[dns-operations] Limit on Name Servers & their IPs for a sub-domain

Paul Vixie paul at redbarn.org
Sat Jan 13 00:55:05 UTC 2018

Rubens Kuhl wrote:
>>> 11 servers. 11 labels. 11 named entities, each with a single IPv6
>>> binding..
>> In a world of IPv6 only, then can't you also safely assume an
>> end-to-end MTU of 1280 and EDNS0 support - so would 11 still be the
>> magic number?
> Only if the servers are of the *.root-servers.net
> <http://root-servers.net> format. They could be *.root-servers or *.root
> or *.rz or *.r and then a different number of them would fit into a
> given MTU, whether 512 or 1280.

turns out almost none of that matters, either for the root zone or any 
other delegation. a better reason for not adding too many server names 
or server address might be, it's more potential points of failure, and 
more points which have to be measured by the RTT-sorting many of us do.

that is, you might prefer three names, one having AAAA and A, one having 
just an A, and one having just an AAAA. anycast each A and AAAA 
independently. this is "put all your eggs into a very small number of 
baskets, and then watch those baskets very carefully."

but the reasons leading to smaller numbers don't relate to packet sizes.

and, if you really want 25 servers, packet size won't be the problem you 

P Vixie

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