Round Robin DNS

[Jim Miller]

I want to implement RRDNS. I have created two A records
for a single hostname with 2 IP addresses. According to
what I have read from MS, to test this process, you do the
following:

Open a cmd prompt
type nslookup
type the hostname
the IP addresses should be listed 1 and 2
type the hostname again
the IP addresses should be listed as 2 and 1 now.

I have done this and it doesnt seem to be working. I have
checked to be sure the Enable RRDNS check box is checked
in the Advanced properties of the server. I am using AD
integrated DNS and have 4 AD servers. 3 are in one zone
and 1 in a separate zone.

Does anyone have any ideas as to why this does not appear
to be working?

Thanks

Jim Miller (MCP)

 

[Ace Fekay [MVP]]

In

I want to implement RRDNS. I have created two A records
for a single hostname with 2 IP addresses. According to
what I have read from MS, to test this process, you do the
following:

Open a cmd prompt
type nslookup
type the hostname
the IP addresses should be listed 1 and 2
type the hostname again
the IP addresses should be listed as 2 and 1 now.

I have done this and it doesnt seem to be working. I have
checked to be sure the Enable RRDNS check box is checked
in the Advanced properties of the server. I am using AD
integrated DNS and have 4 AD servers. 3 are in one zone
and 1 in a separate zone.

Does anyone have any ideas as to why this does not appear
to be working?

Thanks

Jim Miller (MCP)

You have to exit nslookup and reinitialize it, since it uses it's own cache.
You can test this if you have mutliple computers by a simple ping from each
one. You'll see that the different computers will get a different response.
I've demonstrated this in a classroom environment since we would normally
have 12 machines. I would have all the students ping the name at the same
time and different responses would appear, as expected. Round RObin is
enabled by default.




--
Regards,
Ace

Please direct all replies to the newsgroup so all can benefit.
This posting is provided "AS IS" with no warranties.

Ace Fekay, MCSE 2000, MCSE+I, MCSA, MCT, MVP
Microsoft Windows MVP - Active Directory

 

[Jeff Westhead [MS]]

Actually it should work fine from nslookup. There is no cache in nslookup.
Are the two IP addresses in different class C subnets?

D:\>nslookup - 127.0.0.1
Default Server: localhost
Address: 127.0.0.1

host.bigzone.com.

Server: localhost
Address: 127.0.0.1

Name: host.bigzone.com
Addresses: 1.1.1.1, 2.2.2.2

host.bigzone.com.

Server: localhost
Address: 127.0.0.1

Name: host.bigzone.com
Addresses: 2.2.2.2, 1.1.1.1

--

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


"Ace Fekay [MVP]"

 

[Ace Fekay [MVP]]

In

Actually it should work fine from nslookup. There is no cache in
nslookup. Are the two IP addresses in different class C subnets?

D:\>nslookup - 127.0.0.1
Default Server: localhost
Address: 127.0.0.1

Server: localhost
Address: 127.0.0.1

Name: host.bigzone.com
Addresses: 1.1.1.1, 2.2.2.2

Server: localhost
Address: 127.0.0.1

Name: host.bigzone.com
Addresses: 2.2.2.2, 1.1.1.1

Good point!

--
Regards,
Ace

Please direct all replies to the newsgroup so all can benefit.
This posting is provided "AS IS" with no warranties.

Ace Fekay, MCSE 2000, MCSE+I, MCSA, MCT, MVP
Microsoft Windows MVP - Active Directory

 

[Jonathan de Boyne Pollard]

JM> According to what I have read from MS, to test this process,
JM> you do the following:
JM>
JM> Open a cmd prompt
JM> type nslookup
JM> type the hostname
JM> the IP addresses should be listed 1 and 2
JM> type the hostname again
JM> the IP addresses should be listed as 2 and 1 now.

Those instructions are erroneous in two ways:

1. Don't use "nslookup". It is a highly flawed tool and its
avoidance is recommended by almost everyone. There are better
DNS diagnosis tools available. Use them.

2. The missing step between the fourth and fifth steps that
you list is "wait for the TTL period".

 

[Jim Miller]

Here is what nslookup looks like:

nslookup
Default Server: DNSserver.mydomain.com
Address: 10.1.5.1

terminalvm

Server: DNSserver.mydomain.com
Address: 10.1.5.1

Name: virtualname.mydomain.com
Addresses: 10.1.5.60, 10.1.5.30


We run a class B subnet, 255.255.0.0. It makes no
difference if I exit nslookup or not. I always get the
same IP listed first.

Thanks for your help.

Jim

 

[Jason Meyer]

All nslookup is doing is sorting the address, from what it looks like is
biggest to smallest. A real test would be to have some layer 7 app do
lookups and see what gets returned. If its a webserver just browse a
website, maybe use a server var to display which address you are hitting.
Actually I bet ping will do the same thing, but you probably will have to
get a couple machines going to see it in action. Hope this helps.

Jason

 

[Jeff Westhead [MS]]

If you have "Enable netmask ordering" in the DNS server properties (Advanced
tab) checked, try unchecking it.

 

[Jim Miller]

Jeff,

Thanks, that is exactly what I needed to do. Now it is
working just like it should.

Jim

 

[Jeff Westhead [MS]]

FYI, in W2K3 netmask ordering and round robin do a better job of working
together.