ADSL with ISDN backup

When you pull out ADSL cable is your dialer goes down in a couple of minutes? I tried this on 851W router and dialer goes down in a few minutes... If this period matches the period that you see under 'idle timer' variable in the 'show dialer' output, then try to reduce this value to something more comfortable to you...

B.R. Igor

I tried that - I had it set at 10 seconds for testing but the dialer was staying up, could this be because the default route was still in the routing table and inbound traffic was still being sent that way so the router doensnt think the dialer is idle? From the info I found on setting this up I got the impression that when the backup ISDN interface comes up the ATM should go down and take the dialer with it, is it possible to force this?.

hm...strange thing... I never used before ATM interface for connecting to ADSL. I usually use PPPoE client on my Cisco routers and after provider disconnects those every 24h, dialer also comes down and up (it bounds to the virtual-profile actually).

Can I see how you defined your default route?

Also, I have another option for you: PBR with tracking option (it may not apply to your topology)

This will send IP SLA probes (icmp echo requests) to some Internet host that you define in it. When IP SLA probe fails (you don't get ICMP echo reply), your router will use next route-map 'set ip next-hop' statement (you will define it to use) to send packets to the Internet. Unfortunately, this only works if you are able to specifie next-hop ip address. I'm afraid that in your case you have to specifie one of your dialer interfaces:( ...

But send me your default route first...

B.R. Igor

Hi, thanks for your help, here are the highlights of the config, including the default route - I dont have a next hop address or routing protocol so it looks like the only option I have is the backup interface command Cheers Guy

clock timezone . 0 clock summer-time BST recurring last Sun Mar 1:00 last Sun Oct 2:00 mmi polling-interval 60 no mmi auto-configure no mmi pvc mmi snmp-timeout 180 ip subnet-zero ! ip name-server 62.241.162.200 isdn switch-type basic-net3 ! interface FastEthernet0/1 ip address *.*.*.* 255.255.255.248 duplex auto speed auto ! interface ATM0/0/0 no ip address backup interface BRI0/1/0 no atm ilmi-keepalive dsl operating-mode auto pvc 0/38 encapsulation aal5mux ppp dialer dialer pool-member 2 ! ! interface BRI0/1/0 no ip address encapsulation ppp dialer pool-member 1 isdn switch-type basic-net3 no keepalive ! interface Dialer0 ip address negotiated encapsulation ppp dialer pool 1 dialer string 08450795056 dialer-group 1 ppp chap hostname * ppp chap password * ! interface Dialer2 ip address negotiated encapsulation ppp dialer pool 2 dialer idle-timeout 10 dialer-group 2 no cdp enable ppp chap hostname * ppp chap password * ! ip classless ip route 0.0.0.0 0.0.0.0 Dialer2 ip route 0.0.0.0 0.0.0.0 Dialer0 80

Try with this:

interface Dialer2 no dialer-group 2

This should eliminate interesting traffic issue, that is, maybe there is always some interesting traffic that keeps this dialer up...

B.R. Igor

Thanks again, I will give that a go - I cant try it until wednesday evening though, I will let you know how it goes

Cheers Guy

You need to take a different approach to failover. Backup interface requires the interface being backed up to fail but dialer interfaces never go down, they are either UP (for real) or UP (spoofing).

You need to design your backup scheme using a mechanism which does not depend on the dialer going down. Normally, this is done through a routing protocol, but that is rarely an option with ADSL ISPs. Most people in your situation use "ping based routing" to detect loss of the ADSL link (a fringe benefit of Cisco's Response Time Recorder feature) and use that to activate/deactivate the default route through the ADSL link. A floating static route can then be used to activate the ISDN backup. But be aware that this approach has some nasty side effects if you are performing NAT on both ADSL and ISDN paths inside the router. It also may require you to manually reactivate the ADSL link before its return to action can be detected.

Good luck and have fun!

Vince,

If you don't think on PBR with tracking option, can you provide some links for "ping based routing"?... I didn't know until now that this feature exists... I used before only PBR with tracking option and Cisco IP SLA monitoring.

Thanks in advance... B.R. Igor

Could you rephrase the clause leading up to the first comma? I can't parse it, which makes it hard to reply.

In Cisco IOS, "ping based routing" can be done using PBR with tracking option, so I think we're using different terms for the same features. When first introduced, Cisco called it their "Response Time Recorder" (RTR) feature.

Yes, It seems that we are using different terms for the same feature...

But I think that this won't help to Guyster's issue, because when you use 'verify-availability' route-map 'set' statement then only option, I get is to specifie next hop ip address. I'm afraid that Guyster due to the nature of his Internet connections doesn't know what the next-hop ip will be next time he connects.... On the contrary if he can predict next-hop ip then this is perfect solution for him... I don't understand why Cisco doesn't supports 'set next-hop interface' with object tracking or even possibility to redistribute routes depending of tracking object status...

B.R. Igor

Hi Guyster,

If my memory serves me right, the way to do this is to interchange your floating static. Use the dialer interface of isdn as primary and the adsl as secondary. The rest, let the backup interface do the job of making the dialer interface to be on standby. "backup int dialer #". This will make the adsl as the active route while the isdn is down.

Cheers, Jeff

Hi guys, I have just found out that the ISP at this site don't support this kind of setup - they have public IP addresses inside the router and the ISP route all the traffic to this subnet via the IP address that is assigned to the ADSL interface, so it wont work anyway!! The guys at the site are looking for service that will deliver on their requirements. I take it with the PBR option you are only using ping to check the availability of the ADSL otherwise it would rack up the bill on the ISDN line!

Cheers Guy