DNS pulling BGP routes?

Wed Oct 6 19:32:10 UTC 2021

----- On Oct 6, 2021, at 10:42 AM, Michael Thomas mike at mtcc.com wrote:

Hi,

> My guess is that their post while more clear that most doesn't go into
> enough detail, but is it me or does it seem like this is a really weird
> thing to do?

In large environments, it's not uncommon to have DNS servers announce
themselves on an anycast IP. This is also referred to as "host BGP". 
Basically, the host (or hypervisor) speaks BGP with the TOR. Your spines
or superspines will then pick a best route or ECMP across multiple DNS
servers. 

My guess is that Facebook took this concept a step further and anycasted
their public DNS servers through their datacenters to the internet. One
single config change made the DNS servers think that they were no longer
functioning properly which caused them to withdraw the routes. At least,
that's what I understand from the post-mortem.

Thanks,

Sabri