I see lots of threads on this subject but no answers...I have something to add that maybe someone might see and it trigger an answer.
Windows 7 SP1 clients with OCS client of 3.5.6907.0 thru 3.5.6907.236....if on internal network....sign on to OCS client works fine.
When attaching to our Contivity VPN switch and gaining access to our internal network...clients had issue with OCS signing in....would not connect....OCS client could not connect to server....message was "server is unavailable"
I played around with different versions of our VPN client and OCS client....changed the OCS client to not login automatically when Windows starts...let device sit a minute or so on network after attaching to VPN...then double clicked OCS client and on the same device that would fail before...I could get the OCS client to sign in and show contact presence correctly, send and receive IMs, etc, etc...worked fine...so I thought it was a combination of newer VPN client and OCS client upgrade....and maybe DNS "jelling" on VPN enough for the OCS client to resolve the service records it needs....I don't know.
Same device that worked over VPN one day....would not work the next. Interesting part here...when I checked our Nortel 5520 Layer 2 switches....which the VPN clients go through after connection to VPN switch I noticed the MAC address in the arp table was not that of the OCS server...if I put static entry for OCS server in VPN client arp table....OCS client works fine. Problem is I don't think I can put a static entry on the Nortel 5520 switch for OCS server MAC address.
On one device...I could sign in to OCS client but no presence available....after about ten minutes on VPN all my contacts presence came in fine....I'm totally confused as to what the client is doin behind the scence.
Do I have an issue with my DNS...am I using Verizon's DNS instead of internal DNS? Most of our VPN users have Verizon broadband cards. The client can resolve the service record of _sipinternal._tcp.local.mydomain.com but then can't sign in....clients can ping OCS server....but won't connect....or if it does...no presence for the contacts.
I'll have to see if the arp entry will be the fix all the clients...hope someone has some advice. Thanks.