dhcp only offers IP for one subnet

  • Thread starter Thread starter Terry G
  • Start date Start date
T

Terry G

Our current setup:
Edge router with static entries, OSPF and RIP are off, proxy-arp is
on.
--------------
Fiber runs
Router - has 10+ fiber F-------------- Switches serving PCs.
lines running from F--------------
individual gig ports F--------------
to switches throughout F--------------
building.
DHCP server connected
to FE ports on blades Cat 5 -------- DHCP server
in router.
-------------------

DHCP is set to one huge scope x.x.10.1 through x.x.18.255, mask
255.255.0.0
Exclusions are set to allow the following addresses to be offered
x.x.10.1-126
x.x.11.1-126
x.x.13.1-190
x.x.14.1-190
x.x.16.126-190
x.x.18.1-126

DHCP server is on the 13.1-190 range.
It has the SwitchedNetworkFlags reghack set to give out the same IP
adress as the PC address and router gateway address.
This currently works and gives out IPs just fine.
--
What we are trying to do:
We want to get rid of Proxy arp which means we have to lose the
SwitchedNetworkFlag.
I set up a superscope with appropriate subnetting as below:
x.x.10.1-126 255.192
x.x.11.1-126 255.192
x.x.13.1-190 255.128
x.x.14.1-190 255.128
x.x.16.126-190 255.192
x.x.18.65-126 255.192

We have entries for appropriate gateways for each range.

The problem: The DHCP server only gives out addresses for the
53.1-126 range.

TG
 
Terry G said:
I set up a superscope with appropriate subnetting as below:
x.x.10.1-126 255.192
x.x.11.1-126 255.192
x.x.13.1-190 255.128
x.x.14.1-190 255.128
x.x.16.126-190 255.192
x.x.18.65-126 255.192
The problem: The DHCP server only gives out addresses for the
53.1-126 range.
Click to expand...

Superscopes take all the addresses in all the child scopes and make them
behave as on huge scope for one huge subnet. The solution is,...don't use
Superscopes. Use a separate scope for each subnet and set the router that is
between the subnets to forward DHCP request to the proper DHCP Server and
all will be well. The router supplies information in the request it forwards
so the DHCP server knows which subnet the request came from and grant a
proper address for the proper subnet.

I was fooled by the Superscope concept myself and also did it wrong the
first time.

Make sure the reghack is corrected.
 
Phillip Windell said:
Superscopes take all the addresses in all the child scopes and make them
behave as on huge scope for one huge subnet. The solution is,...don't use
Superscopes. Use a separate scope for each subnet and set the router that is
between the subnets to forward DHCP request to the proper DHCP Server and
all will be well. The router supplies information in the request it forwards
so the DHCP server knows which subnet the request came from and grant a
proper address for the proper subnet.

I was fooled by the Superscope concept myself and also did it wrong the
first time.

Make sure the reghack is corrected.
Click to expand...

I just tried it with no change. Scopes removed from superscope,
superscope deleted, ip helper-address set on the router (tried it as
forwarded to server address and to all interfaces), reghack appears to
have been removed when I set the specific gateways. Server does not
appear to make any offers. In past half hour server stats shows 70+
discovers, 0 offers, 5 requests, 0 acks, 1 nack, 2 declines, 0
releases. Addresses are available, but not in 13.x range. When I put
the current production dhcp on and have helper-address on router
pointed to the new (problem) dhcp server, the new makes no offers and
the production still hands out an IP address.
 
Terry G said:
I just tried it with no change. Scopes removed from superscope,
superscope deleted, ip helper-address set on the router (tried it as
forwarded to server address and to all interfaces), reghack appears to
have been removed when I set the specific gateways. Server does not
appear to make any offers. In past half hour server stats shows 70+
discovers, 0 offers, 5 requests, 0 acks, 1 nack, 2 declines, 0
releases. Addresses are available, but not in 13.x range. When I put
the current production dhcp on and have helper-address on router
pointed to the new (problem) dhcp server, the new makes no offers and
the production still hands out an IP address.
Click to expand...

I don't know what to make of the ongoing problem, but I am confident that
you do not need Superscopes. Has the machine been rebooted or at least had
the DHCP service stopped and started since the "reghack" was removed? I
really don't know what else to make of it other than remove and reinstall
the DHCP service, or worse yet reload the machine from scrarch,...I am
always sceptical of "reg hacks" of that nature and their possible ongoing
lingering effects.
 
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