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.

SIP/2.0 504 Server time-out

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

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.


Make sure you have the correct DNS entries registered in public DNS for your domain zone.
SRV records should be in the format of weight 0 priority 0 port 5061 host
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, it should resolve to your access Edge FQDN in public DNS.

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

  1. This is true unless you have multiple SIP domains, in which case the sipfed srv record for the non-default sip domains needs to be pointed to their own sip.domain.tld record, which then points to the access url. Otherwise you get failed federation attempts because the sip fed domain doesn’t match the domain of the access url.

  2. I’m getting this error in a hybrid setup. Where PTSN only works from on-prem accounts. Cloud homed ones don’t get any response. It worked prior to 6/8/18. Any advice in this scenario?

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