John Lange said:
"1) Device determines its IP address by querying the STUN server
2) Device determines its domain name using reverse DNS.
3) Device does LIS discovery via DNS (SRV/NAPTR)."
There are some situations in which steps 1 and 2 will not work reliably.
With IPv4 exhaustion looming, it is likely that service providers will implement some form of IPv4 address sharing.
In an access network that has deployed a Carrier Grade NAT (CGN), step 1 will produce an IP address on the CGN,
not the outer address of the residential CPE. This could then result in discovery of a LIS on the wrong side
of the CGN, which would find itself unable to provide location since the source IP address will have been shared
by too many users.
An alternative approach to obtaining a suitable domain for step 3 would be to use the Domain Name Option (RFC 2132)
which is commonly supported today. The Searchlist Option (RFC 3397) is another possibility but it is not as
widely supported. This could produce a suitable domain without requiring the implementation of STUN or population
of PTR RRs.
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