Saturday, July 13, 2013

Static Routes with Fast Failure Detection?

I have a nice post for you folks today. I was asked by a customer to explain how we could protect against blackholing traffic in a network that was only configured with static routes. You know those pesky problems that arise when two routers are connected on opposite ends of an Ethernet Switch or wan transport gear. A failure on one side of the link leaves the link up on the other side. Fiber cuts, clumsy engineers, failed equipment all can cause a static route blackhole. So how do we protect against this type of failure? That is a very good question and the answer is by using BFD (Bidirectional forwarding detection).
I created a video to demonstrate these capabilities. It is much easier to show folks how to do this than paste of bunch of configs into a blog post. The following video is posted on YouTube. I recommend increasing the resolution to at least 480p. Enjoy.

The Configs

Router 3

[edit]
jparks@J2350-1-R3# show routing-options
static {
    route 10.0.3.4/32 {
        next-hop 10.0.2.6;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            neighbor 10.0.3.4;
            local-address 10.0.3.3;
        }
    }
}
router-id 10.0.3.3;
autonomous-system 65006;

Router 4

[edit]
jparks@J2350-2-R4# show routing-options
static {
    route 10.0.3.3/32 {
        next-hop 10.0.2.5;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            neighbor 10.0.3.3;
            local-address 10.0.3.4;
        }
    }
}
router-id 10.0.3.4;
autonomous-system 65116;

Summary

If you need a way to prevent static routes from blackholing traffic in your network. I think BFD will be your best answer. It is configurable to detect failure in milliseconds and can be applied on just about any protocol used in the network. I have demonstrated a specific use of BFD for a simple failure scenario. What uses can you come up with?

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