Varadhan Work <varadhan.w...@gmail.com> writes:
> Is it legal to have SIP domain name in SIP packet with only one single part
> without top level domain name ?
In both the general domain name syntax and in RFC 3261, section 25.1,
production "hostname" you can see that a domain name with only one label
is syntactically *legal*. So SIP URIs with such a domain name are
legal.
It is unlikely that such a URI will be usable, because it is rare that a
domain name with only one label has any DNS records defined for it
(other than NS and other DNS structural records). However, there has
been at least one exception: Fredrik Thulin once managed the nameserver
for .SE and added an MX record for .SE, directed to the host that
handled his e-mail. Thus, <fredrik@se> was a valid e-mail address for
him. Similar uses could be arranged for SIP.
In addition, in many situations, there is a convention that a domain
name that does not have a trailing "." will be passed to the DNS
resolver to search for using a provisioned list of suffixes. E.g., in a
host xyz.example.com, the suffix list may be "example.com" and "com",
allowing "abc" to be used to look up DNS records for abc.example.com.
In these situations, the trailing "." suppresses the lookups with
attached suffixes. In the case of SIP, the syntax allows the use of a
trailing ".":
hostname = *( domainlabel "." ) toplabel [ "." ]
However, I've never heard of a SIP system (intentionally) allowing the
use of provisioned suffixes in DNS lookups under any circumstances, and
skimming RFCs 3261 and 3263, I don't see any indication that it was
intended to allow it.
Dale
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