Max slaves limit?

[Barry Margolin]

In article <mailman.142.1513608401.749.bind-users at lists.isc.org>,
 "Barry S. Finkel" <bsfinkel at att.net> wrote:

> On Sun, 17 Dec 2017 22:06:58 +0530, vijay bommareddy <vijayb888 at gmail.com>
> wrote:
> > Hello folks,
> > 
> > I'm trying to find more information on the practical limitations of adding
> > more slaves.
> > Can someone tell me, how many number of slaves does BIND technically
> > support? Is there a maximum limit per master server?
> > 
> > Thank you
> > Vijay
> 
> A minor point - if there are too many slaves, then the NS list might
> not fit into a UDP packet, causing TCP to be used.  I do not know
> how many NS records would be needed to exceed the UDP packet size;
> it would depend upon the length of the nodenames of the DNS servers.

That assumes all the slaves are named individually in NS records. You 
could be using anycast IPs so the same name refers to numerous different 
servers.

FYI the root zone has 13 NS records. The NS records themselves fit, but 
not all the associated A and AAAA records that go into the Additional 
section.

And if you're using DNSSEC, most responses don't fit in the traditional 
500 byte UDP packet, and EDNS0 buffer size is usually used rather than 
switching to TCP.

-- 
Barry Margolin
Arlington, MA