Lync Users from child domain are unable to communicate with Federated users

Issue: Internal users are unable to communicate with federated partners

Both parties use Open Federation. So, I have checked the UCCAPI logs after reproducing the issue.

Below is log reference

02/02/2014|20:28:56.359 D14:218 INFO  :: Data Received - *.*.*.*:5061 (To Local Address: *.*.*.*:63616) 765 bytes:

02/02/2014|20:28:56.359 D14:218 INFO  :: SIP/2.0 500 The server encountered an unexpected internal error

Proxy-Authentication-Info: Kerberos qop="auth", opaque="B65AC651", srand="38DAC634", snum="19", rspauth="040401ffffffffff0000000000000000d56cb1294aaddd51faf2098f", targetname="sip/*.domain.com", realm="SIP Communications Service", version=4

From: "TestUser"<sip:TestUser@Childdomain.com>;tag=e5eb8b9937;epid=9d9ec06d9b

To: <sip:FederatedUser@hp.com>;tag=07BCF4D13256B81D79E9A68DC93E4672

Call-ID: e8cdcc10ae654253a16910ec43813f5e

CSeq: 1 SUBSCRIBE

Via: SIP/2.0/TLS 10.160.8.134:63616;ms-received-port=63616;ms-received-cid=18C1F00

ms-diagnostics: 1008;reason="Unable to resolve DNS SRV record";domain="Child Domain.com";source="sip.domain.com"

Server: RTC/4.0

Content-Length: 0

02/02/2014|20:28:56.359 D14:218 INFO  :: End of Data Received - *.*.*.*:5061 (To Local Address: *.*.*.*:63616) 765 bytes

To resolve the issue CNAME & SRV record should be created

CNAME record to be created for Childdomain.com, Value: AccessEdgeFQDN

Federation record to be created in Public DNS

_sipfederationtls._tcp.childdomain.com 86400 IN SRV 0 0 5061 sip.childdomain.com