3com 5500-ei pwr Installation Instruction

 

3-3 

Figure 3-2 Padding contents for sub-option 1 of Option 82 

 

 

Figure 3-3 Padding contents for sub-option 2 of Option 82 

 

 

The procedure for a DHCP client to obtain an IP address from a DHCP server through a DHCP relay 

agent is similar to that for the client to obtain an IP address from a DHCP server directly. The following 

are the mechanism of Option 82 support on DHCP relay agent. 

1)  Upon receiving a DHCP request, the DHCP relay agent checks whether the packet contains Option 

82 and processes the packet accordingly. 

z 

If the request packet contains Option 82, the DHCP relay agent processes the packet depending 

on the configured strategy (that is, discards the packet, replaces the original Option 82 in the 

packet with its own, or leaves the original Option 82 unchanged in the packet), and forwards the 

packet (if not discarded) to the DHCP server. 

z 

If the request packet does not contain Option 82, the DHCP relay agent adds Option 82 to the 

packet and forwards the packet to the DHCP server. 

2)  Upon receiving the packet returned from the DHCP server, the DHCP relay agent strips Option 82 

from the packet and forwards the packet with the DHCP configuration information to the DHCP 

client. 

 

Request packets sent by a DHCP client fall into two categories: DHCP-DISCOVER packets and 

DHCP-REQUEST packets. As DHCP servers coming from different manufacturers process DHCP 

request packets in different ways (that is, some DHCP servers process Option 82 in DHCP-DISCOVER 

packets, whereas the rest process Option 82 in DHCP-REQUEST packets), a DHCP relay agent adds 

Option 82 to both types of packets to accommodate to DHCP servers of different manufacturers.