bind 9 forwarders: use UDP or TCP?

UNIX for Advanced & Expert Users
1

I use forwarders for a subzone, but TCP 53 is blocked, So does forwarders really need TCP?
If forwaders use UDP, I can't get following scenario to work:
main zone is master, but subzone is forwad. Is it possible?
(On name sever itself, resolution of xx.stub.abc.com worked fine.)

 
#sub zone
zone "stub.abc.com" {
 type forward;
 forward only;
 forwarders { 1.1.1.1; };
};
 
#main zone
zone "abc.com" {
 type master;
 ...
};
2

As far as I know you need to have port 53 open for both UDP and TCP.

Most normal DNS traffic uses UDP not TCP. However AXFR uses TCP
to replicate zone data.

3

yes, TCP 53 is needed for zone transfer "slave type", but I couldn't find any info about protocol used for r" forward type"

---------- Post updated at 02:50 PM ---------- Previous update was at 10:53 AM ----------

I think sub-zone using forwaders is not going to work.
I ended up using sub-zone delegation, which use UDP only.

CTX124727 - How to Configure DNS Delegation Using BIND - Citrix Knowledge Center