SRV, A and AAAA - SIP DNS Lookup

This SIP DNS lookup tool provides a quick method to lookup DNS records used in SIP (VoIP) from a single root domain.

SIP typically uses SRV and A DNS records (or AAAA for those IPv6 users). If you're not familiar with SRV, check out the SRV wikipedia page which is well put together. SRV is a record type designed to provide multiple servers (hostname and port) along with a priority and weight for a given service. Priority is the one to focus on first. The lower the number the more preferred the entry is. Weight is used to then decide how to route traffic between servers with the same priority. If two records with the same priority had a weight of 60 and 40, then the first would be tried 60% of the time, the second 40% of the time. Nice and straight forward.

This site works by querying the 'typical' SRV hostnames, e.g.foobar.com for SIP may have records at _sip._udp.foobar.com for SIP UDP servers, _sip._tcp.foobar.com for SIP TCP servers and maybe _sips._tcp.foobar.com for TLS as well. These SRV records then have hostname entries that need resolving again, as per normal A/AAAA records.