Packets; Values - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BROADBAND ACCESS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

Preventing Option 82 Information from Being Stripped from Trusted Client Packets
Configuring Relay Agent Information Option (Option 82) Suboption Values
Copyright © 2010, Juniper Networks, Inc.
You can configure DHCP relay or DHCP relay proxy to preserve option 82 information for
trusted clients. This ensures that DHCP relay and DHCP relay proxy prevent option 82
information from being stripped off packets destined for a trusted client. A trusted client
has a giaddr value of 0. If DHCP relay is configured not to remove option 82 and the giaddr
field is 0, option 82 information remains in the packets.
To prevent the option 82 information from being removed from packets destined for
a trusted client:
host1(config)#set dhcp relay preserve-trusted-client-option
The DHCP relay agent information option (option 82) enables you to include additional
useful information in the client-originated DHCP packets that the DHCP relay forwards
to a DHCP server.
When the DHCP relay agent information option is enabled, the DHCP relay adds the
option 82 information to packets it receives from clients, then forwards the packets to
the DHCP server. The DHCP server uses the option 82 information to decide which IP
address to assign to the client—the DHCP server might also use information in the option
82 field for additional purposes, such as determining which services to grant to the client.
The DHCP server sends its reply back to the DHCP relay, which removes the option 82
information field from the message, and then forwards the packet to the client.
The option 82 information is made up of a sequence of suboptions. JunosE Software
supports the following DHCP relay agent information suboptions.
Agent Circuit ID (suboption 1)—An ASCII string that identifies the interface on which a
client DHCP packet is received.
Agent Remote ID (suboption 2)—An ASCII string assigned by the relay agent that
securely identifies the client.
Vendor-Specific (suboption 9)—The JunosE Software data field, which contains the
Internet Assigned Numbers Authority (IANA) enterprise number (4874) used by JunosE
Software and either or both the layer 2 circuit ID and the user packet class.
Layer 2 Circuit ID (type 1)—The hexadecimal representation of the layer 2 identifier
in the Agent Circuit ID (suboption 1) value (for example, the ATM VPI/VCI or Ethernet
SVLAN/VLAN ID.) You can configure this suboption type without the Agent Circuit
ID.
User Packet Class (type 2)—The hexadecimal representation of the user packet
class field, whose value is assigned by the layer 2 policy application. The layer 2
policy application can be used to map the DHCP packet or message IEEE 802.1p
value to the user packet class field. See the JunosE Policy Management Configuration
Guide for information about layer 2 policies.
The Agent Circuit ID suboption (suboption 1) and the Agent Remote ID suboption
(suboption 2) are typically determined by the client network access device and depend
Chapter 20: Configuring DHCP Relay
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