Re: How does RoundRobin flag work?
From: Roger Abell [MVP] (mvpNoSpam_at_asu.edu)
Date: 07/17/04
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Date: Fri, 16 Jul 2004 20:08:33 -0700
All that you describe seems correct behavior
When DNS returns multiple IPs, it is up to the client
application requesting the resolution to decide what
to do with the response.
more inlined . . .
"Peter Steele" <psteele@z-force.com> wrote in message
news:eCoeWT0aEHA.4092@TK2MSFTNGP10.phx.gbl...
> Okay, I've got it working, sort of. I created three A records for host
> "test" that represent the IP addresses of three existing systems in the
> same
> subnet (lets call them test1, test2, and test3). When I do a nslookup on
> test it returns a rotated list on each request.
yep, nslookup contains its own resolution code
> However, if I do a ping
> command, it always returns the same address unless I do a dnsflush between
> each ping.
Actually, DNS is only queried, and so it only returns anything on the
first try after the cache is flushed. If the earlier query is still cached
it is used without further work being done.
> I then tried opening a command prompt and entering the command
>
> dir \\test\c$
>
> and it came back with the error
>
> You were not connected because a duplicate name exists on the network.
> Go to System
> in Control Panel to change the computer name and try again.
>
> If I reference one of the systems directly, e.g. \\test1\c$, instead of
> using test, it has no problems accessing the system. As one final test, I
> went to Internet Explorer and entered the URL
>
> file://test/c$
>
> It said if could not find the file though, whereas
>
> file://test1/c$
>
> works fine.
>
those are NetBIOS-ish UNCs, and NetBIOS names are supposed
to be unique. Multihomed and NetBIOS has a long history of "maybe"s,
and even though this is no multihomed it has similarities.
What happens if you tried
\\test1.fulldomain.com\c$
??
> So, this feature isn't behaving the way I thought it would. Is this user
> error or correct behavior. Can I only take advantage of the feature
> programmatically?
>
These last test are behaviors exhibited by the client software, in
this case the network redirector for MS networking.
If what you are after is redundancy for fileshares, look at using DFS,
and/or network load-balancing of Windows server.
> "Roger Abell" <mvpNOSpam@asu.edu> wrote in message
> news:ebmsgosaEHA.596@TK2MSFTNGP11.phx.gbl...
>> A few points to keep in mind.
>> Client caching can get in the way of seeing the effect of
>> pseudo-roundrobin ordering. Use ipconfig /flushdns on
>> the client to empty the caching resolver's cache so that it
>> actually does really send the next query to the DNS server.
>> When there are multiple A records for a name, and the use
>> of pseudo-roundrobin ordering is enabled, then the list of
>> IPs returned will start a successive IPs with each query.
>> If other clients query the name in between two of your test
>> trials this will cause the IP ordering to advance accordingly.
>> If your test client is on the same subnet as one of the interfaces
>> of the DNS server, and one of the IPs for the name queried is
>> also on this subnet, and you have subnet ordering enabled in
>> the DNS server settings, then this will control what you see
>> returned as the IP list.
>> --
>> Roger Abell
>> Microsoft MVP (Windows Server System: Security)
>> MCSE (W2k3,W2k,Nt4) MCDBA
>> "Peter Steele" <psteele@z-force.com> wrote in message
>> news:%23jCVcpraEHA.3752@TK2MSFTNGP12.phx.gbl...
>> > I read that the Windows DNS supports a flag called RoundRobin which
>> > lets
>> you
>> > perform a primitive round-robin load balancing. Can anyone explain how
> to
>> > set this up? When I read this I thought it would work like this:
>> >
>> > ping mysystem.domain.com
>> > ...192.168.1.1
>> >
>> > ping mysystem.domain.com
>> > ...192.168.1.2
>> >
>> > ping mysystem.domain.com
>> > ...192.168.1.3
>> >
>> > and so on, returning a different address each time a DNS lookup has to
> be
>> > performed. I created multiple A records for a host and tried this
>> > though
>> but
>> > it always returned the first address in the list. If I do a nslookup on
>> the
>> > name, it returns all A addresses as a list.
>> >
>> > So how is this feature supposed to be used? Alternatively, if someone
> can
>> > suggest an alternative way to implement a simple round-robin load
>> balancing
>> > like this, I'd appreciate the advice.
>> >
>> >
>> >
>>
>>
>
>
- Next message: Roger Abell [MVP]: "Re: multiple ip addresses and default dns entries"
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