Subject: RE: [AVT] CNAME question

From: "Peter Barany" <[email-masked]>
Date: Wed, 11 Dec 2002 09:20:41 -0600

Colin,

Thanks for the reply. Just one more point/question. Regarding the use of
numeric address, the following is written in RFC 1889 (and RFC 1889bis):

"For example, the standard ASCII
   representation of an IP Version 4 address is "dotted decimal", also
   known as dotted quad. Other address types are expected to have ASCII
   representations that are mutually unique."

Regarding IPv6 addresses, the standard representation is (from RFC 2373 and
RFC 2373bis):

"The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the
      hexadecimal values of the eight 16-bit pieces of the address.
      Examples:

         FEDC:BA98:7654:3210:FEDC:BA98:7654:3210

         1080:0:0:0:8:800:200C:417A

      Note that it is not necessary to write the leading zeros in an
      individual field, but there must be at least one numeral in every
      field (except for the case described in 2.)."

If it is not too late, it might be a good idea to include this in RFC
1889bis as there might be some confusion about the "non-dotted decimal"
format of IPv6 addresses. Thanks.

Regards,

Pete

-----Original Message-----
From: Colin Perkins [mailto:[email-masked]]
Sent: Wednesday, December 11, 2002 7:52 AM
To: Barany, Peter [RICH1:2H16:EXCH]
Cc: [email-masked]'
Subject: Re: [AVT] CNAME question 

Hi,

--> "Peter Barany" writes:
>RFC 1889 (and the RFC 1889bis Internet draft) state that the use of the
>CNAME in RTCP SDES packets is mandatory.
>
>Regarding the format of CNAME, the following is written:
>
>The CNAME item SHOULD have the format "user@host", or "host" if a user name
>is not available as on single- user systems. For both formats, "host" is
>either the fully qualified domain name of the host from which the real-time
>data originates, formatted according to the rules specified in RFC 1034
[6],
>RFC 1035 [7] and Section 2.1 of RFC 1123 [8]; or the standard ASCII
>representation of the host's numeric address on the interface used for the
>RTP communication. 
>
>Question: Does this imply that there SHOULD be a DNS entry for the client
>(i.e., A/AAAA records that map FQDNs to IPv4/IPv6 addresses and PTR records
>that map IPv4/IPv6 addresses to FQDNs)? If so, does the IPv4/IPv6 source
>address of the RTCP packet (and associated RTP packets) have to match the
>DNS entry? Thanks.

RTP does not require the client to have a DNS entry, since the numeric
address can be used in the CNAME instead. Also, receivers cannot assume
that the source address of an RTCP packet matches the address in the CNAME
since the RTCP packet may have passed through an application level gateway.

Colin

---

From: Colin Perkins <[email-masked]>
Date: Wed, 11 Dec 2002 11:43:28 -0500

>format of IPv6 addresses. Thanks.

If you have specific, and minor, textual changes we might be able to
include then during the RFC publication process. I'm not convinced the gain
is worthwhile though, since the IPv6 address representation is well defined.

Colin
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