Url need to be open for definition update in SEP

I usually just use the ping command between servers and clients and even to the Symantec servers. Sometimes use netstat and a different application to check for open ports.

But there is a whitepaper on best practices that you may want to look over:
http://service1.symantec.com/support/ent-security.nsf/854fa02b4f5013678825731a007d06af/d29b17f62f36c49f882573b400333bd4?OpenDocument

Hi Sam, we use telnet just to test the connection or to verify if the ports are open.

Telnet (teletype network) is a network protocol used on the Internet or local area networks to provide a bidirectional interactive communications facility

its just a tool , in some companies they disable telnet too , does not mean that they dont get symantec liveupdate.

we use telnet to test the connectivity, whether its able to reach the destination on the port 80,

telnet ip port ( format) 

This document would help you to know whats needed for symantec liveupdate

How to determine whether your firewall is blocking LiveUpdate

http://service1.symantec.com/SUPPORT/sharedtech.nsf/d3c44a1678bd8f45852566aa005902cb/c0aeb869920b38b688256d980074e389?OpenDocument&prod=Symantec%20AntiVirus%20Corporate%20Edition&ver=10.0&src=ent&pcode=sav_ce&dtype=corp&svy=&prev=&miniver=sav_ce_10

the site you mentioned above is the right site where the symantec gets the update all you have to do is to open the port just to successfully download the updates