Running out of IP addresses on subet

[Brett Charlton]

Hi

I wonder if someone can point me in the right direction please. Our
single subnet Windows 2000 LAN is running out of IP addresses (i.e.
we're approaching 255 clients). Can someone tell me the best practice
method for increasing the IPs available on my LAN? i.e. should we
bridge? should we route? what should we do?

Apologies for the newbie question

Regards

BC

 

[Doug Sherman [MVP]]

Assuming you use DHCP - The least dislocation for existing clients is to add
a new subnet. To do this you need a router that provides DHCP Relay, or you
can install a new DHCP server on the new subnet, or you can make your
existing DHCP server a router by installing a second NIC.

The second least dislocation is to delete the scope and recreate it with a
different subnet mask that allows for more hosts - eg. 192.168.1.0
255.255.0.0. If you do this, you will have to manually change the mask on
your servers and other statically configured machines.

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

 

[Doug Sherman [MVP]]

I guess the example should have been: eg. 192.168.0.0
255.255.0.0

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

 

[PinkY]

I guess the example should have been: eg. 192.168.0.0
255.255.0.0

what about superscope?
I have simillar situation that our network is A class with 22 bit subnet
mask (255.255.252.0) and we are moving to one physical location (one
physical subnet) with about 1500 hosts
we thought of creating few logical subnets (10.1.4.0, 10.1.8.0 etc.)
how do you see solution of our problem?
tnx

 

[Phillip Windell]

A Superscope could work if you do it carefully. But you'll have to
delete/recreate the Scope since you would need a different mask and you can
not alter the mask in a Scope. Since you would be deleting the scope
however, you might as well just create the new Scope with the full range and
mask you need in a single Scope, which means you wouldn't need a Superscope.

I still think you would be better off to just use multiple 254 hosts (24
bit) subnets and be done with it. that will also keep you at or under the
250 hosts per-subnet number which would keep the network efficient.

--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com

 

[Doug Sherman [MVP]]

Superscopes and supernetting are two different things - see:

http://support.microsoft.com/kb/q186341/

You have two issues here:

1. If all logical subnets have a mask of 255.255.252.0, where would a
10.1.4.0 machine send packets destined for a 10.1.8.0 address? You could
assign 2 IP addresses to the adapter on a statically configured shared
resource, but this quickly becomes clunky and unmanageable.

2. It depends on bandwidth and traffic volume, but most people would
recommend physically segmenting a 1500 machine network in order to reduce
broadcast traffic.

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

 

[bcharlton]

Unfortunately I've inherited a network without DHCP - all clients are
statically assigned along the range 192.9.101.x / 255.255.255.0.
Therefore changing the subnet mask would require me to change all
client configs. Can I simply install a second NIC in a W2K member
server, assign the 2nd NIC 192.9.102.x / 255.255.255.0 and use the W2K
Server as a router?? The 2nd subnet would still be on the same
physical wire. WIll this be an issue?

Regards

BC

 

[Doug Sherman [MVP]]

250+ machines with static addresses - yuck.

1. Yes, you could add a NIC to the server and enable routing. BUT, there
is little point in doing this unless you get a second switch and connect the
server's second NIC and all machines on the new subnet to the new switch.

2. Don't know how many of your machines really 'need' static IPs -
obviously DCs and other servers sharing resources. Now might be a good time
to consider converting to DHCP. You can do this with a script:

netsh interface ip set address "Local Area Connection" dhcp

You can also configure static IPs with a script - See:

http://support.microsoft.com/default.aspx?scid=kb;en-us;257748

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

 

[bcharlton]

I know, its a real headache! Clients don't really need to be static.
Got a bunch of Jet Direct units that our HPUX box addresses directly
via IP which need to stay static in the short-term. Other than that
can probably go DHCP on clients. Thanks for the pointers to the
scripts. I think this and your original idea to resubnet is the way to
go. Many thanks. BC

 

[Michael D. Ober]

I would go one further and use the DHCP reservation system for those clients
that need to remain static and let DHCP manage all non-server equipment.
The JetDirect cards are excellent candidates for DHCP reservations.

Mike Ober.

 

[PinkY]

A Superscope could work if you do it carefully. But you'll have to
delete/recreate the Scope since you would need a different mask and you can
not alter the mask in a Scope. Since you would be deleting the scope

well, that was obvious and no problem with it

however, you might as well just create the new Scope with the full range and
mask you need in a single Scope, which means you wouldn't need a

Superscope.

I think it would be pretty complicated to manage a 1500 hosts scope,
wouldn't it?

I still think you would be better off to just use multiple 254 hosts (24
bit) subnets and be done with it. that will also keep you at or under the
250 hosts per-subnet number which would keep the network efficient.

that was my first and easiest solution and I think that it is a winner
why complicate things where you don't need it complicated
I just thought that it is best practise or recommended feature to go with
superscope
tnx

 

[PinkY]

1. If all logical subnets have a mask of 255.255.252.0, where would a
10.1.4.0 machine send packets destined for a 10.1.8.0 address? You could
assign 2 IP addresses to the adapter on a statically configured shared
resource, but this quickly becomes clunky and unmanageable.

via default gw, where else
it works fine now

2. It depends on bandwidth and traffic volume, but most people would
recommend physically segmenting a 1500 machine network in order to reduce
broadcast traffic.

well, physicall segmenting is more expensive to do then logical
the solution we are going for is switches with vlans and dhcp relay agents
at switches so that only broadcast traffic would be dhcp request
it looks simple enough

 

[Doug Sherman [MVP]]

Didn't know you had VLan capability - yes, you can manage this with multiple
scopes on a single DHCP server. Don't know that there is any need for
superscopes though.

If you did not have VLans, the subnets would not be able to communicate.

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

 

[Doug Sherman [MVP]]

One final thought - see response to PinkY above. With 250+ machines, you
may already be using suphisticated managed switches. If this is the case,
check your switch documentaion - you may have VLan capability and this would
allow you to configure logical subnets and routing on a single physical
segment. eg. see:

http://cisco.com/en/US/products/hw/...figuration_guide_chapter09186a0080160a7c.html

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

 

[Phillip Windell]

I think it would be pretty complicated to manage a 1500 hosts scope,
wouldn't it?

No it wouldn't be a problem at all.
Six scopes would handle it just fine depending on how you design the
network. I can't cover all possible designs in a NG message, but....

6 subnets/scopes x 254 hosts per each = 1524 Hosts

10.1.0.0/24 = 254 usable Hosts
10.1.1.0/24 = 254 usable Hosts
10.1.2.0/24 = 254 usable Hosts
10.1.3.0/24 = 254 usable Hosts
10.1.4.0/24 = 254 usable Hosts
10.1.5.0/24 = 254 usable Hosts
10.1.6.0/24 = 254 usable Hosts

I run 5 scopes here with the potential of 8,...I just didn't create scopes
for the other 3 IP Ranges that I haven't put into service, but everything is
pretty much ready to go if I need them.

We use:
Router/Switch combo = HP 5304XL
This can handle more subnets that you would care to create. It is the
logical "center" of the LAN and its Subnet,... like a "hub and spoke" with
the router being the "hub".
On the end of the "spokes" we run HP2524 Switches and the Subnet Segments
are a blend of VLAN and physical segments that mostly follow the "spokes".

I run duel DHCP servers, identically configured (except for Exclusions),
that both reside only the first Subnet,..the HP5304XL relays the DHCP
Queries to the DHCP Server on behalf of the other subnets.

 

[Phillip Windell]

well, physicall segmenting is more expensive to do then logical
the solution we are going for is switches with vlans and dhcp relay agents
at switches so that only broadcast traffic would be dhcp request
it looks simple enough

There is a lot more broadcasts then DHCP queries. The whole infastructure of
how Ethernet itself works is full of different types of broadcasts and other
traffic that have nothing to do with TCP/IP or Windows Networking, like
Route Table Updates with routers, Spanning-Tree Protocol with Switches,
Keep-Alives, and various "Announcements" from every active Host, and plenty
of others I can't list off the top of my head. That is why I always
recommend keeping the number of hosts per segment down below 300.