forwarding algorithm and timeouts

Bob Vance bobvance at
Tue Mar 27 19:00:06 UTC 2001

Thanks, Brad,
but, I think that you misinterpreted my question.

>Resolvers don't forward.  Name servers forward.

Of course, I know that.
   (although, when forwarding, it's basically doing the same
    thing -- sending  a recursive query -- but just not trying to
    append domain names, like resolvers typically do for nonFQDNs.

>>  I.e., do WinX or MAC clients also try their list initially with 5
>>  seconds, then re-do the list with 10 seconds, etc.?
>Nope.  They have resolvers, not name servers.
>Therefore, they do not forward.

Of course, here I was talking about the resolver routine searching its
nameserver list -- do Win9x and Mac clients follow the same resolver
algorithm laid out in 'DNS and BIND' for the Unix resolver.

I really had two questions in the post, which may have confused you:

1) for forwarding nameservers, what is the timeout used when trying each
server in the forwarders list?
I would assume that it must about the same as the resolver's first try,
which is 5 seconds, according to "the Book", because otherwise you could
queue up multiple forwarding requests for the same lookup, since the client
will try again after 5 seconds.

2) do all resolvers tend to follow the resolver algorithm in "the Book" and
is there any discussion of this in the RFCs?

Tks          |  BVance at
BV           |  BobVance at
Sr. Tech. Consultant,    SBM
Vox 770-623-3430         11455 Lakefield Dr.
Fax 770-623-3429         Duluth, GA 30097-1511

-----Original Message-----
From: Brad Knowles [mailto:brad.knowles at]
Sent: Tuesday, March 27, 2001 4:28 AM
To: bobvance at; bind-users at
Subject: Re: forwarding algorithm and timeouts

At 1:04 PM -0500 3/26/01, Bob Vance wrote:

>  Do all resolvers follow the algorithm described in 'DNS and BIND' ?

	Resolvers don't forward.  Name servers forward.

	Unfortunately, while name servers may contact a variety of name
servers to whom they are configured to forward queries, they will
only ever forward queries to one machine.

	The algorithm has changed slightly since the edition of the book
you're looking at -- I suggest that you do searches on the archives
of this mailing list to find out what the current algorithm is.

>  I.e., do WinX or MAC clients also try their list initially with 5
>  seconds, then re-do the list with 10 seconds, etc.?

	Nope.  They have resolvers, not name servers.  Therefore, they do
not forward.

Brad Knowles, <brad.knowles at>

/*        efdtt.c  Author:  Charles M. Hannum <root at>          */
/*       Represented as 1045 digit prime number by Phil Carmody         */
/*     Prime as DNS cname chain by Roy Arends and Walter Belgers        */
/*                                                                      */
/*     Usage is:  cat title-key scrambled.vob | efdtt >clear.vob        */
/*   where title-key = "153 2 8 105 225" or other similar 5-byte key    */

dig|perl -ne'if(/^x/){s/[x.]//g;print pack(H124,$_)}'

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