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Beginner

ISDN BACKUP OF ISDN?

Hi !!!

I have one 800 series with one isdn and eth interface.How can I configure the backup option in case that one dialer can not establish connection with first provider to use other dialer and make connection over the same isdn interface.

Is it possible?

THANKS!!!!

6 REPLIES 6
Engager

Re: ISDN BACKUP OF ISDN?

Hi Fisko,

You can do that....I suppose

Just create 2 dialer interface and under first dialer interface give a command dialer pool 1 and under another dialer interface use dialer pool 2.

Now under your physical interface give 2 command

dialer pool member 1 and dialer pool member 2.

Now your physical interface will be binded to 2 dialer interfaces and it will try to call first dialer interface and if it dies not work it will call 2nd dialer interface.

Try this and update how it worked.

Regards,

Ankur

Beginner

Re: ISDN BACKUP OF ISDN?

Ok I think that is the way for the configuration.

But I am not shure about routing. On the other part of ISDN I have 2 different subnets and I dont know how to make one dialer down while other is up. In backing up of serial links I have a DDR with static floating. In this situation this is not possible.

I have 2 different locations with 2 different subnets and only one should be active.

Does one dilaler stay down if the one is up if I had static routes?

Regards

THANKS A LOT!!!!!!!

Fisko

THANKS A LOT!!!!

Engager

Re: ISDN BACKUP OF ISDN?

Hi Fisko,

Hope you are doing good!!

At a time out of 2 dialer interface only one will be binded with the physical interface.

Now configure 2 static route with different admin distance and give the exit interface as Dilaer

Eg: ip route x.x.x.x x.x.x.x Dialer 1 180

ip route x.x.x.x x.x.x.x Dialer 2 185

Now for suppose your Dialer 1 is binded with the bri interface that time Dialer 1 interface is active and it will call first static route and once Dialer 1 is not available it will try calling Dialer 2 and it will install second static route with Dialer 2 as exit interface in routing table.

Hope I am clear and this helps you.

Regards,

Ankur

Highlighted
Contributor

Re: ISDN BACKUP OF ISDN?

As you have no doubt discovered by now, backing up a dialer with another dialer is not as easy as it seems. The problem, of course, is that dialers are always up, so floating static routes are ineffective. In a controlled environment (where you control the routers at both ends), it is fairly easy to do with dialer watch and filtering of target routes (see the white paper on my web site). However, if you do not have the luxury of running a routing protocol, it gets amazingly difficult. You may be able to "ping based routing" but I am not sure how well that is supported on the 800 series. Worse, if you only want the primary link up when it is needed (dial on demand), there is no known IOS supported reliable way to achieve failover.

You're doubly hosed if the router must do a different NAT for each dialer. In that case, it is not enough to just start using the alternate dialer, you also need to clear out all the old NAT translations for the defunct dialer (hint: NAT policy maps only apply when setting up a NAT and are ignored once the NAT is in the translation table).

In the past, those with a need have addressed it using external black boxes to do the job, but be aware that ad hoc solutions have a nasty habit of only working most of the time, and failing when you can least afford the down time.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

Participant

Re: ISDN BACKUP OF ISDN?

Hi, I have this exact scenario working in production on (25) 802 routers. It really works nicely. A floating static route is configured to point to D2 which of course dials another location in the event there is an issue with where D1 is set to dial. It took me awhile to get it to work the way I wanted it, but it achieves the redundancy of an ISDN line backing itself up.

Beginner

Re: ISDN BACKUP OF ISDN?

THANKS ALL!!! I will try to make this and give a feedback about this!

THANKS A LOT!!!!

Best Regards

Fisko

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