ZyXEL Communications OLT2406 - Dhcpv4 Relay; Dhcpv4 Relay Agent Information

Chapter 42 DHCP
OLT2406 User’s Guide
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42.3 DHCPv4 Relay
Configure DHCP relay on the OLT if the DHCP clients and the DHCP server are not in the same broadcast
domain. During the initial IP address leasing, the OLT helps to relay network information (such as the IP
address and subnet mask) between a DHCP client and a DHCP server. Once the DHCP client obtains an
IP address and can connect to the network, network information renewal is done between the DHCP
client and the DHCP server without the help of the OLT.
The OLT can be configured as a global DHCP relay. This means that the OLT forwards all DHCP requests
from all domains to the same DHCP server. You can also configure the OLT to relay DHCP information
based on the VLAN membership of the DHCP clients.
42.3.1 DHCPv4 Relay Agent Information
The OLT can add information about the source of client DHCP requests that it relays to a DHCP server by
adding Relay Agent Information. This helps provide authentication about the source of the requests. The
DHCP server can then provide an IP address based on this information. Please refer to RFC 3046 for more
details.
The DHCP Relay Agent Information feature adds an Agent Information field (also known as the Option
82 field) to DHCP requests. The Option 82 field is in the DHCP headers of client DHCP request frames that
the OLT relays to a DHCP server.
42.3.1.1 DHCPv4 Relay Agent Information Format
A DHCP Relay Agent Information option has the following format.
i1, i2 and iN are DHCP relay agent sub-options, which contain additional information about the DHCP
client. You need to define at least one sub-option.
42.3.1.2 Sub-Option Format
There are two types of sub-option: “Agent Circuit ID Sub-option” and “Agent Remote ID Sub-option”.
They have the following formats.
The 1 in the first field identifies this as an Agent Circuit ID sub-option and 2 identifies this as an Agent
Remote ID sub-option. The next field specifies the length of the field.
Table 154 DHCP Relay Agent Information Option Format
Code
(82)
Length
(N)
i1 i2
...
iN
Table 155 DHCP Relay Agent Circuit ID Sub-option Format
SubOpt Code Length Value
1
(1 byte)
N
(1 byte)
String
Table 156 DHCP Relay Agent Remote ID Sub-option Format
SubOpt Code Length Value
2
(1 byte)
N
(1 byte)
String