IP addressing question

[Michael Silverman]

Hello all,

Changed our network addressing last night...

We had the following:

10.x.x.x/16 and our Win2K SP4 DHCP server was handing out 10.0.0.1 through
10.0.0.254

We changed the DHCP server to hand out 10.0.0.1 through 10.0.3.255 and
excluded 10.0.1.0 through 10.0.2.255

Reason was we wanted all the DHCP clients to change from 10.0.0.x to
10.0.3.x so that we could use the lower addresses for other devices.

This apparently did not work well, while some hosts were able to be reached,
specifically the two AD/DNS/DHCP servers were hit and miss, mostly miss.

Did I miss something at the school of networking here or is this a "windows
feature"?

Thanks for any input.

Mike.

 

[Phillip Windell]

We changed the DHCP server to hand out 10.0.0.1 through 10.0.3.255 and
excluded 10.0.1.0 through 10.0.2.255
Reason was we wanted all the DHCP clients to change from 10.0.0.x to
10.0.3.x so that we could use the lower addresses for other devices.

That should have worked, however the standard way to do this would be for
the DHCP Scope to contain the entire IP Range (10.0.0.1 -- 10.0.255.255 for
a 16bit mask) and then use exclusions to control what addresses are actually
given out. This way you can change it at any time by altering the exclusions
without having to delete and re-create the scope itself.

This apparently did not work well, while some hosts were able to be reached,
specifically the two AD/DNS/DHCP servers were hit and miss, mostly miss.

Are you saying that the AD/DNS/DHCP servers aren't using static addresses?
What "some host"? Please be specific. Is the DHCP Server's Mask in
agreement with the one in the scope? What Mask is the DHCP Clients actually
receiving?

 

[Michael Silverman]

That should have worked, however the standard way to do this would be for
the DHCP Scope to contain the entire IP Range (10.0.0.1 -- 10.0.255.255 for
a 16bit mask) and then use exclusions to control what addresses are actually
given out. This way you can change it at any time by altering the exclusions
without having to delete and re-create the scope itself.

Changed it to 10.0.255.254 (can't use the subnet broadcast address as the
end value for the scope)

Are you saying that the AD/DNS/DHCP servers aren't using static addresses?
What "some host"? Please be specific. Is the DHCP Server's Mask in
agreement with the one in the scope? What Mask is the DHCP Clients actually
receiving?

The AD servers are using static addresses and the subnet mask is identical
on all machines. I was referrring to the clients that were getting DHCP
addresses that were not able to connect to the AD servers. However they
were able to communicate with other servers such as our Citrix, Unix,
windows member servers, all of which are only 1 IP address apart basically.

I have a PC that I am using as a test machine with a static address in the
10.0.3.x range and it still exhibits the same communication issues. I am
going to sniff the traffic when I get a chance.

Mike.

 

[Phillip Windell]

Changed it to 10.0.255.254 (can't use the subnet broadcast address as the
end value for the scope)

Ah! Yes,...sorry....

I have a PC that I am using as a test machine with a static address in the
10.0.3.x range and it still exhibits the same communication issues. I am
going to sniff the traffic when I get a chance.

Ok, that sounds good. Using a static machine pretty much shows that this
isn't any kind of DHCP issue.

 

[Michael Silverman]

Ah! Yes,...sorry....


Ok, that sounds good. Using a static machine pretty much shows that this
isn't any kind of DHCP issue.

Right. I figure it is something on the network that may be interfering with
the traffic but I won't be able to tell until I can watch exactly what the
traffic is. We also have some managed switches but they have not been set
up yet for IP communication. One of my many upcoming projects here.

Thanks for the input. If anyone thinks of anything else, I am more than
willing to hear it. I will update when I can on this "bizarre" issue.

Mike.

 

[Doug Sherman [MVP]]

"excluded 10.0.1.0 through 10.0.2.255"

Did you mean 10.0.0.1 through 10.0.2.255?

This might contribute to the problem if you have static addresses which are
not excluded from the scope.

Doug Sherman
MCSE Win2k/NT4.0, MCSA, MCP+I, MVP

 

[Mike Silverman]

Sorry, yes I meant 10.0.0.1 through 10.0.2.255.

"excluded 10.0.1.0 through 10.0.2.255"

Did you mean 10.0.0.1 through 10.0.2.255?

This might contribute to the problem if you have static addresses which are
not excluded from the scope.

Doug Sherman
MCSE Win2k/NT4.0, MCSA, MCP+I, MVP