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scouture2001 Absent Member.
Absent Member.
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Question about Forward List mechanism

Hi there,

My DNS server recently behave incorrectly, at least to my comprehension. First, here's my setup:

My DNS servers have a forward list of 3 servers, the 2 first can resolve names of a larger intranet+internet, the last can only resolve internet names. It appears that dns requests were forwarded not only to the first one but to any of them, producing unresolved requested when a request for the intranet why submitted to the 3rd server of the forward list.

I've always thought DNS servers were forwarding the request to the first server of the list and if this server wasn't responding, it would forward to the second, and so on.

I've installed ethereal and it shows that they are all used, not only the first in the list.

I've found an option in iManager (forward: first or only) I've never seen before (was using DNS/DHCP Console and this option is in another tab, burried with many other options) and though I haven't touched it (left to "first") I wondered if this could explain this behaviour.

Anyone have an clear explanation of this option, or hint of what's happening to my DNS servers?

BTW: servers are SLES10SP3 with OES2SP2

Serge
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scouture2001 Absent Member.
Absent Member.

Re: Question about Forward List mechanism

Okay, I found that all forwarders are considered equals (no priority), thus it's ok to see requests being forwarded to everyone of them.

Concerning the forwarders, they should all be able to resolve requests (no restriction on which domain is being requested). Which isn't my situation. I should configure a zone for the Intranet and point the 2 forwarders that are able to resolve and then configure the forwarders of the servers ("last resort") with my 3 original ones.

*Solved*
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joharmon Absent Member.
Absent Member.

Re: Question about Forward List mechanism

That was quick. I was going to reply after I did some testing. Here was my results:

We don't appear to round robin. It appears we start at the top of the list for the first query, and move down the list until we get an answer. The next query starts with the successful server (the one we successfully received a DNS response from), and only moves on in the list if that one doesn't work for the next query. In the middle of my testing my server went to the root servers too. I don't think there is a solid enough pattern here to determine anything other than we don't have a guaranteed order that we will use.

If you click on the help button under the DNS/DHCP mgmt console, or iManager, you can get details about what the "first" and "only" settings do.
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