Digisol DG-FS4528P, Руководство по управлению

Страница: 90 / 973

C
HAPTER
4 | Basic Management Tasks
Setting the Switch’s IP Address
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DHCP request packets are flooded onto the VLAN which received the
request if DHCP relay service is enabled on the switch, and the request
packet contains a valid (i.e., non-zero) relay agent address field.
DHCP reply packets received by the relay agent are handled as follows:
1.
When the relay agent receives a DHCP reply packet with Option 82
information on the management VLAN, it first ensures that the
packet is destined for it, and then removes the Option 82 field from
the packet.
2. If the DHCP packet’s broadcast flag is on, the switch uses the
circuit-id information contained in the option 82 information fields
to identify the VLAN connected to the requesting client and then
broadcasts the DHCP reply packet to this VLAN. If the DHCP
packet’s broadcast flag is off, the switch uses the circuit-id
information in option 82 fields to identify the interface connected to
the requesting client and unicasts the reply packet to the client
DHCP reply packets are flooded onto the VLAN which received the reply
if DHCP relay service is enabled and any of the following situations
apply:
The reply packet does not contain Option 82 information.
The reply packet contains a valid relay agent address field (that is
not the address of this switch), or receives a reply packet with a
zero relay agent address through the management VLAN.
The reply packet is received on a non-management VLAN.
DHCP Relay Option 82 Policy – Specifies how to handle DHCP client
request packets which already contain Option 82 information:
Drop – Floods the request packet onto the VLAN that received the
original request instead of relaying it.
Keep – Retains the Option 82 information in the client request,
inserts the relay agent’s address, and unicasts the packet to the
DHCP server.
When the Option 82 policy is set to “keep” the original information
in the request packet, the frame type specified by the ip dhcp relay
information option command is ignored.
Replace – Replaces the Option 82 information circuit-id and
remote-id fields in the client’s request with information provided by
the relay agent itself, inserts the relay agent’s address, and unicasts
the packet to the DHCP server. (This is the default policy.)