When you setup the topology for your Lync deployment you need to setup 3 simple URL’s. These URLs are used for administration, dial-in and Meet
The administration URL you keep within your internal network but the Meet and dial-in are required internally and externally. By default these are set to dialin.domain.com and meet.domain.com.
This may not seem to be a problem however if you have multiple SIP domains the number of SAN’s you require can become quite costly. A simple solution to these simple URL’s is to change them to use the same sub-domain for example lync.domain.com/dialin and lync.domain.com/meet.
Using this format halves the number of SAN’s required at the expense of slightly lengthening the actual URL.
The other consideration is that these URL’s expect you to have split brain DNS as there is no external/internal option for defining these. However if you don’t have split brain DNS the request can route externally and the meeting GRUU that is returned enables you to connect either directly internally or externally.