ZyXEL Communications XGS-4526 User Manual

Chapter 41 DHCP

XGS-4526/4528F/4728F User’s Guide

Configure DHCP relay on the Switch if the DHCP clients and the DHCP server are 
not in the same broadcast domain. During the initial IP address leasing, the 
Switch 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 Switch.

The Switch can be configured as a global DHCP relay. This means that the Switch 
forwards all DHCP requests from all domains to the same DHCP server. You can 
also configure the Switch to relay DHCP information based on the VLAN 
membership of the DHCP clients.

The Switch 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 to 
the Option 82 field. The Option 82 field is in the DHCP headers of client DHCP 
request frames that the Switch relays to a DHCP server.

Relay Agent Information can include the System Name of the Switch if you 
select this option. You can change the System Name in Basic Settings > 
General Setup. 

The following describes the DHCP relay information that the Switch sends to the 
DHCP server:

Table 132   Relay Agent Information

Slot ID

(1 byte) This value is always 0 for stand-alone switches.

Port ID

(1 byte) This is the port that the DHCP client is connected to.

VLAN ID

(2 bytes) This is the VLAN that the port belongs to.

Information

(up to 64 bytes) This optional, read-only field is set according to 
system name set in Basic Settings > General Setup.