Dialer-watch behaviour..

[tom.storey]

Im experiencing some (strange?) behaviour with a dialer-watch setup I have running on an 1801 router.

I have an ADSL service backed up by an ISDN service.

Essentially the failover works fine, but the problem is with the "failback" to the ADSL service when it comes back. Im testing this in a lab environment at the moment.

Due to the fact that Dialer interfaces never go down, I cant add two default routes via each Dialer interface, otherwise the default route with the lower metric (i.e. via ADSL) is ALWAYS in the routing table regardless of whether the ADSL service is up or not. So what Ive done to get around this is:

ip route 0.0.0.0 0.0.0.0 203.34.x.129 10

ip route 0.0.0.0 0.0.0.0 Dialer1 20

The first route is via the IP of the NAS that the ISDN service lands on, and the second route is via the Dialer interface of the ADSL service. This works very well. When ADSL is up and ISDN is down I have a default route via ADSL, and when the ISDN comes up, presumably because of a failure of the ADSL service, I have a default route via the ISDN service.

At present I have the following dialer-watch configuration:

dialer watch-list 2 ip 150.101.x.4 255.255.255.255

dialer watch-list 2 delay connect 5

dialer watch-list 2 delay disconnect 10

This is sufficient to bring up the ISDN service when I pull the phone cable out of the ADSL port on the router, at which stage I end up with a routing table such as this:

203.34.x.0/32 is subnetted, 1 subnets

C 203.34.x.129 is directly connected, Dialer2

59.0.0.0/29 is subnetted, 1 subnets

C 59.167.x.168 is directly connected, Vlan1

150.101.0.0/32 is subnetted, 1 subnets

C 150.101.x.48 is directly connected, Dialer2

S* 0.0.0.0/0 [10/0] via 203.34.x.129

Whel I plug the phone cable back into the ADSL port and ADSL comes back up I have the following route table:

203.34.x.0/32 is subnetted, 1 subnets

C 203.34.x.129 is directly connected, Dialer2

59.0.0.0/29 is subnetted, 1 subnets

C 59.167.x.168 is directly connected, Vlan1

203.16.x.0/32 is subnetted, 1 subnets

C 203.16.x.223 is directly connected, Dialer1

150.101.0.0/32 is subnetted, 2 subnets

C 150.101.x.4 is directly connected, Dialer1

C 150.101.x.48 is directly connected, Dialer2

S* 0.0.0.0/0 [10/0] via 203.34.x.129

Theoretically after 10 seconds of this happening the backup interface should go down (as is my understanding) and default routing should resume via Dialer1 over ADSL.

The problem I have is that the backup interface does not go down, and traffic continues to be routed over the ISDN service.

Am I incorrect to assume that dialer-watch doesnt take down a backup interface once the primary interface comes back? Will the backup interface not go down until there is no traffic running accross it?

If this is the case it will never go down because my default route via ISDN will always have precedence due to its lower metric. But I have no way around this because my ISP has multiple LNS's that I could land on, each presenting its own IP.

Any ideas?

[tom.storey]

I also thought I might post the log of events when the ADSL service goes down, and the ISDN comes up, and then when the ADSL service comes back up. This clearly shows the primary interface being marked as DOWN, and then UP which should trigger the 10 second delay before disconnecting the backup link.

(This is the output from having "debug dialer" and "debug dialer events" turned on)

** Please see attachment **

Cheers! :-)

(I figured a lot of information is better than not enough)

[tom.storey]

I thought I might also include the config of my router at this stage.

Any help appreciated.

[tom.storey]

And an even better solution to this is to add:

ppp ipcp route default

to the config of Dialer1, and:

ip route 0.0.0.0 0.0.0.0 Dialer2 10

That way when ADSL is down the preferred route is via ISDN, and when ADSL is up the preferred route is via ADSL.

I have also tried adding "ppp ipcp route default" to Dialer2 and it also seems to work fine.

[tom.storey]

Ok looks like I have sorted it out by adding "dialer idle-timeout 120 inbound" to Dialer2.

Once the ADSL comes back up routing is preferred via this link over the ISDN link, so after 2 minutes of no inbound activity the ISDN drops off.

Possibly the best thing is that the ISDN doesnt drop off if it is the only link active, even if it doesnt receive any traffic for 2 minutes. Until the ADSL comes back up, the 2 minute inbound idle-timeout expires, and the 10 second disconnect delay of the dialer-wath expires, the ISDN remains up.