Solved: DHCP not working as expected.

jstewart33 · ‎11-12-2008

I have an 1841 at a branch location configured to hand out IPs via DHCP on the router. I only want to hand out about a hundred and thirty addresses on of the default class C network. So the problem is that after about a month of running the current index is showing 117 which to me is strange since there are only about 40 machines in this location. I also set the lease to 6 days so I would have figured not to see such a high index. I'm sure this is something simple that I'm overlooking, but I'm not sure of what it is. I will attach the current config to help with troubleshooting. Thanks for the time.

Giuseppe Larosa · ‎11-12-2008

Hello Jerrod,

I see the same on one of my remote branh routers

RT-TGR-AQUILA#sh ip dhcp pool

Pool LAN :

Utilization mark (high/low) : 100 / 0

Subnet size (first/next) : 0 / 0

Total addresses : 14

Leased addresses : 3

Pending event : none

1 subnet is currently in the pool :

Current index IP address range Leased addresses

10.34.26.55 10.34.26.49 - 10.34.26.62 3

RT-TGR-AQUILA#

RT-TGR-AQUILA#sh run | inc dhcp

no ip dhcp use vrf connected

ip dhcp excluded-address 10.34.26.49

ip dhcp excluded-address 10.34.26.52

ip dhcp excluded-address 10.34.26.51

ip dhcp excluded-address 10.34.26.60

ip dhcp pool LAN

RT-TGR-AQUILA#

the number that appears in sh ip dhcp pool looks like to be not aware of excluded addresses but simply comes from subnet mask.

Hope to help

Giuseppe

View solution in original post

Giuseppe Larosa · ‎11-12-2008

Hello Jerrod,

I don't see anything wrong there are only 40 entries in the show ip dhcp binding as the number of real machines.

the server allocates ip addresses from the pool but there is no constraint to assign ip addresses contigously.

This happens also on Cisco Network Registrar.

Hope to help

Giuseppe

jstewart33 · ‎11-12-2008

Ok that makes sense. When I look at my pool information though it makes me a little nervous since it says 254 total addresses. So does the ip dhcp excluded-address, keep the pool from handing out the range of addresses that I don't want DHCP to touch? Thank you for your quick response.

Giuseppe Larosa · ‎11-12-2008

Hello Jerrod,

I see the same on one of my remote branh routers

RT-TGR-AQUILA#sh ip dhcp pool

Pool LAN :

Utilization mark (high/low) : 100 / 0

Subnet size (first/next) : 0 / 0

Total addresses : 14

Leased addresses : 3

Pending event : none

1 subnet is currently in the pool :

Current index IP address range Leased addresses

10.34.26.55 10.34.26.49 - 10.34.26.62 3

RT-TGR-AQUILA#

RT-TGR-AQUILA#sh run | inc dhcp

no ip dhcp use vrf connected

ip dhcp excluded-address 10.34.26.49

ip dhcp excluded-address 10.34.26.52

ip dhcp excluded-address 10.34.26.51

ip dhcp excluded-address 10.34.26.60

ip dhcp pool LAN

RT-TGR-AQUILA#

the number that appears in sh ip dhcp pool looks like to be not aware of excluded addresses but simply comes from subnet mask.

Hope to help

Giuseppe