Frame Relay Internet with ISDN Internet Backup

Hi,

I preface this post with "I know similar posts have been made over the
years, but I can't for the life of me find a close enough match to
solve my problem" so that I don't end up with too many flames.

I have a cisco 2621XM (2 ethernet ports), with a WIC2T serial card
(two serial ports), and a BRI card, running IOS 12.3

The main link to the internet is frame relay through a serial
interface, single DLCI for internet. The serial interface is
numbered.

We have a secondary ISDN link (doing nothing currently) through
another ISP (so different IP address range, dns servers etc).

What I'd like to do is have the router detect when the frame link is
down, and automatically switch to the isdn. I've heard Dialer Watch
is the way to go for this.

I realise there would be some serious issues to be dealt with in
regards to:

- ethernet interface ip address
- routing traffic/default route (0.0.0.0)
- dns servers

I have looked at relevant technotes and newsgroup postings, but in
each instance it has normally related to the creation of a backup
mechanism for point to point communication (eg building to building,
rather than internet sources), rather than trying to utilise a
different source for internet access.

I'm not sure how to progress with this, I need some solid guidance
(and small examples!) of what I need to do, if this is even possible.

Any help is appreciated. Post/Email is fine.

Greg Krzeszkowski

 

Hm....I had the same issue with one of my customer and eventually advise
them to get a 800 series ISDN router. But I have thought of the same
implementation :

1) Ethernet Interface - try using secondary IP address on the Ethernet
Interface
2) default route- use floating static route
3) DNS server - Are you hosting one with the public ip address given by the
FR ISP?