Lync Edge DNS Load Balancing call failure to PBX

Question

Hi, I have an issue with a Lync 2013 Implementation involving Edge Servers and PBX calls.
We are trying to configure 2 Edge Servers using DNS Load Balancing. We configured both servers on the topology builder, assign the correct IPs, have 6 Public IPs, 3 for each Edge. Configure NATs behind an ASA firewall, then configured the name of the edge
pool and added each Edge IP for that name on the internal DNS, also checked every port and route to make sure everything works.
All the tests related directly to Lync works, IM, Presence, Audio and Video Conferencing, Desktop Sharing, etc. However, when testing out calls from the PBX System to an Lync External client through the Edge Servers, the call rings, but never connects.
Inside the network, everything works fine, even when using only 1 Edge Server and removing the other one from the topology the call connects to the external user from the internal PBX phone. I even tried it out using one Edge first and then the other to
make sure all ports were open and everything works fine using either one, but only one at the time, not both.
The issue is only present via peer to peer call, if I first make a meet now and invite the external client, the call works.
Am I missing something with the implementation of DNS Load Balancing. 
The A Host records on the public DNS have 2 IPs for each record related to Lync Edge Services, example:
access.domain.com 200.10.10.11
200.10.10.12
audiovideo.domain.com 200.10.10.13
200.10.10.14
webconf.domain.com 200.10.10.15
200.10.10.16
Each IP is NAT'd to their respective service in its respective Edge Server. When testing I check that the DNS records are correctly responding from outside.
Any ideas on this particular issue?
Thanks once again!
Eduardo Rojas

Answer 1

Hi Edurojma,
The fact that the call rings, and then drops on answering indicates this is most likely an AV routing issue.
You advised that if you create a conference first through meet now, and then invite the participant, that the call works. But this doesn't work peer to peer.
Can I please ask that you check your static routes on your Edge server. The above sounds like the Edge has a route to your Front End server (which would be hosting the conference, hence the success), but doesn't have a route to the subnet that the client
is residing on (hence the failure).
Your Edge server needs to have routes to every subnet that is in use on your internal network.
I might be going down the wrong track, but this is quite a common problem for implementations where specific routes have been defined rather than catch all routes for every possible private subnet.
Check your edge can route to that phones subnet.
Kind regards
Ben
Blog:www.gecko-studio.co.uk/ 
Twitter:
  LinkedIn:
  Facebook:
Note: If you find a post informative, please mark it so using the arrow to the left. If it answers a question you've asked, please mark the thread as answered to aid others when they're looking for solutions to similar problems
or queries.