Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp> writes:
As long as name servers with expired zone data won't serve request from outside of facebook, whether BGP routes to the name servers are announced or not is unimportant.
I am not convinced this is true. You'd normally serve some semi-static content, especially wrt stuff you need yourself to manage your network. Removing all DNS servers at the same time is never a good idea, even in the situation where you believe they are all failing. The problem is of course that you can't let the servers take the decision to withdraw from anycast if you want to prevent this catastrophe. The servers have no knowledge of the rest of the network. They only know that they've lost contact with it. So they all make the same stupid decision. But if the servers can't withdraw, then they will serve stale content if the data center loses backbone access. And with a large enough network then that is probably something which happens on a regular basis. This is a very hard problem to solve. Thanks a lot to facebook for making the detailed explanation available to the public. I'm crossing my fingers hoping they follow up with details about the solutions they come up with. The problem affects any critical anycast DNS service. And it doesn't have to be as big as facebook to be locally critical to an enterprise, ISP or whatever. Bjørn