[bind10-dev] rrset trust level (Question about section 5.4.1 of rfc2181)

[Likun Zhang]

Hi all, 

I am still not very sure about my understanding for the following paragraph, which is in section 5.4.1 Ranking data of rfc2181), could you give some help?

   "Note that the answer section of an authoritative answer normally
   contains only authoritative data.  However when the name sought is an
   alias (see section 10.1.1) only the record describing that alias is
   necessarily authoritative.  Clients should assume that other records
   may have come from the server's cache.  Where authoritative answers
   are required, the client should query again, using the canonical name
   associated with the alias."

Make some messages as example

1. CNAME

Message example :

;HEADER
 AA QR
;QUESTION
  Example.com.  IN  NS
;ANSWER
  Example.com.  CNAME  example.org.
  Example.org.   CNAME  a.example.cn.
  a.example.cn.   NS     ns.example.cn.  

My understanding is:
  Only record "example.com. CNAME example.org." (the first record)  is treated as authoritative, the left two records in answer section are not authoritative, am I right here?

2. DNAME

Similar with CNAME, we have to deal with the situation when there are one or more DNAME records in answer section(I didn't find it in some rfc, including dname bits, but I think it should work like cname). Message example:

;HEADER
 AA QR
;QUESTION
  a.example.com.  IN  A
;ANSWER
  Example.com.    DNAME  example.org.
  a.example.com.  CNAME   a.example.org.
  Example.org.     DNAME  example.cn.
  a.example.org.   CNAME  a.example.cn.
  a.example.cn.    A      1.1.1.1

My understanding is:
 Only the first record in answer section is authoritative, all the left records are not authoritative, am I right here?

3. Last question (sorry for the long email, :) )
If there are some CNAME(DNAME) records in message's answer section, The first record must be CNAME(DNAME) record. Am I right here? or else, I think the message user don't know how to parse it. Is there some rfc talking about it?

	
Thanks
Likun