3Com S7906E - Switch, Configuration Manual

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5-3
To save system resources, you can disable the trusted ports, which are indirectly connected to DHCP
clients, from recording clients’ IP-to-MAC bindings upon receiving DHCP requests.
Figure 5-2 Configure trusted ports in a cascaded network
Table 5-1 describes roles of the ports shown in Figure 5-2 .
Table 5-1 Roles of ports
Device Untrusted port
Trusted port disabled from
recording binding entries
Trusted port enabled to
record binding entries
Switch A GigabitEthernet2/0/1 GigabitEthernet2/0/3 GigabitEthernet2/0/2
Switch B
GigabitEthernet2/0/3 and
GigabitEthernet2/0/4
GigabitEthernet2/0/1 GigabitEthernet2/0/2
Switch C GigabitEthernet2/0/1
GigabitEthernet2/0/3 and
GigabitEthernet2/0/4
GigabitEthernet2/0/2
DHCP Snooping Support for Option 82
Option 82 records the location information of the DHCP client. The administrator can locate the DHCP
client to further implement security control and accounting. For more information, refer to Relay agent
option (Option 82) .
If DHCP snooping supports Option 82, it will handle a client’s request according to the contents defined
in Option 82, if any. The handling strategies are described in the table below.
If a reply returned by the DHCP server contains Option 82, the DHCP snooping device will remove the
Option 82 before forwarding the reply to the client. If the reply contains no Option 82, the DHCP
snooping device forwards it directly.