DHCP is out of IPs in Class C network

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J

Jay

My network has grown to the point that my DHCP server in
my class C network always run out of IP addresses for
some clients. What is the best way to solve this problem?
I am using network address translation, thanks.
 
Jay said:
My network has grown to the point that my DHCP server in
my class C network always run out of IP addresses for
some clients. What is the best way to solve this problem?
I am using network address translation, thanks.
Click to expand...

NAT is not even relative to the subject. The question I guess, is how much
are you willing to do? You could knock a bit or two off the network side of
the Subnet Mask but then you may eventually run into overcrowding of hosts
on a single logical segment. There can be effieciency problems when you
start getting near 250-300 hosts.

You could add another address block to the system to create another logical
segment, but that requires buying a LAN router or a high-end switch that has
built in routing functions, and it may require a little topology
redesigning.
 
You could re-create the scope as a class B, reconfigure any static address
machines, etc. But, Phill is right, if you are already approaching 250
machines on this network, it's probably time to create a second subnet. You
need a router, or you could use a 2 adpater windows machine.

Doug Sherman
MCSE Win2k/NT4.0, MCSA, MCP+I, MVP
 
This is a bit of a complicated question that is hard to answer
well without more information.

Generally, the "best" way usually is to open up your network mask
and add another DHCP range in the new address area(s) created.

For example: if you are now using, say, 192.168.1.* with
a 24-bit network mask of 255.255.255.0 (254 addresses),
you can change your network mask to 23-bits (255.255.254.0).
This opens up 192.168.0.* for LAN use and gives you 510
useable addresses. (192.168.0.1 through 192.168.1.254)
You can then add a second scope to DHCP to give out
addresses in this new range.

The catch in the above of course is that you have to convert
every device on your network to the new addressing. This
is sometimes not so simple. You can do it in two stages: first
distribute the wider network mask through DHCP and
manual assignment as required, and then when that is done
implement the new addresses.

If your default gateway router can handle multiple static LAN network
routes you may be able to program it to route between these two
"networks" during the time you are transitioning. (This is
sometimes termed a "router-on-a-stick" BTW since all the
traffic being routed is actually coming in and going out on
the same LAN segment.)

If your site is larger, the above will not be simple at all, and may not
even be a choice. In that case you have to add another LAN network
and implement some sort of segmentation and routing topology to
connect them. You can do this in a server with multiple NICs and
RRAS, but in this case I strongly advise using a separate routing box
(or boxes) to avoid a lot of headaches.

Steve Duff, MCSE, MVP
Ergodic Systems, Inc.
 
The idea of renumbering the network to a class B is the
one that appears easy for me. I anticipate at the most
260 to 270 hosts. Does this pose a problem for one
network? Please let me know what I might be missing and
the problems that I'm likely to encounter, thanks.


-----Original Message-----
My network has grown to the point that my DHCP server in
my class C network always run out of IP addresses for
some clients. What is the best way to solve this problem?
I am using network address translation, thanks.
Click to expand...

NAT is not even relative to the subject. The question I guess, is how much
are you willing to do? You could knock a bit or two off the network side of
the Subnet Mask but then you may eventually run into overcrowding of hosts
on a single logical segment. There can be effieciency problems when you
start getting near 250-300 hosts.

You could add another address block to the system to create another logical
segment, but that requires buying a LAN router or a high- end switch that has
built in routing functions, and it may require a little topology
redesigning.

--

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


.
Click to expand...
 
Jay said:
The idea of renumbering the network to a class B is the
one that appears easy for me. I anticipate at the most
260 to 270 hosts. Does this pose a problem for one
network? Please let me know what I might be missing and
the problems that I'm likely to encounter, thanks.
Click to expand...

It would work. But at 260-270 host you may start to experience traffic
problems since you aren't segmenting.
 
Steve, I'm now seriously considering your suggestion
below. My network is not that big and I'm now using
192.168.1.0/24 so this might work but I want to be sure
of the steps.
1). Change the subnet masks of all hosts with static IPs
to 255.255.254.0
2). In DCHP create a new scope for 192.168.0.1 to
192.168.0.254 since I already have 192.168.1.1 to
192.168.1.254.
3). I'm not very sure of the routing part - can you pls.
shed some light here or direct me to where I can get some
help, thanks.




-----Original Message-----
This is a bit of a complicated question that is hard to answer
well without more information.

Generally, the "best" way usually is to open up your network mask
and add another DHCP range in the new address area(s) created.

For example: if you are now using, say, 192.168.1.* with
a 24-bit network mask of 255.255.255.0 (254 addresses),
you can change your network mask to 23-bits (255.255.254.0).
This opens up 192.168.0.* for LAN use and gives you 510
useable addresses. (192.168.0.1 through 192.168.1.254)
You can then add a second scope to DHCP to give out
addresses in this new range.

The catch in the above of course is that you have to convert
every device on your network to the new addressing. This
is sometimes not so simple. You can do it in two stages: first
distribute the wider network mask through DHCP and
manual assignment as required, and then when that is done
implement the new addresses.

If your default gateway router can handle multiple static LAN network
routes you may be able to program it to route between these two
"networks" during the time you are transitioning. (This is
sometimes termed a "router-on-a-stick" BTW since all the
traffic being routed is actually coming in and going out on
the same LAN segment.)

If your site is larger, the above will not be simple at all, and may not
even be a choice. In that case you have to add another LAN network
and implement some sort of segmentation and routing topology to
connect them. You can do this in a server with multiple NICs and
RRAS, but in this case I strongly advise using a separate routing box
(or boxes) to avoid a lot of headaches.

Steve Duff, MCSE, MVP
Ergodic Systems, Inc.

"Jay" <[email protected]> wrote in
Click to expand...
message news:[email protected]...
 
Jay said:
Steve, I'm now seriously considering your suggestion
below. My network is not that big and I'm now using
192.168.1.0/24 so this might work but I want to be sure
of the steps.
1). Change the subnet masks of all hosts with static IPs
to 255.255.254.0
2). In DCHP create a new scope for 192.168.0.1 to
192.168.0.254 since I already have 192.168.1.1 to
192.168.1.254.
Click to expand...

No. No new scopes, just change the mask in the existing scope. You have to
delete and recreate the scope to do that.

3). I'm not very sure of the routing part - can you pls.
shed some light here or direct me to where I can get some
help, thanks.
Click to expand...

There is no routing,...it as all still one subnet,...that is what the mask
does,..it broadens the IP# Range of the subnet.
 
Phillip, thanks for clarifying this but how do I
reconcile this with Steve's contribution above. I just
want to make sure I do it right the first time.
The 2 steps below is all I need to do?
-----Original Message-----



No. No new scopes, just change the mask in the existing scope. You have to
delete and recreate the scope to do that.

3). I'm not very sure of the routing part - can you pls.

There is no routing,...it as all still one
Click to expand...
subnet,...that is what the mask
does,..it broadens the IP# Range of the subnet.

--

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


.
Click to expand...
 
I thnk he was giving you more than one option and you might be confusing two
different ones together.

Changing the mask from 255.255.255.0 to 255.255.254.0 simply gives the same
subnet a larger range of addresses, that is all it does. You just have to
make sure that all hosts (computers, switches, hubs, routers, ..everything)
has their mask replaced with the new mask. Changing the DHCP Scope will
take care of all the "automatic" hosts, but you have to do all the static
ones yourself manually.

The new mask will make the old network ID 192.168.0.0 go from the old range
of:
192.168.0.0 -- 192.168.0.255 (254 usable hosts [256 minus 2])
up to the new range of:
192.168.0.0 -- 192.168.1.255 (510 usable hosts [512 minus 2])

--

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


Jay said:
Phillip, thanks for clarifying this but how do I
reconcile this with Steve's contribution above. I just
want to make sure I do it right the first time.
The 2 steps below is all I need to do?
-----Original Message-----



No. No new scopes, just change the mask in the existing scope. You have to
delete and recreate the scope to do that.

3). I'm not very sure of the routing part - can you pls.

There is no routing,...it as all still one
Click to expand...
subnet,...that is what the mask
does,..it broadens the IP# Range of the subnet.

--

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


.
Click to expand...
Click to expand...
 
Well-said Phillip - Though you mean "The new mask will
make the old network ID 192.168.1.0 go from the old range
of:
192.168.1.0 -- 192.168.1.255 (254 usable hosts [256
minus 2])
up to the new range of:
192.168.0.0 -- 192.168.1.255 (510 usable hosts [512
minus 2])", right?


-----Original Message-----
I thnk he was giving you more than one option and you might be confusing two
different ones together.

Changing the mask from 255.255.255.0 to 255.255.254.0 simply gives the same
subnet a larger range of addresses, that is all it does. You just have to
make sure that all hosts (computers, switches, hubs, routers, ..everything)
has their mask replaced with the new mask. Changing the DHCP Scope will
take care of all the "automatic" hosts, but you have to do all the static
ones yourself manually.

The new mask will make the old network ID 192.168.0.0 go from the old range
of:
192.168.0.0 -- 192.168.0.255 (254 usable hosts [256 minus 2])
up to the new range of:
192.168.0.0 -- 192.168.1.255 (510 usable hosts [512 minus 2])

--

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


Phillip, thanks for clarifying this but how do I
reconcile this with Steve's contribution above. I just
want to make sure I do it right the first time.
The 2 steps below is all I need to do?
-----Original Message-----

Steve, I'm now seriously considering your suggestion
below. My network is not that big and I'm now using
192.168.1.0/24 so this might work but I want to be sure
of the steps.
1). Change the subnet masks of all hosts with static IPs
to 255.255.254.0
2). In DCHP create a new scope for 192.168.0.1 to
192.168.0.254 since I already have 192.168.1.1 to
192.168.1.254.

No. No new scopes, just change the mask in the
Click to expand...
existing
scope. You have to
delete and recreate the scope to do that.

3). I'm not very sure of the routing part - can you pls.
shed some light here or direct me to where I can get some
help, thanks.

There is no routing,...it as all still one
Click to expand...
subnet,...that is what the mask
does,..it broadens the IP# Range of the subnet.

--

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


.
Click to expand...
Click to expand...


.
Click to expand...
 
Jay said:
Well-said Phillip - Though you mean "The new mask will
make the old network ID 192.168.1.0 go from the old range
of:
192.168.1.0 -- 192.168.1.255 (254 usable hosts [256
minus 2])
up to the new range of:
192.168.0.0 -- 192.168.1.255 (510 usable hosts [512
minus 2])", right?
Click to expand...

I meant it just as I wrote it. The Id of 192.168.1.0 would no longer exist,
so I began with the ID that still exists in either mask, which is "0", so
the comparison is more accurate. With the new mask the possible IDs are 0, 2
,4 ,8, etc., if I am not in error. But anyway the new range is:
192.168.0.0 -- 192.168.1.255 (510 usable hosts [512 minus 2])
 
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