3Com Router 3000 Ethernet FamilyConfiguration Guide Chapter 9 DHCP Configuration3Com Corporation9-7z If the RADIUS server of the specified domain is unreachable for some reason, theDHCP server sends up to three DHCP accounting start requests (including the firstsending attempt) at regular intervals. If the three start requests bring no responsefrom the RADIUS server, the DHCP server does not send start requests any more.9.2.4 Option 82 Support on the DHCP ServerOption 82 is a relay agent information option in the DHCP packet. When a requestpacket from a DHCP client travels through a DHCP relay on its way to the DHCP server,the DHCP relay inserts the option 82 field into the request packet. Option 82 includesmany sub-options, but the DHCP server supports only sub-option 5 at present. Whenthe DHCP relay adds the IP address of a segment into sub-option 5 of option 82, theDHCP server can assign an IP address or the configuration information according tooption 82.I. Basic concepts for option 821) OptionsOptions is a length-variable field in the DHCP packet for carrying information such aspart of the lease information and packet type. It can include up to 255 options and mustcomprise at least one option.2) Option 82Option 82, also known as relay agent information option, is a part of the Options field ofDHCP packet. According to RFC3046, option 82 lies before option 255 and after theother options. Option 82 can include up to 255 sub-options and must comprise at leastone sub-option. Up to now, the frequently used sub-options in option 82 are sub-option1, sub-option 2, and sub-option 5.3) Sub-option 1As a sub-option of option 82, sub-option 1 represents the agent circuit ID, namelyCircuit ID. It holds the VLAN-ID and MAC address of the switch port for the DHCP client,which usually you must configure on the DHCP relay.Generally, sub-option 1 and sub-option 2 must be used in conjunction to identifyinformation about the DHCP source end.4) Sub-option 2Sub-option 2 is also a sub-option of option 82 and represents the remote agent ID,namely Remote ID. It holds the MAC address of the DHCP relay, which usually youmust configure on the DHCP relay.Generally, sub-option 1 and sub-option 2 must be used in conjunction to identifyinformation about the DHCP source end.5) Sub-option 5
