Option 18 for DHCPv6 snooping

Option 18, also called the interface-ID option, is used by the DHCPv6 relay agent to determine the interface to use to forward RELAY-REPLY message.

The DHCPv6 snooping device adds Option 18 to the received DHCPv6 request message before forwarding it to the DHCPv6 server. The server then assigns IP address to the client based on the client information in Option 18.

Figure 82 shows the Option 18 format, which includes the following fields:

• Option code—Option code.

• Option length—Size of the option data.

• Port index—Port that receives the DHCPv6 request from the client.

• VLAN ID—ID of the outer VLAN.

• Second VLAN ID—ID of the inner VLAN.

• DUID—DUID of the DHCPv6 client.

	NOTE: The Second VLAN ID field is optional. If the received DHCPv6 request does not contain a second VLAN, Option 18 also does not contain it.