12.2.9 When a DHCP relay that assigns Option82 to the Switch is connected

When you connect a DHCP relay under the Switch and the DHCP relay adds its data in the Option 82 field of the DHCP packets received from the DHCP client, configure the Switch so it can forward the packets.

The following figure shows an example configuration when a DHCP relay that adds Option 82 data is connected under the Switch.

Figure 12-13: Example configuration when DHCP relays are connected to which Option82 are assigned to the Switch

DHCP snooping settings for the Switch are the same as those in 12.2.2 Basic Settings, 12.2.4 Terminal Filtering, and 12.2.5 Dynamic ARP Checking.

In the example here, the DHCP packets and IPv4 packets from the DHCP client cannot be relayed. In addition, the ARP packets from the Layer 3 switch/router cannot be relayed.

To relay the packets, you need to permit the forwarding of DHCP packets, IPv4 packets, and ARP packets on the Switch. When the DHCP relay adds Option 82 data, you also need to permit the forwarding of DHCP packets with Option 82 data.

<Structure of this section>

(1) Setting to allow forwarding of DHCP packets

The configuration for permitting the forwarding of IPv4 packets is the same as the configuration when a DHCP relay is connected under the Switch.

For details about the settings, see 12.2.8 When DHCP relays are connected under the Switch (1) Allow forwarding of DHCP packets.

(2) Setting to allow forwarding of IPv4 packets

The configuration for permitting the forwarding of IPv4 packets is the same as the configuration when a DHCP relay is connected under the Switch.

For details about the settings, see 12.2.8 When DHCP relays are connected under the Switch (2) Allow forwarding of IPv4 packets.

(3) Setting to allow forwarding of ARP packets

The configuration for permitting the forwarding of ARP packets is the same as the configuration when a terminal with a fixed IP address is connected.

For details about the settings, see 12.2.7 When a terminal with a fixed IP is connected.

(4) Setting to allow forwarding of DHCP packets with Option82

Points to note: Disable the Option 82 spoofing check for DHCP packets.

Command examples

(config)# ip dhcp snooping information option allow-untrusted

Disables the Option 82 spoofing check for the DHCP packets received on the untrusted port.