-----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Steve Gibbard Sent: Wednesday, April 06, 2005 8:48 PM To: Vandy Hamidi Cc: nanog@merit.edu Subject: Re: BGP Anywhere - Global Redundancy

On Wed, 6 Apr 2005, Vandy Hamidi wrote:

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Below is how I believe it should be done.

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From PDC: -Advertise CIDR block to all peers w/good metric (0 hop count) From BDC: -Advertise same CIDR block to all peers w/poor metric (+20 hop count)

To clarify, you want no traffic coming into the backup site when the primary site is up, right?

Assuming a random set of peers and upstreams, this won't actually do what I think you're trying to do. Since local-preference overrides MEDs and AS path lengths, and since you don't have control over what goes on in other networks, you'll likely get some traffic coming into your backup site even when you don't intend it to.

You could *maybe* get around this by having the same transit provider (probably just one in this case, which is scary for other reasons) in both locations. If you're paying somebody money, you have a much better chance of getting them to follow your desired routing policy. Still, it's really not good to be making a routing announcement somewhere where you don't want to receive traffic.

If you have the same ISPs at both data centers, this will work. All outsiders will route to one of your ISPs, who will send traffic to the best localpref. Until one of them loses their connection to your primary site; then it will route traffic to the backup site, even though, to you, the primary is online with the other ISPs. Convergence time across the Internet in case of complete failure could be 15 minutes, +/-5. Lee

-Steve