Recently I was assigned the task of Blocking Google Talk service for the organization I work.
In Google Talk Developer Info: it was told that the Google Talk service runs at url: talk.google.com at port 5222. Tracert revealed that talk.google.com points to talk.l.google.com @ 188.8.131.52.
But: Blocking 184.108.40.206 at port 5222 does not block Google Talk service.
Then I used WildPackets.com’s OmniPeek Personal Edition to probe out a packet level analysis.
Google Talk uses Port 80, Port 443 and Port 5223 other than Port 5222 for its communication purposes. Also: Google Talk connects to 220.127.116.11, 18.104.22.168 and 22.214.171.124 other than 126.96.36.199.
Blocking all these 4 addresses blocks Google Talk at both Browser and Talk Client. Note: This does not disable Google mail.
Bottom line: Block access to 188.8.131.52, 184.108.40.206, 220.127.116.11 and 18.104.22.168 on ports 80, 443, 5222 and 5223.
Note1: This is one of the measures to Block Google Talk. Meebo has an option wherein one can logon to any IM network., including Google, MSN and Yahoo!. So does Kool IM, eBuddy and ILoveIM. So you got to block these sites too if you want to curb IM misuse.
Note2: Geeks will get on a workaround like using an SSH Tunnel, public proxies, TOR, etc., In order to circumvent this., you got to use thirdparty traffic shapers like Akonix IM Control, Websense, etc., that sniff out Jabber traffic and prevent usage of proxies.
Note3: If you want to Block File Transfers in Google Talk block Ports 20 and 21.
Note4: This blocks Google Talk Gadget too !!!