DHCP problems

MrXpert

I labbed a network (rented virtual via proctor labs) consisting of 4 Multi layer switches (3550), 4 routers (IP routing disabled and acting like hosts) and a DHCP server (R6)

I configured SVIS on all the MLS and setup OSPF advertising the 172.16.x.y/24 networks and the 46.46.46.0/24 between SW4 and R6. Please note I neglected to show the 46.46.46.0/24 network between CAT4 and R6 in the picture. CAT4 has the ip address 46.46.46.4/24 on its fast ethernet interface connected to R6. R6 is...you guessed it 46.46.46.6

see pic here https://www.mediafire.com/?yy12k9c0ai74u5w

There was full reachability between all switches and DHCP server, sourcing from the various SVIs.

I then configured a DHCP pool on R6 so that it read

ip dhcp pool VLAN10
default-router 172.16.10.1
network 172.16.10.0 /24

ip dhcp pool VLAN20
default-router 172.16.20.3
network 172.16.20.0 /24

ip dhcp pool VLAN30
default-router 172.16.30.2
network 172.16.30.0 /24

ip dhcp pool VLAN40
default-router 172.16.40.2
network 172.16.40.0 /24

ip excluded-address 172.16.10.1 172.16.10.5
ip excluded-address 172.16.20.1 172.16.20.5
ip excluded-address 172.16.30.1 172.16.30.5
ip excluded-address 172.16.40.1 172.16.40.5

I applied the ip address dhcp command on the hosts and unshut the interface. However the hosts did not pick up a IP address from dhcp server so i then typed ip helper-address 46.46.46.6 on all the SVIS of the switches.
I ran debug ip dhcp server packet on R6 but although it appeared to be receiving dhcp packets I could not determine why it was not leasing any out
The funny thing is, is that I have done this same lab many many times with success but today (after a switching break of a few months) i could not get it working. My own conclusion is that there is something amiss with my configuration of ip helper-address?

any ideas?

EdTheLad

If i understand you correctly, you have ospf running between SW4 and R6 only, with this setup you would configure SW4 with the ip helper address, if you want to have the helper address on the SVI of switches SW1,SW2 and SW3, those switches would need to participate in ospf to learn the dest network 46.46.46.0/24.

MrXpert

EdTheLad wrote: »

If i understand you correctly, you have ospf running between SW4 and R6 only, with this setup you would configure SW4 with the ip helper address, if you want to have the helper address on the SVI of switches SW1,SW2 and SW3, those switches would need to participate in ospf to learn the dest network 46.46.46.0/24.

As mentioned

"There was full reachability between all switches and DHCP server, sourcing from the various SVIs"

In other words SW1, SW2, SW3, SW4 and R6 are all running OSPF. There is full reachability. So SW1,SW2, SW3,SW4 can currently ping R6 sourcing it from ANY of their SVIs.

I already had ip helper address 46.46.46.6 on all the SVIs belonging to SW1,SW2,SW3 and SW4. Not sure why it is not working. I assumed i'd misused the ip helper address command?

EdTheLad

Is DHCP snooping enabled on the switches? Remove ip helper from SW4. Other that that provide all configs!

Dieg0M

Have you checked if you have any DHCP conflicts? sh ip dhcp conflict