DNS pulling BGP routes?

Sat Oct 9 08:37:09 UTC 2021

Christopher Morrow wrote:

>> means their DNS servers were serving the zone, even after they
>> recognize their zone data were too old, that is, expired.

> that's not what this means. I think Mr. Petach previously described
> this,

He wrote:

> So, the idea is that if the edge CDN node loses connectivity to
> the core datacenters, the DNS servers should stop answering
> queries for A records with the local CDN node's address, and
> let a different site respond back to the client's DNS request.

which may be performed by standard DNS with short expire period,
after which name servers will return SERVFAIL and other name
servers in other edge node with different IP addresses are tried.

It may be that facebook uses all the four name server IP addresses
in each edge node. But, it effectively kills essential redundancy
of DNS to have two or more name servers (at separate locations)
and the natural consequence is, as you can see, mass disaster.

> but: 1) dns server in pop serves some content (ttls aren't
> important right now)

You MUST distinguish TTL and EXPIRE. They are different.

 > there's not a lot of magic here... and it's not about the zone data
 > really at all.

Statement of Petach: "the edge CDN node loses connectivity to
the core datacenters, the DNS servers should stop answering"
means, with DNS terminology, zone data is expired, which has
nothing to do with TTL.

						Masataka Ohta