Regarding CNAME Chains

Ashwin ashwins at huawei.com
Fri May 28 12:55:17 UTC 2010


 

 Hi, 

 

  From the server I get a response like

 

            aaa CNAME bbb

            ccc CNAME ddd

            bbb CNAME ccc

 

The ordering of the CNAME chain is incorrect, ideally it should be like

 

            aaa CNAME bbb

            bbb CNAME ccc

            ccc CNAME ddd

 

Is there some RFC which prohibits the configuration of CNAME chains as given
in the first example, ie CNAME chains not in order.

 

I tried to search on the internet, and could come up with this para in RFC
2308: DNS NCACHE

 

"QNAME" - the name in the query section of an answer, or where this resolves
to a CNAME, or CNAME chain, the data field of the last CNAME. The last CNAME
in this sense is that which contains a value which does not resolve to
another CNAME. Implementations should note that including CNAME records in
responses in order, so that the first has the label from the query section,
and then each in sequence has the label from the data section of the
previous (where more than one CNAME is needed) allows the sequence to be
processed in one pass, and considerably eases the task of the receiver. 



It would be a great help if it can be confirmed that resolvers can expect
CNAME chains to be in order.

 

Thanks & Regards

Ashwin

 

 

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