VTP + Spanning Tree DHCP

[lecarbajalp]

Hello,

I have an issue connecting 2 switch's, my core its a 3750X ( 2 switch's connected like a stack)  and the access is a 2960S

( 2 switch's connected like a stack) , i create port channels , each physical port from the access network its connected to a different switch ( core switch) in order to have some redundancy, the vtp master its the 3750X and the vtp client its the 2960S , it got the information correctly related to the Vlans i also configured a MST tree instance in the core sw 3750X ( instance 1 -2 ) in my access switch is onnly configured a instance 0 , the issue is that i can not get a IP from the DHCP configured for the vlan of user in the access switch's.

Thank you

Regards

,

[smehrnia]

Hi Luis,

that's because the Client's DHCP request broadcasts cant reach the DHCP server, i'm sure thats Bcoz of ur vlan structure. you need to configure ip helper-address command on your SVI's (L3 vlan interfaces).

Hope it Helps,
plz Rate helpful posts.

Soroush.

[lecarbajalp]

Hello,

thank you for answer, my dhcp is configured in my core Sw 3750X not in a server.

Any ideas why it can not be reached?

[smehrnia]

DHCP requests are broadcast and can not get out of a VLAN scope all by themselvs, you have to pass them to DHCP server (whether its a router, switch or a pc... doesnt matter), through a dhcp relay agent. what's ur connection from Access to 3750... trunk?

have u tried to move the DHCP server config from 3750 to 2960?

Soroush.

[lecarbajalp]

Hello, I only configured the dhcp for an specific VLAN it wont across to another, about the port its configured like a trunk ,do i need to also include this command in the port channel of my core sw 3750X and in the 2960S ?

switchport trunk allow vlan all

Regards,

[smehrnia]

the trunk should allow traffic for that vlan to pass and also you need to have a VLAN interface for that particular vlan on ur 3750 with proper ip address on it, if it still doesnt work, it doesnt hurt to set ip helper-address on the VLAN interface on 3750 n see if it gets it right.

HTH,

Soroush.

[nkarthikeyan]

Hi Luis,

For the uplink interfaces you have to make the ip dhcp snooping trust..... If u have any restrictions you nmay not get the IP's from the DHCP..... Please check and let me know the same.