Dual WAN Router with Dual ISP Using BGP and OSPF

There are a small variety of methods to implement failover of your WAN perimeter between two ISPs. In this post we’ll look at one way to accomplish this goal with a few technical requirements.

Keep in mind that there are several ways to accomplish this same goal depending on the hardware available, the flexibility of the ISPs, and the skill level or preference of the engineer.

This topology utilizes two edge routers and two ISPs instead of the single edge router design I wrote about recently (you can read that here). For this post we’re using Cisco routers, but the concepts apply universally. Our requirements are that we maintain connectivity from our inside host to the internet in the event one of the company routers fails or one of the ISPs fails. Failover and fail-back must be automatic with no manual intervention.

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BGP Default Route Failover Using Reachability

Sometimes political, financial, or logistical hurdles determine how we solve networking problems. In these tricky situations we may not be able to solve the problem the way we’d prefer, but we still need to solve the problem.

In this post I’m going to look at how we can solve a WAN failover scenario¬†when we have a default route learned from both of our service providers and a reachability problem via our primary ISP.

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Fate Sharing in the Network Core

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Network engineers like redundancy. It’s not that we just want double of everything – we want the networks we design and manage to be super fast, super smart, and super resilient. In the LAN and in the data center we’ve been logically joining network switches using technologies such as Cisco StackWise, the Virtual Switching System and Virtual Port Channels with fabric extenders in order to consolidate control and data plane activities and provide greater fault tolerance, easier management and multichassis etherchannel for path redundancy. These are great benefits, but they can be reaped only by proper design. Otherwise, an engineer may introduce more risk into the network rather than make it more resilient.

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Why Buy One When You Can Buy Two For Twice the Price

I get pretty excited when new network gear shows up at the loading dock. I get psyched when I get to configure an interesting technology that I rarely get to use. But considering our responsibility to our customer or employer, sometimes we need to put that aside in favor of the simpler (or cheaper) but more appropriate solution. Let me give you one example.

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