INS_CNGE3FE8MS[POE][HO] Rev. 11.7.17 PAGE 36
INSTRUCTION MANUAL CNGE3FE8MS[POE][HO]
TECH SUPPORT: 1.888.678.9427
DHCP Relay
A DHCP relay agent is used to forward and to transfer DHCP messages between the clients
and the server when they are not in the same subnet domain. It stores the incoming interface
IP address in the GIADDR field of the DHCP packet. The DHCP server can use the value of
GIADDR field to determine the assigned subnet. For such condition, please make sure the switch
configuration of VLAN interface IP address and PVID (Port VLAN ID) correctly.
Object Description
Relay Mode Indicates the DHCP relay mode operation. Possible modes are:
Enabled: Enable DHCP relay mode operation. When DHCP relay mode operation is enabled, the
agent forwards and transfers DHCP messages between the clients and the server when they are
not in the same subnet domain. And the DHCP broadcast message won’t be flooded for security
considerations.
Disabled: Disable DHCP relay mode operation.
Relay Server Indicates the DHCP relay server IP address.
Relay
Information
Mode
Indicates the DHCP relay information mode option operation. The option 82 circuit ID format as
“[vlan_id][module_id][port_no]”. The first four characters represent the VLAN ID, the fifth and sixth
characters are the module ID (in standalone device it always equal 0, in stackable device it means
switch ID), and the last two characters are the port number. For example, “00030108” means the
DHCP message receives form VLAN ID 3, switch ID 1, port No 8. And the option 82 remote ID value
is equal the switch MAC address.
Possible modes are:
Enabled: Enable DHCP relay information mode operation. When DHCP relay information mode
operation is enabled, the agent inserts specific information (option 82) into a DHCP message when
forwarding to DHCP server and removes it from a DHCP message when transferring to DHCP client.
It only works when DHCP relay operation mode is enabled.
Disabled: Disable DHCP relay information mode operation.
Relay
Information
Policy
Indicates the DHCP relay information option policy. When DHCP relay information mode operation
is enabled, if the agent receives a DHCP message that already contains relay agent information it will
enforce the policy. The ‘Replace’ policy is invalid when relay information mode is disabled. Possible
policies are:
Keep: Keep the original relay information when a DHCP message that already contains it is received.
Apply Click to apply changes.
Reset Click to revert to previous values.
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