Disabling Round Robin Not Working Correctly

[Calvin Miles]

I have my .dns file configured as follows:

;
; Zone records
;

server1 A 172.29.255.27
A 10.224.252.254
A 172.29.27.1

The way I understand it (according to the DNS help file
even), disabling round-robin should cause DNS to return:
172.29.255.27 as the address. Instead it always returns
10.224.252.254 (the lowest IP address).

Is anyone else seeing this? Anyone have a work around to
get DNS to work how the documentation says it should work
with round robin disabled?

Thanks!

Calvin

 

[Marc Reynolds [MSFT]]

Hi Calvin,


From what IP address are you sending the query? You could be seeingthe
effects of Local Net Priority.

LocalNetPriority
----------------


Value: LocalNetPriority
Added: SP4
Type: DWORD (Boolean)
Default: NoKey (Give local net records priority)
Function: Determine the priority of multiple A records given in
response.

By default, the Microsoft DNS server gives priority to the
"closest" A record to the client's IP address when there are multiple A
records
for a name. This is designed so that the client application will
attempt to
connect to the closest (and fastest) IP available.

Example:
www.samples.microsoft.com has three A records: 198.27.1.1, 20.23.25.1,
and
131.21.31.7. Client at 131.21.198.25 queries DNS server for
www.samples.microsoft.com. Instead of returning in database order or
round
robin, the DNS server notices that the client's 131.21 address matches
the
network (class B) portion of the 131.21.31.7 address. The DNS server
then
reorders the addresses in the response:

131.21.31.7
198.27.1.1
20.23.25.1

If the client query comes from 12.123.248.12, then none of
addresses matches in the network portion of the address and NO local net
priority reordering is done.

If more than one address matches in the
network portion, then the matching addresses are ordered with the
closest match
first so that the result is most likely to be correct regardless of any
subnetting.

Example: www.samples.microsoft.com has four A records:
198.27.1.1, 20.23.25.1, 131.21.31.7, and 131.21.196.8. Client at
131.21.198.25
queries DNS server for www.samples.microsoft.com. Now both 131.21
addresses are
returned at the top, but the 131.21.196 address is first because it
matches the
client's IP address down through the 131.21.192 subnet (that is, it
would match
even if subnetting down to a 255.255.248 mask). So the response is
ordered:


131.21.196.8
131.21.31.7
198.27.1.1
20.23.25.1

NOTE: Having LocalNetPriority supersedes round robining.
However, if RoundRobin is on, the records continue to be round-robined,
and are
returned in the current round-robin order when no LocalNetPriority
match can be
made.

Thanks,
Marc Reynolds
Microsoft Technical Support

This posting is provided "AS IS" with no warranties, and confers no rights.

 

[William Stacey]

The client may also do net priority I think.

 

[Calvin Miles]

I'm querying from 172.30.252.29.. which makes it even
more strange as to why its returning the 10.224.252.252
address.

The client is actually a Cisco Router, so it knows
nothing about local net priority.

Any other ideas? Server is Windows 2000 SP3.

Thanks!

Calvin

-----Original Message-----
Hi Calvin,


From what IP address are you sending the query? You could be seeingthe
effects of Local Net Priority.

LocalNetPriority
----------------


Value: LocalNetPriority
Added: SP4
Type: DWORD (Boolean)
Default: NoKey (Give local net records priority)
Function: Determine the priority of multiple A records given in
response.

By default, the Microsoft DNS server gives priority to the
"closest" A record to the client's IP

address when there are multiple A

records
for a name. This is designed so that the client application will
attempt to
connect to the closest (and fastest) IP available.

Example:
www.samples.microsoft.com has three A

records: 198.27.1.1, 20.23.25.1,

and
131.21.31.7. Client at 131.21.198.25 queries DNS server for
www.samples.microsoft.com. Instead of returning in database order or
round
robin, the DNS server notices that the

client's 131.21 address matches

the
network (class B) portion of the

131.21.31.7 address. The DNS server

then
reorders the addresses in the response:

131.21.31.7
198.27.1.1
20.23.25.1

If the client query comes from 12.123.248.12, then none of
addresses matches in the network

portion of the address and NO local net

priority reordering is done.

If more than one address matches in the
network portion, then the matching addresses are ordered with the
closest match
first so that the result is most likely

to be correct regardless of any

subnetting.

Example: www.samples.microsoft.com has four A records:
198.27.1.1, 20.23.25.1, 131.21.31.7, and 131.21.196.8. Client at
131.21.198.25
queries DNS server for

www.samples.microsoft.com. Now both 131.21

addresses are
returned at the top, but the 131.21.196 address is first because it
matches the
client's IP address down through the 131.21.192 subnet (that is, it
would match
even if subnetting down to a

255.255.248 mask). So the response is

ordered:


131.21.196.8
131.21.31.7
198.27.1.1
20.23.25.1

NOTE: Having LocalNetPriority supersedes round robining.
However, if RoundRobin is on, the

records continue to be round-robined,