Steps to replicate the issue (include links if applicable):

• Connect to irc.beta.wmflabs.org port 6667 in any IRC client, or simply via telnet as a basic health check.

What happens?:

Connection times out.

$ telnet irc.beta.wmflabs.org 6667
Trying 172.16.6.8...

What should have happened instead?:

$ telnet irc.wikimedia.org 6667
Trying 2620:0:861:3:208:80:154:72...
Connected to irc1003.wikimedia.org.

Other information:

I was looking at this subdomain because I noticed it in DNS on Horizon as part of T289318: Move *.beta.wmflabs.org to *.beta.wmcloud.org.

What I've checked so far:

• It seems to point to the correct IP (172.16.6.8). That is the IP of deployment-ircd03.deployment-prep.eqiad1.wikimedia.cloud which is the latest IRC server in Beta, per T369919: Replace deployment-ircd02 with a Bullseye or Bookworm host. No other IRC server is listed at https://openstack-browser.toolforge.org/project/deployment-prep.
• The host seems up with no notable change in host metrics seen in Grafana after its creation. WMCS Grafana - Project dash: deployment-prep, ircd03
  
• The host appears to have the right firewall ("Security Group") in Horizon, to make its port public to the world.

Security Groups for deployment-ircd03 in Horizon:

group irc

ALLOW IPv4 6667/tcp from 0.0.0.0/0
ALLOW IPv4 to 0.0.0.0/0
ALLOW IPv6 to ::/0
ALLOW IPv6 9390/udp from 2a02:ec80:a000::/56
ALLOW IPv4 9390/udp from 172.16.0.0/17

• MediaWiki RCFeed is correctly configured to send events here: Codesearch: Services irc, wgRCFeed. Noting that irc.svc points to 172.16.6.8 in Horizon under this zone (since T369919).

		'irc' => [ 'irc.svc.deployment-prep.eqiad1.wikimedia.cloud' ],
…

'wmgRC2UDPPort' => [
	'default' => 9390,
],
…
foreach ( $wmgLocalServices['irc'] as $i => $address ) {
		$wgRCFeeds["irc$i"] = [
			'formatter' => 'IRCColourfulRCFeedFormatter',
			'uri' => "udp://$address:$wmgRC2UDPPort/$wmgRC2UDPPrefix",
			'add_interwiki_prefix' => false,

• I can connect to the host, with ssh deployment-ircd03.deployment-prep.eqiad1.wikimedia.cloud
• When I run tcpdump there, and then make an edit or visit a to-me new wiki, I see messages being received from MediaWiki to the IRC server:

krinkle@deployment-ircd03:~$ sudo tcpdump -X dst port 9390

01:51:57.356469 IP deployment-mediawiki14.deployment-prep.eqiad1.wikimedia.cloud.43860 > deployment-ircd03.deployment-prep.eqiad1.wikimedia.cloud.9390: UDP, length 154
     … #central [[User:Krinkle]]@crhwiki https://crh.wikipedia.beta.wmflabs.org/wiki/Qullan%C4%B1c%C4%B1:Krinkle Krinkle *