Enable Dhcp Snooping - 3Com S7906E Configuration Manual

[SwitchB-GigabitEthernet2/0/2] qinq enable
# Apply the uplink policy p2 to the inbound direction of GigabitEthernet 2/0/2.
[SwitchB-GigabitEthernet2/0/2] qos apply policy p2 inbound
# Apply the downlink policy p22 to the outbound direction of GigabitEthernet 2/0/2.
[SwitchB-GigabitEthernet2/0/2] qos apply policy p22 outbound
[SwitchB-GigabitEthernet2/0/2] quit
# Configure GigabitEthernet 2/0/3 to permit frames of the specified SVLANs to pass through.
[SwitchB] interface gigabitethernet 2/0/3
[SwitchB-GigabitEthernet2/0/3] port link-type trunk
[SwitchB-GigabitEthernet2/0/3] port trunk permit vlan 111 211 311 112 212 312
3) Configuration on Switch C
<SwitchC> system-view

# Enable DHCP snooping.

[SwitchC] dhcp-snooping
# Enable ARP detection on each VLAN involved in VLAN mapping.
[SwitchC] vlan 101
[SwitchC-vlan101] arp detection enable
[SwitchC-vlan101] vlan 201
[SwitchC-vlan201] arp detection enable
[SwitchC-vlan201] vlan 301
[SwitchC-vlan301] arp detection enable
[SwitchC-vlan301] vlan 102
[SwitchC-vlan102] arp detection enable
[SwitchC-vlan102] vlan 202
[SwitchC-vlan202] arp detection enable
[SwitchC-vlan202] vlan 302
[SwitchC-vlan302] arp detection enable
[SwitchC-vlan302] vlan 111
[SwitchC-vlan111] arp detection enable
[SwitchC-vlan111] vlan 211
[SwitchC-vlan211] arp detection enable
[SwitchC-vlan211] vlan 311
[SwitchC-vlan311] arp detection enable
[SwitchC-vlan311] vlan 112
[SwitchC-vlan112] arp detection enable
[SwitchC-vlan112] vlan 212
[SwitchC-vlan212] arp detection enable
[SwitchC-vlan212] vlan 312
[SwitchC-vlan312] arp detection enable
[SwitchC-vlan312] vlan 501
[SwitchC-vlan501] arp detection enable
[SwitchC-vlan501] vlan 502
[SwitchC-vlan502] arp detection enable
[SwitchC-vlan502] vlan 503
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