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New Member

DHCP on different network segments

Hi,

I am trying to run DHCP on VLAN on another network segment, than the DHCP server is. The VLAN is routed on c4503, network with DHCP server is routed on c7206VXR. Catalyst and router are connected by 802.1q trunk (L3 connection is realized through VLAN 1000). Network with DHCP server is on other router?s interface than c4503. I set "ip helper-address" on interface Vlan on c4503, also set "ip forwarding-protocols udp" on c4503. It didn?t work, so I set ip helper and forwarding of udp also on router subinterface ge 0/1.1000 (which is used for L3 connection to catalyst). But it seems, that DHCP broadcasts still don?t make it to the router.

Topology in the attachement...

Any suggestions?

Thanks a lot, Martin

5 REPLIES
Cisco Employee

Re: DHCP on different network segments

Hi Martin,

Can you ping your DHCP server from your layer 3 switch using source ip address as your interface vlan 213? Just want to make sure your oute to DHCP server from layer 3 switch is available or not.

Regards,

Ankur

New Member

Re: DHCP on different network segments

Hi Ankur,

yes, of course I can, there is no problem with IP connectivity at all.

Martin

Cisco Employee

Re: DHCP on different network segments

Hi Martin,

If IP connectivity is fine then is it possible for your to sniff the ports on way to the DHCP server to find if the DHCP request is trasvering or not to the DHCP server.

Your broadcast should reach your layer 3 switch and from there it should be a normal unicast packet.

Regards,

Ankur

Re: DHCP on different network segments

Hi Martin,

Can you try below:

1. Connect PC on the same segment in which DHCP server resides and see if PC is getting IP from server. Just to isolate if inter-vlan routing is a problem.

2. Reserve one IP on server and configure it manually on PC and see if PC can ping gateway and other resources. If PC is able to ping, then there is a problem during DHCP process.

3. Check inter-vlan routing on c4503 and c7206.

4. if you see ip-helper address command on interface vlan on c4503, you dont need to set "ip forward-protocols udp", if ur objective is just to obtain IP from DHCP.

Try this out ... hope it helps...

New Member

Re: DHCP on different network segments

Thanks for all replies,

it was actually my mistake - there was "no service dhcp" set on c4503 (probably something from old configuration) :)

Sorry for bothering... have a nice weekend.

Martin

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