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Microsoft Lync not always connecting

Hi,

our MS lync 2010 was working fine. but now it seems to have for no reason started to not consistently connect.

seems internal to internal it works fine.

external to external works.

but internal to external or external to internal, it sometimes connects, sometimes not. keep getting the "call failed due to network issues"

nothing has changed on the environment. we have a MS Lync Front end and and Lync Edge in the DMZ

it was all working, but then just started coming up with this error "call failed due to network issues" when we try to connect with external users from within the network domain, and vice versa. though its intermittent.

it works, then crashes or just works fine, or it wont sign on. many times we cant connect.

do you think this is a MS lync issue or possible network issue? as if packets drop or connection not working. its very frustrating.

I have no idea what the issue is and what to do. as I have said. nothing has changed on the environment. is there any logs that need deleting? cache or anything? its a standard not enterprise to support only 80 users. not using sql db, but its own sql that installs with it.

just to provide a bit more detail

- External users can only intermittently call internal users and vice versa.  The call often fails with the message "Call failed due to network issues" - The call could not connect due to network issues.  Try logging out of Lync and logging back in, or try again later".  Eventually the call will go through if we keep trying.  
 
- We have a Lync Edge Server in DMZ and Lync Front end Server in the LAN.  Each network segment is seperated by a firewall.  We can confirm all the ports for Lync between Lync edge and Lync FE server have already been configured. We initially thought this could be an issue with a port that we have missed hence we have now opened ANY traffic between Lync edge and Lync FE server and issue still persists, we have even gone further from there by opening all traffic from a static IP of a remote user to the edge transport and issue still persists.
 
- We tried running Lync Diagnostic snooper and found no 'red' issues.
 
- Candidate information all shows proper IPs for the AV public ip.

help!

AJ
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Bembi
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OK, we move here for the moment... :-)
As you said, external / internal and vice versa is affected.

I have seen this message in earlier times which slow bandtwidt connection, so when I try to logon over a slow line. Haven't seen it in the past, but cannot definitely say it stopped by updates. But just the link to the latest LYNC updates:
http://technet.microsoft.com/en-us/lync/gg131945

Clients and server should be updated at the same time.

Another point is that I could observe connection issues, nevertheless MS stated, that UDP ports are not needed anymore. After I added them, some problems went away. Mainly for everything what is not only presence.

Third point is traffic on the external line at all or even the load on the firewall or on the edge. Especially AV produces heavy traffic. At least loading issues would be the first point i would investigate.
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ASKER

Looks like we have discovered our ISP had an issue where the fibre connection between two ISP Cisco and our Cisco. there was duplex mismatch. one half duplex and one auto sense. not sure how this changed from their end as we have no access to it.

not a network guru yet, do you think this would attribute to why internal users and external users non dependent on our edge could communicate. as I believe network connection for external is only to establish call not maintain it. or something like that.

Do you think this could be the issue. waiting for network engineers to resolve.

K*
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Bembi
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part of solution was fixing the routing issues