Dhcp Relay Proxy Overview; Interaction Among Dhcp Relay Proxy, Dhcp Client, And Dhcp Servers - Juniper EX3400 Features Manual

DHCP Relay Proxy Overview

Interaction Among DHCP Relay Proxy, DHCP Client, and DHCP Servers

Copyright © 2017, Juniper Networks, Inc.
DHCP relay proxy mode is an enhancement to extended DHCP relay. DHCP relay proxy
supports all DHCP relay features while providing additional features and benefits.
Normally, extended DHCP relay operates as a helper application for DHCP operations.
Except for the ability to add DHCP relay agent options and the gateway address (giaddr)
to DHCP packets, DHCP relay is transparent to DHCP clients and DHCP servers, and
simply forwards messages between DHCP clients and servers.
When you configure DHCP relay to operate in proxy mode, the relay is no longer
transparent. In proxy mode, DHCP relay conceals DHCP server details from DHCP clients,
which interact with a DHCP relay in proxy mode as though it is the DHCP server. For DHCP
servers there is no change, because proxy mode has no effect on how the DHCP server
interacts with the DHCP relay.
DHCP relay proxy provides the following benefits:
DHCP server isolation and DoS protection—DHCP clients are unable to detect the
DHCP servers, learn DHCP server addresses, or determine the number of servers that
are providing DHCP support. Server isolation also provides denial-of-service (DoS)
protection for the DHCP servers.
Multiple lease offer selection—DHCP relay proxy receives lease offers from multiple
DHCP servers and selects a single offer to send to the DHCP client, thereby reducing
traffic in the network. Currently, the DHCP relay proxy selects the first offer received.
Support for both numbered and unnumbered Ethernet interfaces—For DHCP clients
connected through Ethernet interfaces, when the DHCP client obtains an address, the
DHCP relay proxy adds an access internal host route specifying that interface as the
outbound interface. The route is automatically removed when the lease time expires
or when the client releases the address.
Logical system support—DHCP relay proxy can be configured in a logical system,
whereas a non-proxy mode DHCP relay cannot.
NOTE: You cannot configure both DHCP relay proxy and extended DHCP
local server on the same interface.
The DHCP relay agent is configured on the router (or switch), which operates between
the DHCP client and one or more DHCP servers.
Chapter 4: DHCP Relay Agent
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