weird network/DNS issues (nsd not returning answer)

[Aleksandr Miroslav]

On Tue, Mar 20, 2018 at 4:11 PM, Aleksandr Miroslav
<alexmiroslav at gmail.com> wrote:
> All my other servers can query k and z just fine. Only b is exhibiting
> this problem.

To be sure it wasn't an issue specific to nsd, I turned off nsd on k,
and started unbound. Other servers were able to make queries to k just
fine, but similar to nsd, queries from b came to the server and seemed
to be returned, but the return reply never got to b.

I did the same thing with a simple DNS server I found in ports,
sheerdns, same issue. Other servers were able to make queries to port
53 on k, but from b, the replies never reach the server.