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New Member

DHCP relay problem CAT3750X


Have recently installed a 4 switch Cat3750X stack for a Customer.

The stack is acting as distribution switch and server aggregation in their enterprise LAN.

Routing  is enabled on the stack and there are a few diffrent VLAN's (server,  client, print, wireless clients). A centralized DHCP server is placed on  the server VLAN and the plan was to use IP Helper/DHCP relay on the  client VLAN's.

But - the DHCP service is not working and I suspect some problem with the IP Helper funtionality on the 3750X stack.

The scenario is:

- The client send a DCHP broadcast

- The broadcast is received by the 3750 switch on the local interface with IP Helper enabled

- The switch sends a DHCP unicast to the server

- The server replies to the switch

... so far so good ..

- But the switch never sends the DHCP reply back to the client as a broadcast ....

Have attached an output from the DHCP debug on the 3750 where I can see f.ex:

Jun 19 12:00:31.490: DHCPD: Sending notification of ASSIGNMENT_FAILURE:

Jun 19 12:00:31.490:  DHCPD: due to: CANT FORWARD

... so temporary we have to use the switch as a DHCP server (which is not wanted by the customer).

Some details:

- Have attached config for the stack

- Are using IOS 15.0.1-SE2 with IP base licence

Everyone's tags (2)
New Member

DHCP relay problem CAT3750X


just did a quick read on your attachment,

from the config i can see that you only configure the ip helper address on vlan 201.

but the debug shows that even for the client on vlan 201 the switch cant forward the DHCP OFFER,

where are the client of 201 connected to?


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