How many resource records can be supported by a single zone by BIND 9 ? Does anyone know if such a limit exists?

[Kevin Darcy]

Offhand, I don't believe there are any arbitrary limits. AXFRs are sent 
as a sequence of "messages" over the TCP pipe so for a huge zone it 
could just sit there and transfer all day. The only limits would be 
"soft", resource/capacity/convergence-speed limits, e.g. zone load time, 
virtual memory usage, AXFR duration, AXFR success ratio (given that 
sometimes connections drop, nameserver processes are restarted, or 
whatever), and things of that nature. Note that if the zone doesn't 
change very frequently, IXFR is going to provide one a lot more 
replication headroom than AXFR.

                                                                         
                                                                  - Kevin