DHCP Server not providing service to devices connected to second swit

[rgrisamer]

This network consists of two Catalyst 3750E switches (S1 & S2) which are connected by fiber using 10GB modules. The dhcp server is connected to S1. All devices regardless of the VLAN they belong to that are connected to S1 receive dhcp without issue. No devices connected to S2 can obtain dhcp information, but if I assign a static IP address to one of these devices, they function properly. IP Helper is configured on both switches for all VLANs. Please advise.

[David Ruess]

Hello,

Can you provide the configuration of your switches?

A couple of troubleshooting questions:

1. Is a trunk link configured between the switches?

2. Are both switches allowing the same VLANs on the trunk?

3. Are there any other configurations that could prevent DHCP connectivity such as DHCP snooping?

-David

[rgrisamer]

Hello David and thank you for responding so quickly.

1. Is a trunk link configured between the switches? - Yes

2. Are both switches allowing the same VLANs on the trunk? - I believe so.

3. Are there any other configurations that could prevent DHCP connectivity such as DHCP snooping? Not that I'm aware of.

[MHM Cisco World]

ip default-gateway 10.0.0.254

the default GW not work with IP helper, you need default route toward SW1 (that connect to Server)
MHM 

[David Ruess]

From the looks of your VLAN ACLs it may be preventing the traffic from the DHCP server. You can test a couple of ways.

1. Do a packet capture on the link and check for the 4 DHCP message types (D.O.R.A). If you see all the messages then the problem is likely with SW2 not allowing the packets.

2. You VLAN ACLs don't include entries form the DHCP server back into the VLAN

ip access-list extended DHCP

permit udp host 10.0.0.1 any eq 67 (I believe this is correct syntax)

3. Remove the ACL (or put a permit any any) as the first line and see if the DHCP messages are allowed. If not then I would double check your configuration and connectivity between the switches.

-David

[M02@rt37]

Hello @rgrisamer 

Does a PC on Switch2 with static IP join the DHCP server ?

[rgrisamer · Accepted solution]

Thanks to everyone who responded. I solved the issue. Although S1 had an IP Helper address defined for each VLAN, S2 did not. Once done, it all works as desired.