Skype for Business, “SIP/2.0 504 Server time-out” when trying to federate.

I recently came across a small chalenge which maybe is nothing to write about, but I choose to anyway as I came across a few solutions to this error message while I was investigating it.

The problem is the following message in the client log when trying to federate in a fresh Skype for Business on-prem environment.

Message:
SIP/2.0 504 Server time-out

ms-diagnostics: 1034;reason=”Previous hop federated peer did not report diagnostic information”;Domain=”partnerDomain.com”;PeerServer=”accessedgeFQDN.partnerDomain.com”;source=”accessedgeFQDN.yourdomain.com”

After some back and forth and checks of firewall rules and port openings, in addition to going over the topology a few times, I stumbled across the solution(which should have been pretty obvious to start with). It turned out that the SRV records for the domain had been registered with typo’s.

Solution:

Make sure you have the correct DNS entries registered in public DNS for your domain zone.
SRV records should be in the format of _sipfederationTLS._tcp.yourdomain.com weight 0 priority 0 port 5061 host accessedge.yourdomain.com.
Make sure you enter just the _sipfederationTLS._tcp part if you do this manually, as the domain name will be appended automatically in the DNS zone.

When you do a Nslookup -q=srv _sipfederationTLS._tcp.yourdomain.com, it should resolve to your access Edge FQDN in public DNS.

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Skype4B/Lync Edge Server not replicating.

In a short period of time I’ve encountered two different cases of the Edge server not replicating. Everything seems OK, but the changes simply won’t move to the Edge.

I found a great blogpost by Jaap Wesselius here that describes the exact problem and how to fix it.

Simply add the following to the registry of the Skype/Lync Edge server:

New REG_DWORD(32bit) ClientAuthenticationTrustMode with value “2” in HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\SecurityProviders\SCHANNEL

Restart the Edge server(not just the services) and toggle the Skype/Lync replication service on the FrontEnd server. Wait a few and the replication should be OK.