2-3Figure 2-2 Configure trusted ports in a cascaded networkTable 2-1 describes roles of the ports shown in Figure 2-2.Table 2-1 Roles of portsDevice Untrusted port Trusted port disabled fromrecording binding entriesTrusted port enabled torecord binding entriesSwitch A GigabitEthernet 1/0/1 GigabitEthernet 1/0/3 GigabitEthernet 1/0/2Switch BGigabitEthernet 1/0/3and GigabitEthernet1/0/4GigabitEthernet 1/0/1 GigabitEthernet 1/0/2Switch C GigabitEthernet 1/0/1 GigabitEthernet 1/0/3 andGigabitEthernet 1/0/4 GigabitEthernet 1/0/2DHCP Snooping Support for Option 82Option 82 records the location information of the DHCP client. The administrator can locate the DHCPclient to further implement security control and accounting.If DHCP snooping supports Option 82, it will handle a client’s request according to the contents definedin 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 theOption 82 before forwarding the reply to the client. If the reply contains no Option 82, the DHCPsnooping device forwards it directly.If a client’srequestingmessage has…HandlingstrategyPaddingformat The DHCP snooping device will…Drop Random Drop the message.Option 82Keep Random Forward the message without changingOption 82.
