3640 Auto-Failover to Back-Up CKT

[StarTAC]

hi guys...

i have a satellite link with 2.5Mbps, which is my primary internet circuit... however, i have an HDLC leased line circuit connected to the same 3640 router, which routes back to a government satellite antenna, for backup, in case my primary link goes down....

i would like your help on two issues:

o how the router can auto switch to the backup link once the primary link has failed...

o how i ensure that all clients maintain their IP addresses but still uplink through the backup link....

all help appreciated... thanks..

 

[svermill]

Are both satellite shots up at all time? From a simple routing perspective, you can just add default route pointing towards your backup link with a manually assigned administrative distance that is higher than what is being advertised for your primary connection. It won't kick in until the lower AD route disappears. That is probably an over-simplification for your exact application, but that's the concept anyway. If both shots aren't up, dial on demand routing has worked well for me on many occasions. The "floating static route" still applies.

When you talk about a "government" antenna, you introduce some sticky issues. Where does that antenna point to? Somewhere that can and will advertise your address space so that return traffic from the Internet can find its way back to you? If not (and I doubt it), you will be borrowing address space from your government folks. NAT could solve some of your problems for local users browsing around. However, if you had a web server or something that you want outside people to be able to reach via your backup link, you've still got some potentially nasty issues.

 

[RickM512]

I'd have to dig up some old configurations but I did somewhat the same thing but with ISDN as a backup using Floating static routes with a metrix of 150.

 

[StarTAC]

my current CKT has a DVB downlink.. if i had an issue, it would always be with the uplink.. the DVB stays alive, and that would be the return path for the traffic... we would only need the government satellite for uplink.. our downlink would still work after a failure....

however, both links are basic HDLC links, without any intelligent routing... how would i be able to use metrics for the link to know when the other is down, or up..?..

all help appreciated...

 

[svermill]

Sorry for the delay. I didn't see you latest post until today. I'm not sure how exactly to help you. Manipulating administrative distance is a useful tool but requires that the router become aware of any failure of the primary link before it will enter the backup into the routing table. Without a failure of the downlink, I'm not sure how the router would ever know when to intervene. Are your downlink and your uplink on totally different interfaces? Is it possible that whatever you uplink interface is tied to would drop a control lead, such as carrier detect, if the uplink is lost? If so, there are options.

 

[routerhead]

You may want to use backup interface or watch lists, which are much better than floating static routes. They do not pass routing table information when primary goes down....

 

[svermill]

Dialer watch might be an intereting avenue to pursue. The problem for RickM512 is that he is only going to loose his uplink - not his downlink. And I think he mentioned that there is no routing protocol running between him and the other side of that satellite link. Dialer watch is tied to a routing protocol such as RIP or EIGRP.