To find the DNS names for a specific E.164 number

Procedure is:

Write the E.164 number in its full form, including the countrycode IDDD. Example: +46-8-9761234

Remove all non-digit characters with the exception of the leading ’+’. Example: +4689761234

Remove all characters with the exception of the digits. Example: 4689761234

Put dots (".") between each digit. Example: 4.6.8.9.7.6.1.2.3.4

Reverse the order of the digits. Example: 4.3.2.1.6.7.9.8.6.4

Append the string ".e164.arpa" to the end. Example: 4.3.2.1.6.7.9.8.6.4.e164.arpa

Ask the DNS it returns:

mailto: foo@kth.se
sip: foo@kth.se

…

Transcript

[slide223] So how do we deal with the number? We take our number, we strip out all of the dashes, get rid of all the non-digits, we then put dots between them all reverse the order, and append to it e164.arpa and there we are. Why did we do the reverse? Well, because the leading digits were the country code. So this takes us from the top down through the country code through the region and eventually we get something that we can look up.