notify-source config with non-local IP address silently omits sending NOTIFY messages

Summary

Non-local notify-source IP address results in non-working configuration (which is kind of okay), but the problem is that there is no indication in logs that the address is incorrect.

BIND version used

• Affects v9.19: 45893249
• Affects v9.18: v9.18.11
• Affects v9.16: v9.16.39
• Other versions were not tested

Steps to reproduce

• Configure at least one zone which generates notifications
• Configure non-local IP address

Example:

zone "example.com" {
	type master;
	file "example.com.zone";
	also-notify {
		192.0.2.10;
	};
	notify-source 192.0.2.1;
	notify explicit;
};

• named.nonlocal.conf
• example.com.zone

What is the current bug behavior?

• No notifies are sent (which is probably okay by itself)
• No log message about non-existing source IP address / failed bind() call

What is the expected correct behavior?

• At least one log message

Relevant logs and/or screenshots

Apparently we do try to bind() and it fails as expected:

[pid 469186] bind(512, {sa_family=AF_INET, sin_port=htons(10053), sin_addr=inet_addr("192.0.2.1")}, 16) = -1 EADDRNOTAVAIL (Cannot assign requested address)

but it is not logged.