3Com 2928 User Guide - Page 324
DHCP Snooping Support for Option 82, DHCP Snooping Configuration Task List
UPC - 662705557113
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Table 3-1 Roles of ports Device Untrusted port Switch A Switch B GigabitEthernet 1/0/1 GigabitEthernet 1/0/3 and GigabitEthernet 1/0/4 Switch C GigabitEthernet 1/0/1 Trusted port disabled from Trusted port enabled to recording binding entries record binding entries GigabitEthernet 1/0/3 GigabitEthernet 1/0/2 GigabitEthernet 1/0/1 GigabitEthernet 1/0/2 GigabitEthernet 1/0/3 and GigabitEthernet 1/0/4 GigabitEthernet 1/0/2 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 Introduction to 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. If a client's requesting message has... Handling strategy The DHCP snooping device will... Drop Drop the message. Option 82 Keep Replace Forward the message without changing Option 82. Forward the message after replacing the original Option 82 with the Option 82 padded in normal format. no Option 82 - Forward the message after adding the Option 82 padded in normal format. DHCP Snooping Configuration Task List Complete the following tasks to configure DHCP snooping: Task Remarks Enabling DHCP Snooping Required By default, DHCP snooping is disabled. Configuring DHCP Snooping Functions on an Interface Required Specify an interface as trusted and configure DHCP snooping to support Option 82. By default, an interface is untrusted and DHCP snooping does not support Option 82. You need to specify the ports connected to the authorized DHCP servers as trusted to ensure that DHCP clients can obtain valid IP addresses. The trusted port and the port connected to the DHCP client must be in the same VLAN. 3-3