- The use of "+" in lookups is confusing, and warrants further
explanation. All E.164 numbers ("global phone numbers") by
definition need a leading "+" during ENUM lookup. If you neglect to
add a leading "+", you may discover that numbers that seem to exist
in the DNS aren't getting matched by the system or are returned with
a null string result. This is due to the NAPTR reply requiring a
"+" in the regular expression matching sequence. Older versions of
Asterisk add a "+" from within the code, which may confuse
administrators converting to the new function. Please ensure that
all ENUM (e164.arpa) lookups contain a leading "+" before lookup, so
ensure your lookup includes the leading plus sign. Other DNS trees
may or may not require a leading "+" - check before using those
trees, as it is possible the parsed NAPTRs will not provide correct
results unless you have the correct dialed string. If you get
console messages like "WARNING[24907]: enum.c:222 parse_naptr: NAPTR
Regex match failed." then it is very possible that the returned
NAPTR expects a leading "+" in the search string (or the returned
NAPTR is mis-formed.)
- If a query is performed of type "c" ("count") and let's say you
get back 5 records and then some seconds later a query is made
against record 5 in the list, it may not be the case that the DNS
resolver has the same answers as it did a second or two ago - maybe
there are only 4 records in the list in the newest query. The
resolver should be the canonical storage location for DNS records,
since that is the intent of ENUM. However, some obscure future
cases may have wildly changing NAPTR records within several seconds.
This is a corner case, and probably only worth noting as a very rare
circumstance. (note: I do not object to Asterisk's dnsmgr method of
locally caching DNS replies, but this method needs to honor the TTL
given by the remote zone master. Currently, the ENUMLOOKUP function
does not use the dnsmgr method of caching local DNS replies.)
- If you want strict NAPTR value ordering, then it will be
necessary to use the "ALL" method to incrementally step through the
different returned NAPTR pointers. You will need to use string
manipulation to strip off the returned method types, since the
results will look like "sip:12125551212" in the returned value.
This is a non-trivial task, though it is required in order to have
strict RFC compliance and to comply with the desires of the remote
party who is presenting NAPTRs in a particular order for a reason.
- Default behavior for the function (even in event of an error) is
to move to the next priority, and the result is a null value. Most
ENUM lookups are going to be failures, and it is the responsibility
of the dialplan administrator to manage error conditions within
their dialplan. This is a change from the old app_enumlookup method
and it's arbitrary priority jumping based on result type or failure.
- Anything other than digits will be ignored in lookup strings.
Example: a search string of "+4372030blah01721" will turn into
1.2.7.1.0.0.3.0.2.7.3.4.e164.arpa. for the lookup. The NAPTR
parsing may cause unexpected results if there are strings inside
your NAPTR lookups.
- If there exist multiple records with the same weight and order as
a result of your query, the function will RANDOMLY select a single
NAPTR from those equal results.
- Currently, the function ignores the settings in enum.conf as the
search zone name is now specified within the function, and the H323
driver can be chosen by the user via the dialplan. There were no
other values in this file, and so it becomes deprecated.
- The function will digest and return NAPTRs which use older
(deprecated) style, reversed method strings such as "sip+E2U"
instead of the more modern "E2U+sip"
- There is no provision for multi-part methods at this time. If
there are multiple NAPTRs with (as an example) a method of
"E2U+voice:sip" and then another NAPTR in the same DNS record with a
method of ""E2U+sip", the system will treat these both as method
"sip" and they will be separate records from the perspective of the
function. Of course, if both records point to the same URI and have
equal priority/weight (as is often the case) then this will cause no
serious difficulty, but it bears mentioning.
- ISN (ITAD Subscriber Number) usage: If the search number is of
the form ABC*DEF (where ABC and DEF are at least one numeric digit)
then perform an ISN-style lookup where the lookup is manipulated to
C.B.A.DEF.domain.tld (all other settings and options apply.) See
http://www.freenum.org/ for more details on ISN lookups. In the
unlikely event you wish to avoid ISN re-writes, put an "n" as the
first digit of the search string - the "n" will be ignored for the search.
lmadsen
2010-01-14
