DHCP server hanging out .0's and .255's

[Tekmazter]

Okay, I haven't created any new scopes lately so this I thought was
something new. All of the sudden my dhcp server is handing out leases to .0
and .255 addresses on my scope. I thought DHCP was aware that it couldn't
hand these out?

 

[Herb Martin]

Okay, I haven't created any new scopes lately so this I thought was
something new. All of the sudden my dhcp server is handing out leases to ..0
and .255 addresses on my scope. I thought DHCP was aware that it couldn't
hand these out?

No, they should never have been included in the
scope (or included but excluded explicitly.)

The good news if that you can exclude them without
reconfiguring the scope.

 

[Phillip Windell]

It can't. It won't even allow you to put the in the IP# range to begin
with. However if you have an incorrect mask it will let you include them in
the range if the mask causes those to not really be the ID and BCast
addresses.

For example if had the range 192.168.5.0 - 192.168.5.255 and you mistakenly
used 255.255.0.0 instead of 255.255.255.0, the the ID and BCast would be
192.168.0.0 & 192.168.255.255 instead of the normal 192.168.5.0 &
192.168.5.255

 

[Phillip Windell]

It should not even let it be entered in the Range to bein with unless the
Mask is wrong, at least the MS DHCP is that way,...I don't know about other
Vendors.

 

[Herb Martin]

It should not even let it be entered in the Range to bein with unless the
Mask is wrong, at least the MS DHCP is that way,...I don't know about other
Vendors.

I THINK (not certain) that I have seen SOME versions
of the Microsoft DNS server allow those to be entered.

I am perfectly willing to believe that there might be other
versions (or SPs) that disallow it, and I might even be
wrong, but he seems to have done this and this and I do
have a vague memory of fixing this (live) for someone
in the past.

 

[Michael D. Ober]

It will of the .0 and .255 addresses are inside the netmask. In this case,
it's perfectly legal to hand them out. What's not legal is to hand out
addresses that resolve to your netmask. For example:

Netmask: 255.255.0.0
Base address: 192.168.0.0

Illegal: 192.168.0.0 - this is the network addrress
Illegal: 192.168.255.255 - this is the broadcast address

Legal: 192.168.15.0
Legal: 192.168.25.255

Mike Ober.

 

[Tekmazter]

Well I went ahead and configured the scope to explicitly deny those
addresses. I'll check out the scope mask and everything else as soon as I
get a chance. There is a possibility it was cofigured wrong to begin with.
I only recently took over as the new netadmin here.

Thanks for all the replies guy's and I'll post back if the mask was the
issue.

 

[Tekmazter]

Okay guy's here is my current scope setup:

starting address:10.100.0.1
ending address: 10.100.3.254
mask: 255.255.252.0

The address the user got when I noticed it handing out .0's was that of
10.100.2.0
It was also at this time that I noticed another machine which got
10.100.2.255

The user which received .0 had just gone through a lease expiration and was
got this upon renewal. She could no longer access network resources until I
put her on something else. I just flushed the .255 and then went and
explicitly denied those IP's from be handed out.

Thoughts?

 

[Herb Martin]

Okay guy's here is my current scope setup:

starting address:10.100.0.1
ending address: 10.100.3.254
mask: 255.255.252.0

The address the user got when I noticed it handing out .0's was that of
10.100.2.0

Well, that is NOT a "zero" address with THAT NetMask.

It is the 2.0 host of the 10.100.0 subnet.

Perfectly legal address with that mask.

It was also at this time that I noticed another machine which got
10.100.2.255

Also perfectly legal. Someone has taught you
the wrong rule -- 0 and 255 in an OCTECT are
NOT automatically "bad" (nor are non-zero in
an octet autmatically "good".)

That is only true with the DEFAULT CLASS C
mask of 255.255.255.0

The user which received .0 had just gone through a lease expiration and was
got this upon renewal. She could no longer access network resources until I
put her on something else. I just flushed the .255 and then went and
explicitly denied those IP's from be handed out.

There is NO NEED to do that as those addresses are
perfectly fine (with that mask.)

 

[Phillip Windell]

Okay guy's here is my current scope setup:

starting address:10.100.0.1
ending address: 10.100.3.254
mask: 255.255.252.0

The address the user got when I noticed it handing out .0's was that of
10.100.2.0
It was also at this time that I noticed another machine which got
10.100.2.255

Yep, that is exactly what I thought was going on. Thoses addresses are
perfectly find for that. the "0" and "255" addresses that you don't want
are 10.100.0.0 and 10.100.3.255 and those won't happen because they aren't
in the range, just like I said.

BTW - You can't change the mask in an exisiting scope,...you'd have to
delete the scope and recreate it. Unless there is a good reason to do
otherwise, just leave it alone, it will work fine as it is.

 

[Tekmazter]

Hey guy's this would be why I was confused then...

Originally I thought that this would be fine ... obviously for my network
range 10.100.0.0 would be illegal. I guess the fact that her having that
address and just losing network connectivity right after she had obtained it
threw me off.

Well, I appreciate all of you who have responded.

 

[Herb Martin]

Hey guy's this would be why I was confused then...

Originally I thought that this would be fine ... obviously for my network
range 10.100.0.0 would be illegal.

Right because it is the lowest (or zero address) in the
range, not (merely) because it has some zeroes in it.

I guess the fact that her having that
address and just losing network connectivity right after she had obtained it
threw me off.

And I made the mistake of answering the actual question
you asked (solely) and not interpreting it a bit as is my
usual practice.

Normally, I try to give more than "just the answer" to
such questions.

 

[Tekmazter]

No sweat. Fortunately enough for me, being an idiot is only intermittent

Good luck to ya!