BIND Slave Receiving Notify From Other Slave?

Question

I have a master nameserver setup with a few slaves as well. Today I was changing one of the slaves to a new server when I came accross a weird error message.
After updating the DNS records on the master and restarting BIND, I noticed that ns3.mydomain.com was trying to send ns4.mydomain.com a notify. I've checked the configuration files and no where does it have the IP address for ns4.mydomain.com in the ns3.mydomain.com configuration files.
Shouldn't it be ns1.mydomain.com sending the notify to ns4 and not ns3? I should also note that the DNS records on both ns3 and ns4 seem to be updated.

Here's the error messages on ns3 (IP Address: 107.161.xxx.xxx):

May 15 22:08:22 vps named[23851]: client 185.38.xxx.xxx#59396: received notify for zone 'mydomain1.com'
May 15 22:08:22 vps named[23851]: zone mydomain1.com/IN: refused notify from non-master: 185.38.xxx.xxx#59396
May 15 22:08:22 vps named[23851]: client 185.38.xxx.xxx#59396: received notify for zone 'mydomain2.com'
May 15 22:08:22 vps named[23851]: zone mydomain2.com/IN: refused notify from non-master: 185.38.xxx.xxx#59396
May 15 22:08:22 vps named[23851]: client 185.38.xxx.xxx#59396: received notify for zone 'mydomain3.com'
May 15 22:08:22 vps named[23851]: zone mydomain3.com/IN: refused notify from non-master: 185.38.xxx.xxx#59396
May 15 22:08:23 vps named[23851]: client 185.38.xxx.xxx#59396: received notify for zone 'mydomain4.com'
May 15 22:08:23 vps named[23851]: zone mydomain4.com/IN: refused notify from non-master: 185.38.xxx.xxx#59396

Here's the error messages on ns4 (IP Address: 185.38.xxx.xxx):

May 15 22:08:22 uk named[572]: client 107.161.xxx.xxx#48742: received notify for zone 'mydomain1.com'
May 15 22:08:22 uk named[572]: zone mydomain1.com/IN: refused notify from non-master: 107.161.xxx.xxx#48742
May 15 22:08:22 uk named[572]: client 107.161.xxx.xxx#48742: received notify for zone 'mydomain2.com'
May 15 22:08:22 uk named[572]: zone mydomain2.com/IN: refused notify from non-master: 107.161.xxx.xxx#48742
May 15 22:08:22 uk named[572]: client 107.161.xxx.xxx#48742: received notify for zone 'mydomain3.com'
May 15 22:08:22 uk named[572]: zone mydomain3.com/IN: refused notify from non-master: 107.161.xxx.xxx#48742
May 15 22:08:22 uk named[572]: client 107.161.xxx.xxx#48742: received notify for zone 'mydomain4.com'
May 15 22:08:22 uk named[572]: zone mydomain4.com/IN: refused notify from non-master: 107.161.xxx.xxx#48742

Solution 1

Either specify notify master-only; in the options section or specify notify no; in the slave zone definitions if you do not want notify messages to be sent.

Notify messages are by default sent to all the zone's nameservers (based on NS records in zone data) except that of SOA MNAME (also see notify-to-soa).

Solution 2

I think you need to apply the allow-notify { address_list }; statement in the options of slave zone name servers, where 'address_list' should be the source IP of master name server's notify message.