One Cisco router, two ISPs - gateway redundancy?

June 18, 2009 7:29 AM

One Cisco router, two ISPs - gateway redundancy?

I'm looking for a way to use two ISP connections (one cable, one DSL) to provide gateway redundancy. What I mean is, if one gateway stops working for any reason, I would like to router to start using the other gateway automatically. Is it possible with one router, and how would it be done?

What I'd like to do is connect the equipment from the ISPs to a switch and connect the WAN of my Cisco router to the switch as well. Then I would assign the static IP address from each ISP to a separate virtual interface each on the WAN of the Cisco.

Does this make any sense? Would I need two routers to do it? Or would i need two physical interfaces?

posted by doomtop to computers & internet (10 comments total)

BGP
posted by b1tr0t at 7:42 AM on June 18

I don't think BGP is going to be an option. I would rather do something strictly on the local network.
posted by doomtop at 7:49 AM on June 18

Good grief, do NOT do BGP. It's overkill in the highest form.

Look at "ip sla" tracking.

Two things to bear in mind -- outbound sessions will need to reconnect if you switch gateways (you'll NAT to a different external address). If you have a significant number of inbound connections you'll need to be careful with your failover scenarios to make sure it works....
posted by devbrain at 7:53 AM on June 18 [1 favorite has favorites]

Inbound connections are not really a concern right now. There are some, but they aren't used enough to where it would be a problem when the switchover happened. If I could get it to switch back to the "main" gateway when it came back up, I would be back on the main IP address and it wouldn't be a problem anymore. So the only issue would be inbound connections while the "main" gateway was down and that would be a problem anyways. With the switchover to a secondary gateway, users on the LAN would still be able to get to the Internet, even though they would have to re-establish their session, as you say. That is acceptable.
posted by doomtop at 8:08 AM on June 18

Also, devbrain, I just looked into ip sla tracking, and this looks like exactly what I was looking for. Thanks!
posted by doomtop at 8:10 AM on June 18

ahh too late to the party, ip sla is the right way to do it at home, nobody will do BGP or give you space large and portable enough unless you're doing ipv6.
posted by iamabot at 8:44 AM on June 18

I'm really behind on my knowledge. I was going to say, "Why not just throw a floating static route on there?" But IP sla is like the floating static route...with help. I know, I'm too late to really answer the question, but I'm glad I saw it.


And...no sarcasm at all - does anyone really use bgp at home?
posted by routergirl at 9:26 AM on June 18

Two example configs I've bookmarked on Cisco's site for doing something like this. I can't vouch for them. My config was sufficiently different from either one that getting it to work was taking more time than it was worth to me.
posted by Good Brain at 10:56 AM on June 18

Was curious and googled this a bit, and found this:

Multihomed failover appliance

I know nothing about it, but thought I would pass it on in case it was useful.
posted by Antidisestablishmentarianist at 11:11 AM on June 18

And...no sarcasm at all - does anyone really use bgp at home?

Yes, but probably not many. Those who do are the nerd equivalent of bodybuilders. They want to show of their incredible nerdness with excessive use of routing force.

If it were me, I'd unplug my linksys router from the dead connection and plug it in to the live connection. Or maybe power on my Kindle. Or go for a walk.
posted by b1tr0t at 7:00 PM on June 18