On May 28, 2010, at 8:55 AM, Ashwin wrote:
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.
Nope[0]
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.
Nope. resolvers can expect whatever they would like, but there is no
guarantee that the their expectations will be met. It seems that most
things do provide them in the "friendly" order, but I'm sure I have
seen them not as well...
W
Thanks & Regards
Ashwin
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