HSRP with ISDN as secondary link

[jimmyjoseph]

Hi,

I have a branch site connected to my main office using a 128 Kbps FR link. The FR link is terminated on a 2621 router at the branch and on a 3640 at the central office. Now i need to avoid single point of failures for both hardware and connectivity . My idea is to implement standby routers at both ends using HSRP and ISDN as redundancy for FR.

Is this a good design? When the FR interface on router-A at the central office goes down , the ISDN on router-B would initiate a call to router-B at remote office and establish connection . This is my logical thinking. Is there a better way fo doing this? What are the things which i should keep in mind while going ahead with this?

All suggestions are welcome.

regards,

jimmy.

[Georg Pauwen]

Hi Jimmy,

I have a customer with a similar setup, primary line is a 2MB SDSL, backup is a PRI, and HSRP configured between the routers. As far as I can tell it works just fine.

Regards,

Georg

[jimmyjoseph]

Hi Georg,

When the Primary 2 MB link goes down how does the ISDN dialer interface on the second router get a trigger to initiate dialing. As far as i understand , when the primary circuit goes down HSRP has to inform secondary router to become active and also initiate the dialing of ISDN. Could you throw some light on how you have accomplished this. I am not very experienced with ISDN DDR configuration and setup

regards,

jimmy.

[Georg Pauwen]

Hello Jimmy,

I don´t know the entire config off the top of my head, I will have a look tomorrow and send it to you.

Regards,

Georg

[jimmyjoseph]

Georg,

Sounds great. Appreciate your help.

regards,

jimmy.

[benjamingarcia]

HSRP is a very straigth forward. See the attached shortcut, you will need a CCO login. Learn the use of prempt and interface tracking

To answer your question on how the ISDn will be trigger. HSRP send a packet every # of second between routers to find out its status. The debug output will reveal the secret.

http://www.cisco.com/cgi-bin/Support/browse/psp_view.pl?p=Internetworking:HSRP

[hvd]

Hey Jimmy, Georg

I just got a similar project over here.

We've got one router connected at 64K serial line.

A second router needs to be installed in HSRP config, and when the primary 64k goes down this second router needs to dial out via ISDN.

Would appreciate if you could send me that config too, I hope it's not using BGP, I'm a bit in the dark too.

Thx Hans

[vcjones]

I've been doing this since circa IOS 11.0! There are several example configurations in my book High Availability Networking with Cisco (listings are on my web site). See Chapter 5 "Multiple Routers at a Single Site" which has a section on "Dial Backup by One Router for a Line on Another." You can do it with dialer watch (use IOS 12.1(5) or later only) or with BGP (any IOS with DDR and BGP support). Note that since I wrote the book, Cisco has fixed dialer watch to work with all routing protocols, so ignore that comment in the book.

HSRP should be configured independently of the dial backup, because the dialer link never goes down (so you can't track it) and the serial line may not go down at the link level (particularly if frame relay) even though all traffic has been forced over to the backup path. Configure a dynamic routing protocol (EIGRP or OSPF) between the routers so that all routers can find the working path, regardless of the mode of failure. That way, while HSRP will protect you from router failure and may eliminate extra hops during link failure conditions, you are not dependent on it working under all conditions for your backup plan to work. (been there, done that, been burnt...)

Good luck and have fun!

Vincent C Jones

http://www.networkingunlimited.com