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Bronze

service dhcp on C3750

All,

Are the following statements correct:

1) Are "service dhcp" and "ip helper-address" dependent ? I think so. "no service dhcp" will disable the "ip helper-address" functionality. Correct ?

2) Are "service dhcp" and "ip dhcp snooping " dependent ? I don't think so. "no service dhcp" will NOT affect dhcp snooping. Correct ?

regards,

Geert

5 REPLIES
Cisco Employee

Re: service dhcp on C3750

Hello,

"Service DHCP" is used when you configure DHCP server on the switch. You do

not need it for "IP helper-address" configuration. "IP helper-address" is

used in different contexts to convert regular broadcast traffic to directed

unicast.

With regard to DHCP Snooping, again, "Service DHCP" is not a required

command. "Service DHCP" command is used for features that require the switch

to participate in DHCP operations (like DHCP Server, DHCP Relay).

Hope this helps.

Regards,

NT

Bronze

Re: service dhcp on C3750

I'm not sure I agree about the ip helper-address...

On my C4507-Rs, I had "no service dhcp" configured and the "ip helper-address" command would not work.

DHCP broadcasts were NOT being forwarded as unicasts to my DHCP server. As soon as I enabled service dhcp, it started to work as expected.

The 4500s may work differently than the 3750, but that's my experience with it.

HTH

Community Member

Re: service dhcp on C3750

Dear Frieds,

I too faced the same issue that as per the cisco basline configuration no dhcp service can be configured if nor DHCP service is running. But disabling the dhcp service disabled the IP HELPER-ADDRESS fuction as well.  I hope when ip helper address is configured and the router identify the broadcast using the port number 63 and send the unicast to server.

So no dhcp service definitely disables ip helper-address fucction. It happend to me and when I enable dhcp servercie issue went away.

Thanks

K.Satheesh Bsc, PGDIP(Compu.Sc),CCNP R&S

Community Member

service dhcp on C3750

Just to add to the above posts, once i had configured "no service dhcp", just for test purpose (on 6500). Later vlans and SVIs were configured along with helper addresses. However clients were not getting IPs, just then i re enabled "service dhcp" and clients started getting IP addresses.

Regards.

Community Member

Re: service dhcp on C3750

Just resolved incident, where doing " no service dhcp" disrupted only ip phones dhcp services and not PCs. Both PCs and IP phones point to same dhcp server..i.e same "ip helper-address" on voice and data vlan.

IP phones (voice vlan) dhcp packet is on different subnet to DHCP and break, PC(data vlan) dhcp service don't

Sent from Cisco Technical Support iPhone App

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