Discussion List for Freenum/ITAD Subscriber Number (ISN) Project

As far as I can tell from reading the current RFC that governs NAPTR
records, RFC 3402 section 3.2, the substitution specified in the NAPTR
record must be applied to "the String" in a similar manner as is done
by the "sed" program, which is that the substring that is matched by
the regexp is to be replaced by the string generated by the
replacement field.  What this turns "the String" into is (in our case)
the result of the NAPTR, which is to be a URI.

The de-facto standard for ISN NAPTR records is given in the ISN Cookbook:

*.xxx.freenum.org IN NAPTR 100 10 "u" "E2U+sip" \
        
"!^\\+*([^\\*]*)!sip:\\!"
 .

The regexp is:

        ^\\+*([^\\*]*)

This matches any string with an initial sequence of "+", then any
number of non-"*" characters.  The non-"*" characters are extracted as
substring 1.

Now "the String" for ISN lookup doesn't seem to be specified anywhere,
but from the structure of this regexp, we can see that it's expected
to contain a "*", following the organization-specific extension
number, but the most reasonable hypothesis is that "the String" is the
ISN number itself, possibly with a leading "+".

But since the regexp doesn't match the whole ISN number, the
substitution operation will progress like this:

Input:
        456*123
        ^^^-------- part matched by regexp

                    substring 1 = "456"

                    replacement string = 
"sip:"

Output:
        
sip:*123

Which isn't a URI, or at least, not the one we want.

That is, the regexp needs to be changed to match the *whole* ISN
number, so that the replacement string replaces it entirely.  An
appropriate NAPTR would be:

*.xxx.freenum.org IN NAPTR 100 10 "u" "E2U+sip" \
        
"!^\\+*([^\\*]*).*$!sip:\\!"
 .

There aren't a lot of authoritative examples of NAPTR records, that I
can use to check that my interpretation is correct, but I can find
these in the RFCs:

rfc2168.txt:   IN NAPTR 100   10   ""  ""  "/urn:cid:.+@([^\.]+\.)(.*)$/\2/i" 
   .
rfc2915.txt:   IN NAPTR 100   10   ""  ""  "/urn:cid:.+@([^\.]+\.)(.*)$/\2/i" 
   .
rfc2915.txt: IN NAPTR 100 10 "u" "sip+E2U"  
"!^.*$!sip:!"
     .
rfc2915.txt: IN NAPTR 102 10 "u" "mailto+E2U" 
"!^.*$!mailto:!"
  .
rfc2916.txt:   IN NAPTR 100 10 "u" "sip+E2U"    
"!^.*$!sip:!"
     .
rfc2916.txt:   IN NAPTR 102 10 "u" "mailto+E2U" 
"!^.*$!mailto:!"
  .
rfc2916.txt:  IN NAPTR  10 10 "u" "sip+E2U"     
"!^.*$!sip:!"
    .
rfc2916.txt:  IN NAPTR 102 10 "u" "mailto+E2U"  
"!^.*$!mailto:!"
 .
rfc2916.txt:  IN NAPTR 102 10 "u" "tel+E2U"     "!^.*$!tel:+4689761234!"     .
rfc2916.txt:   * IN NAPTR 100 10 "u" "ldap+E2U" 
"!^+46(.*)$!ldap://ldap.se/cn=01!"; .
rfc2916.txt:    IN NAPTR 10 10 "u" "sip+E2U"    
"!^.*$!sip:!"
        .
rfc2916.txt:    IN NAPTR 10 10 "u" "mailto+E2U" 
"!^.*$!mailto:!"
     .
rfc2916.txt:    IN NAPTR 10 10 "u" "http+E2U"   
"!^.*$!http://svensson.ispa.se!"; .
rfc2916.txt:    IN NAPTR 10 10 "u" "tel+E2U"    "!^.*$!tel:+46-8-9761234!"    
   .
rfc2916.txt:    IN NAPTR 10 10 "u" "sip+E2U"    
"!^.*$!sip:"
        .
rfc2916.txt:    IN NAPTR 10 10 "u" "mailto+E2U" 
"!^.*$!mailto:"
     .
rfc2916.txt:    IN NAPTR 10 10 "u" "http+E2U"   
"!^.*$!http://svensson.ispa.se"; .
rfc2916.txt:    IN NAPTR 10 10 "u" "tel+E2U"    "!^.*$!tel:+46-8-9761234"     
  .
rfc3403.txt:  IN NAPTR 100   10   ""    ""  
"!^urn:cid:.+@([^\.]+\.)(.*)$!\2!i"    .
rfc3403.txt: IN NAPTR 100 10 "u" "sip+E2U"  
"!^.*$!sip:!i"
     .
rfc3403.txt: IN NAPTR 102 10 "u" "smtp+E2U" 
"!^.*$!mailto:!i"
  .
rfc3404.txt:IN NAPTR 100   10   ""    ""  "!^cid:.+@([^\.]+\.)(.*)$!\2!i"    .
rfc3761.txt:      NAPTR 10 100 "u" "E2U+sip" 
"!^.*$!sip:!"
 .
rfc3761.txt:      NAPTR 10 101 "u" "E2U+h323" 
"!^.*$!h323:!"
 .
rfc3761.txt:      NAPTR 10 102 "u" "E2U+msg" 
"!^.*$!mailto:!"
 .
rfc3764.txt:   IN NAPTR 10 100 "u" "E2U+sip"    
"!^.*$!sip:!"
     .
rfc3824.txt:    IN NAPTR 100 10 "u" "E2U+sip"    
"!^.*$!sip:!"
     .
rfc3824.txt:    IN NAPTR 100 20 "u" "E2U+mailto" 
"!^.*$!mailto:!"
  .
rfc3953.txt:   IN NAPTR 100 10 "u" "E2U+pres" 
"!^.*$!pres:!"

In *all* of these examples, the regexp starts with "^" and ends with
"$", apparently to indicate that it should match the entire input
string (so that the entire input string can be replaced).

So it looks like the ISN system is not conformant with the definition
of NAPTR records right now, and we need to change the standard ISN
NAPTR record to:

*.xxx.freenum.org IN NAPTR 100 10 "u" "E2U+sip" \
        
"!^\\+*([^\\*]*).*$!sip:\\!"
 .

Dale