[jssjr]

Sure. Feel free to call it anycast then. I usually hear anycast routing used in the context of achieving failover or routing flows to the closest server/POP, but there is probably a more formal definition in an RFC that I'll be pointed to shortly. =)

We are using BGP to advertise prefixes for GLB inside the data center to route flows to the directors. In our case all of the nodes are not on the same subnet (or at least not guaranteed to be) which is one of the reasons why we chose to avoid solutions requiring multicast. I expect Joe and Theo will get into more details about that in a future post though.

[bogomipz]

Are you running Quagga or Bird on the director instances then? I'm looking forward to reading more about it.

[logicalstack]

We use Quagga.

[jerkstate]

This is really cool work, I worked with a team that implemented an ECMP hashing scheme using a set of IPs kept alive by VRRP in a previous lifetime, so I have a bit of familiarity with the space and a few questions.

The article says the L4 layer uses ECMP with consistent/rendezvous hashing. is this vendor implemented or implemented by you using openflow or something similar? How does graceful removal at the director layer work? I know you would have to start directing incoming SYNs to another group, but how do you differentiate non-SYN packets that started on the draining group vs. ones that started on the new group?

If you are using L4 fields in the hash, how do you handle ICMP? This approach could break PMTU discovery because a icmp fragmentation needed packet sent in response to a message sent to one of your DSR boxes might hash to a different box, unless considerations have been made.