Dhcp Relay; Chapter 26 Dhcp Relay; Dhcp Relay Agent Information Option (Option 82); Private Format - ZyXEL Communications SAM1316-22 User Manual

C
H A P T E R
This chapter shows you how to set up DHCP relays for each VLAN.

26.1 DHCP Relay

DHCP (Dynamic Host Configuration Protocol, RFC 2131 and RFC 2132) allows
individual clients to obtain TCP/IP configuration at start-up from a DHCP server.
You can configure the SAM1316-22 to relay DHCP requests to one or more DHCP
servers and the server's responses back to the clients. You can specify default
DHCP servers for all VLAN, and you can specify DHCP servers for each VLAN.
26.2 DHCP Relay Agent Information Option
(Option 82)
The SAM1316-22 can add information to DHCP requests that it relays to a DHCP
server. This helps provide authentication about the source of the requests. You can
also specify additional information for the SAM1316-22 to add to the DHCP
requests that it relays to the DHCP server. Please see RFC 3046 for more details.

26.2.1 Private Format

The DHCP relay agent information feature adds an Agent Information field to the
option 82 field of the DHCP headers of DHCP request frames that the SAM1316-22
relays to a DHCP server. The Agent Information field that the SAM1316-22 adds
contains an "Agent Circuit-ID sub-option" that includes the slot and port numbers,
VLAN ID and optional information about the slot and port on which the DHCP
request was received.
The following table shows the format of the private Agent Circuit ID sub-option.
The (binary) "1" in the first field identifies this as an Agent Circuit ID sub-option.
The length N gives the total number of octets in the Agent Information Field. If
the configuration request was received on a DSL port, a 1-byte Slot No field
SAM1316-22 User's Guide
26

DHCP Relay

183