Multiple Default Routes

[schaef350]

I am setting up a network over two sites.  The sites are connected by a gig connections between two L3 switches.  I would like to have two default routes on the network.  Check out the diagram.

My question is what is the best way to keep both default routes on the network?  I can redistribute statics with any routing protocal but I want to favor one of the other and actually have the route go away if its connection to the internet goes away.  Can I do this all with routing protocals or do I need some IPSLA setup as well?  What would this look like as far as config goes (real generally speaking)?

[JohnTylerPearce]

My first question is what kind of connection and speed will be connecting the two sites?

[schaef350]

Variable speed internet connections, 20/5 for one and maybe a 40/40 for the other.  Like I said, a Gig pipe between the two sites then so they are connected to each other as well as any other parts of the network.

[Vineesh Viswanath]

originate defaults form boths sides , if these sites are on different l3 domain then site 1 would prefer exit via site 1 and 2 via 2 . You got to have some sort of SLA with tracking for your defaults otherwise this setup would not work on isp failure.

[schaef350]

Ok that makes sense.  Would you make each site its own routing process ID / AS or how would that look following best practices?  Not sure what protocal I will use yet... Everything is Cisco for now and I like the simplicity of EIGRP but there may be some non cisco stuff down the road ( I hope not but out of my control) so OSPF might be the ticket day 1...

Do you have a sample SLA tracking config example?  I just about have this setup and working(on lab gear).  For instance if I want to track 1.1.1.1 out site 1 and 2.2.2.2 out site 2?

[JohnTylerPearce]

If it were me, I would have each site running it's own "Routing Process". You could have SitetA (OSPF Process 1) and SiteB (OSPF Process 2). Now, depending on how you want users in SiteA to get to networks in SiteB, you could configure Policy Based Routing to say to get to networks in SiteA from B go this route instead of the default route. Of course this all depends on how you have it setup. As far as SLA tracking is considered, this will be beneficial if you have two paths to the Internet so to speak.

With IP SLA Tracking, you can track an interface and if it goes down, it goes to the next default route, which has a higher Administrative Distance. (This is a really simple way to look at it) I'll provide a link that will explain it better for you.

http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/813-cisco-router-ipsla-basic.html

[Vineesh Viswanath]

adam

on any given day i would use OSPF ... if using sla , you could track all sorts of things like an http request , echo etc ... in your case , as you are using bgp , just track 1 our more bgp routes and attach it with the default , then originate a default to your internal net based on that ... so when you lose the bgp peer , routes will disappear and your default will not get injected ...