up, line protocol is up (spoofing)

This means that d0 will always appear in the routing table regardless of the state of the interface.

This is not to say it cannot be done - I have had a similar configuration (except that the backup was ISDN). I used a program called ServersAlive (

http://www.woodstone.nu/salive)

and the SATelnet check to monitor the status of the ATM interface. When the ATM interface went down I injected a route to the ISDN interface (and then removed it when the ATM interface came back up).

A much better solution would be to have a routing protocol (such as EIGRP) running across the two links so that the router could handle the routing table itself. However it will be hard to get most ISPs to do this for you. If you had access to a second router on the internet you might be able to create a tunnel interface, but I don't think that this would work...

HTH,
Michael.

 

[VanDykI]

Sorry to diverge, but I have the same thing basically, how do you inject a route into the routing table, and how do you clear the routing table?

Ian

 

[Frenchie2069]

Sorry, by inject a route, I meant add ip route x.x.x.x 255.255.255.0 y.y.y.y into the config.

Using SA and SATelnet you can monitor the status of the interface and then telnet to the router, add the static route, then remove it when the interface comes back up (all automatically). It is not an elegant solution, but it does work.

You cannot "clear" the routing table, the router automatically manages additon and removal of routes, depending on whether an interface is up or down or through a dynamic routing protocol like RIP, EIGRP or BGP.

HTH,
Michael.