Re: Running out of IP addresses

"Maurice Bishop" <no.spam.here.please@xxxxxxxxxxxxxxxxxx> wrote in message
news:13krkn1hts7jdf5@xxxxxxxxxxxxxxxxxxxxx
I am running out of useable IP addresses on my subnet.

I have a network of 5 servers running Windows 2003 server on the same
domain, one of which runs DHCP for the whole network on one subnet. There
are approximately 110 client computers. In total, with workstations,
servers, routers, print servers, multi function devices etc, there are
about 220 IP addresses used on the LAN.

First. Scopes should always include the entire address range (*.1-*.254)
then control it with Exclusions.

The subnet has 254 possible addresses,...there is no way you would run out.
You still have 35 left over even if every single device was powered up and
running all at the same time.

I cannot extend the present scope to include IP addresses above 130 as I
have static address assignments above 130 that cannot be moved without a
considerable amount of hassle.

Go around them. If they are sequential them mark them out with an Exclusion.
You probably have a chunk of addresses above them that aren't used. They
can be added to the dynamic group of addresses by simply not including them
in an Exclusion. In other words when you exclude 130 an up you don't have
to go all the way to 254. I actually have two distinct Exclusion ranges in
mine.

Can I change the subnet to 255.255.0.0 and start to use a second scope of
192.168.2.10 thru 192.168.2.254 ?

No.

1. It would go in the same scope,..not a new scope. But since you cannot
edit a Scope in that way you would have to delete the existing one and
create and entirely new one for the whole thing. That could be a lot of
work if their are a lot of Scope Options or Reservations,...and there would
be no DHCP available during the period that this was being performed.

2. Ethernet is not supposed to have subnets bigger than 254 hosts.
Efficiency starts to drop off due to broadcasts at around 250 to 300 hosts
depending on the type of traffic already on the wire.
"But a lot of people are doing it!",...yes and a lot of networks perform
like crap when they are hit with a "real" load and they will blame
everything except the real cause. Some are just lucky because they don't
generate a lot of traffic to start with, so the problem is "unnoticed". Some
have big subnets but simply have not actually filled them up with *too many*
host,...at least not yet.

Faster systems (like gigabit) just aren't noticable to the human perception
that early on because most people would never notice a gigbit network that
actualy only performs like a 100 or 10 mbps system until something "stressed
it" or it was measured with equipment. But if you want a gigabit system to
actually run at gigabit speed,..the same rules apply.

To go more than 254 hosts,...create a whole new subnet and put a LAN Router
between them. You can build it first and get it working with no machines
even on it. Then gradually over time start moving some things over to it as
is becomes convienient. If you create a new 254 host segment then you will
have a 508 host capacity and won't run into trouble with broadcast and will
be able to grow and double in size without any topology changes at all.
Don't forget to install WINS on at least one server and use it. Some things
still require netbios resolution and WINS is required for it to function
across routers.

--
Phillip Windell
www.wandtv.com

The views expressed, are my own and not those of my employer, or Microsoft,
or anyone else associated with me, including my cats.
-----------------------------------------------------


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