Absent for while from the forums.
Back with DHCP Relay issue.
I'll try to keep this explanation as brief as possible.
Sophos acting as router-on-stick with two separate physical interfaces.
1. Eth1 -> HP1810 Switch
2. Eth2 -> Cisco 3560 Switch
Eth1 is a trunk on the HP switch, trunking 5 VLANs to a vSphere environment.
VLAN1; VLAN10; VLAN20; VLAN30; VLAN 50.
On VLAN10 there is a Windows 2012 DHCP server, with scopes for the rest of the VLANs.
All VLAN interfaces are listed as DHCP Relay agents on the Sophos and clients on those VLANs are obtaining DHCP leases successfully.
No additional config on the HP1810 was necessary.
But here's where the good story ends.
Eth3 is a trunk on the Cisco 3560 switch.
It is supposed to be trunking 2 VLANs from customer premise, 2010 Data VLAN and 2020 Voice VLAN.
Both the Data and Voice VLAN clients should be able to obtain leases from the Windows 2012 DHCP server mentioned previously.
Both VLAN interfaces, 2010 and 2020 are listed as DHCP Relays on the Sophos.
The ip-helper is configured for the VLAN interfaces on the Cisco 3560 pointing to the Windows DHCP server.
The Windows DHCP server is configured with the necessary scopes.
Even DHCP snooping has been enabled on the Cisco 3560, and the trunk interface connecting to the Sophos has been ip dhcp snooping trust enabled.
There is IP connectivity and the Cisco 3560 can ping the Windows DHCP and vice versa.
If static IPs are setup on the clients everything works.
No dynamic leases can be obtained however.
If Sophos is configured for DHCP server everything works fine, however the Windows server is considered as a requirement for DHCP.
The only thing I haven't configured is the OSPF routing between the Eth1 and Eth 3, but that is due to the fact that they are already being routed as indicated before....
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