What happens when one router down if switch has 2 default routing to 2 routers?

[getaway51]

I have core switch with 2 default routing.

0.0.0.0 0.0.0.0 1.1.1.1

0.0.0.0 0.0.0.0 1.1.1.2

1.1.1.1 & 1.1.1.2 are router 1 & 2 HSRP IP.

What happens if 1.1.1.2 is down?

1)Will core switch still sending packets to 1.1.1.2?

2)Does it means that traffic will lost?

3)Does it means that all routing must be accompanied by SLA to make sure no traffic lost?

[Francesco Molino · Accepted solution]

Hi

First of all if your 2 routers are in hsrp, then no need to have 2 static default route.

Your static default route should have the vip of your hsrp as next-hop. 

This vip is defined on your router with the command standby ip x.x.x.x

Next regarding your questions.

When 1.1.1.2 goes down, if your exit interface on your core switch is up, the route stays in your routing table which means traffic going toward it will be lost (blackhole). 

For the router to clean this route from the routing take, the exit interface to reach the next hop has to be go down.

Also, if your default routes have same AD, then traffic will be load balanced to router 1 and 2.

Which means not all traffic will be lost but only the one forwarded to this unreachable next hop.

To force removing a route from your router RIB, you need to do a tracking (using ip sla) and if this tracking changes to status down, your route will be removed. If it goes up, the route goes back into your RIB. But again, if your routers are in hsrp, just set 1 route with hsrp ip and no more issues.