Configuring Advanced Threat Protection

DHCP Snooping

N o t e

N o t e

DHCP snooping only overrides the Option 82 settings on a VLAN that has snooping enabled, not on VLANS without snooping enabled.

If DHCP snooping is enabled on a switch where an edge switch is also using DHCP snooping, it is desirable to have the packets forwarded so the DHCP bindings are learned. To configure the policy for DHCP packets from untrusted ports that already have Option 82 present, enter this command in the global configuration context.

Syntax: [no] dhcp-snooping option 82 [remote-id <mac subnet-ip mgmt-ip>] [untrusted-policy <drop keep replace>]

Enables DHCP Option 82 insertion in the packet.

remote-idSet the value used for the remote-idfield of the relay information option.

mac: The switch mac address is used for the remote-id. This is the default.

subnet-ip:The IP address of the VLAN the packet was received on is used for the remote-id. If subnet-ipis specified but the value is not set, the MAC address is used.

mgmt-ip:The management VLAN IP address is used as the remote-id. If mgmt-ipis specified but the value is not set, the MAC address is used.

untrusted- Configures DHCP snooping behavior when

policy forwarding a DHCP packet from an untrusted port that already contains DHCP relay information (Option 82). The default is drop.

drop: The packet is dropped.

keep: The packet is forwarded without replacing the option information.

replace: The existing option is replaced with a new Option 82 generated by the switch.

The default drop policy should remain in effect if there are any untrusted nodes, such as clients, directly connected to this switch.

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