I've got a Cat 6509 running 12.2(16)S IOS. I've configured an ip
helper-address so my VLAN 10 *should* forward DHCP Discover broadcasts
over to my VLAN 11, where I have a DHCP server.

Schematic...
________
DHCP clients --------| |
| | 10.0.11.2
VLAN 10 | 6509 |----- DHCP Svr
| |
DHCP clients --------|________| VLAN 11

10.0.10.x 10.0.11.x

Sniffing VLAN 11 shows me that the DHCP Discovery packets are not
getting across from VLAN 10. Sniffing VLAN 10 also shows that my DHCP
clients-to-be are broadcasting proper DCHP Discover packets.

BTW: DHCP Server *is* working fine. Clients on VLAN 11 get offers back
for their discovery packets. All the Interfaces are up. IP traffic
flows between the VLANs just fine.

Is there something wrong with my configuration? (below) If not, how
would I go about troubleshooting this problem?

!
interface FastEthernet3/13 #example client interface
no ip address
switchport
switchport access vlan 10
switchport mode access
!
interface FastEthernet4/1 #DHCP server's port
no ip address
switchport
switchport access vlan 11
switchport mode access
!
interface Vlan10
ip address 10.0.10.1
ip helper-address 10.0.11.2 #address of DHCP server
!
interface Vlan11
ip address 10.0.11.1
!

Am I missing something?!

Thanks!
--Wulf

Interesting problem. Config seems fine.
1) What are the subnet masks configured on the VLANs (not included in
config, and 10.x.x.x is a class A by default)

2) Can you ping the DHCP server from the switch ? Do you see the MAC
addres of the DHCP server on the switch ? (sh mac-address-table dynamic)

3) The DHCP server , is this a Cisco IOS DHCP Server or a
Microsoft/other DHCP server ??
(I once did tests with a Cisco IOS DHCP server and it seemed that it did
not support unicast forwarded dhcp packets....)

Regards,
Geert

Wulf Losee wrote:

Geert:
Sorry, I hand-typed that config. I'm using /24s on my 10s. It should have read...
Yes, I can ping the server from the other VLANs.

I'm not using MS or Cisco, but DHCP Turbo running on Windoz box.

Anybody know of a debug command that will debug ip helper-address?

Thanks!

Geert <no.spam@nospam.com> wrote in message news:<4088E047.1000101@nospam.com>...

Wulf,

How did you snif on VLAN 11 ?
I hope you mirrored the port of the DHCP server.
DHCP request forwarded with ip helper-address are UNICAST packets,
so they don't get broadcasted out of vlan 11.....

Wulf Losee wrote:

Hi Wulf,

Wulf Losee wrote:
Everything seems fine, however just a check here, are you SURE the
DHCP Server is able to work ACROSS network segments? IE: Is the DHCP
server already in VLAN 11 and only able to work for clients already in
that VLAN? I have seen some people report on DHCP Servers that do not
do this correctly.

Good luck............pk.

Peter <SOMEONE@paradise.net.nz> wrote in message news:<bSBic.3609$cY5.276314@news02.tsnz.net>...
I think the DHCP server needs to be rfc 2132 at minimum and rfc 3046
according to cisco, but 2132 compat should work.

Did you sniff for relay-agent <---> DHCP server unicast packets ?

Rgrds
Rahul Sawarkar

qx49@yahoo.com (Wulf Losee) wrote in message news:<fb7dca7f.0404231242.39aeed8b@posting.google. com>...

The DHCP Turbo is most likely not RFC 3046 complaint.

Rgrds
Rahul Sawarkar