This related to a Steam ban possibly? Open Steam and goto settings... under the Account tab - first one there that opens... it says 'VAC status' which normally reads: "In good standing" or will read "Banned from some secure servers due to a cheating infraction" or another message... check to see if that person has been banned... you can also do this by checking their profile and the box on the right with stats/friends etc. statuses... it should say "Member Since:" "Steam Rating" and have your "Playtime" stats for recently played games -- where it says that for those that are banned, it appears in red bold lettering and says "Ban(s) on record"...
I do understand this may not apply to you as you've said you can connect every once in awhile... but this may be the case for those you said cannot connect at all no matter what they do, and maybe not... do all of you have ports forwarded correctly? From:
http://www.nwo.dk/index.php?option=com_kunena&func=view&catid=4&id=3591&Itemid=8 6
The first post there states:
According to Activison the following ports should be forwarded:
UDP: 27000-27015, 27015-27030, 3074
TCP: 27014-27050, 3074
I also have a few more, 1500, 3005, 3101, and 28960 that are forwarded for MW3, and as far as the 27xxx and 28960, you won't need either unless you are hosting a dedicated server, but possibly there is conflict with the router/firewall blocking these ports as you attempt to login/play, therefore forwarding may help somewhat, but you can also confirm with software based firewall and antivirus to make sure thats not conflicting either.
Ah, a better post of that:
Mw3 -
UDP: 27000-27015, 27015-27030, 3074
TCP: 27014-27050, 3074
UDP 1500 (outbound only, no forward needed)
UDP 3005 (outbound only, no forward needed)
UDP 3101 (outbound only, no forward needed)
UDP 28960 (inbound/outbound, must forward to act as a multi-player host, but no forward or inbound traffic needed to find and join games)
UDP 1500 (outbound)
UDP 3005 (outbound)
UDP 3101 (outbound)
UDP 28960
Steam Client -
UDP 27000 to 27015 inclusive (Game client traffic)
UDP 27015 to 27030 inclusive (Typically Matchmaking and HLTV)
TCP 27014 to 27050 inclusive (Steam downloads)
UDP 4380
enable dmz and enable UPnP
**NOTE: You DO NOT and probably SHOULD NOT enable DMZ, usually UPnP is standard ON with most router configurations.**
DMZ basically overrides everything set and allows anyone access at your machine, USE AT YOUR OWN RISK.
