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Community Member

DHCP conflicts

Hi,

I have configured a 3550 switch with 3 vlans. With the following configs

interface Vlan1

description ---> MANAGEMENT VLAN <---

ip address 192.168.10.1 255.255.255.0

ip helper-address 192.168.3.8

!

interface Vlan2

description ---> SERVER VLAN <---

ip address 192.168.3.10 255.255.255.0

ip helper-address 192.168.3.8

!

interface Vlan3

description ---> OFFICE VLAN <---

ip address 192.168.11.1 255.255.255.0

ip helper-address 192.168.3.8

!

For some reasons i am not getting IP address from the DHCP server even after assigning the scope.

Any one have some idea about that why??

Thanks

Rajesh

8 REPLIES
Purple

Re: DHCP conflicts

Rajesh,

What sort of a DHCP server are you using ? And can you ping the DHCP server from the switch ?

Paresh

Community Member

Re: DHCP conflicts

Hi Paresh,

I am using Windows 2003 server. And i can able to ping the server.

I checked the configs. Every thing seems to be fine. But d't know why the system is not getting an ip address.

Apart from creating a DHCP scope on the server is there is any other thing to be configured ???

Thanks

Rajesh

Purple

Re: DHCP conflicts

Rajesh,

Your switch config looks okay. Just one thing, though - you don't need the helper address under interface vlan2 since it is directly connected.

It's gotta be something on your Win2003 server, I'd imagine...

Paresh

Re: DHCP conflicts

Hi Rajesh,

Can you try enabling "spanning-tree portfast" on the ports on which you have connected the client machines which you want to pick an ip address from DHCP server.

Try it and update if it works.

Regards,

Ankur

Community Member

Re: DHCP conflicts

Combined with the ip forward-protocol global configuration command, the ip helper-address command allows you to control which broadcast packets and which protocols are forwarded. Check whether global command ip forward-protocol is there or not.

Community Member

Re: DHCP conflicts

Thanks for your inputs...

Ankur, i didn't use any STP commands at all. In this case how enabling stp at the access ports will help me to forward an IP address.

Rajesh

Re: DHCP conflicts

STP is enabled by default on all ports. DHCP is known to run into problems when access ports has to go through the different states of STP.

Enabling spanning-tree portfast will put the access port directly into forwarding state without having to transition through blocking, listening, learning and forwarding states.

Syntax depends on the type of switch you are using. If you are using an IOS based switch, try 'spanning-tree porfast' on the access ports.

HTH,

Sundar

Purple

Re: DHCP conflicts

Hi Rajesh,

You might want to go through the following document, which highlights a number of potential issues with DHCP and Catalyst switches:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a00800f0804.shtml

Paresh

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