Selecting The Dhcp Server Response; Behavior For Bound Clients And Address Renewals - Juniper JUNOSE SOFTWARE 11.2.X - BROADBAND ACCESS CONFIGURATION GUIDE 7-20-2010 Configuration Manual

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the router does not know when addresses have been renewed or released; the host routes
that are no longer needed are still unavailable.
For additional information on managing client bindings, see "Viewing and Deleting DHCP
Client Bindings" on page 453.

Selecting the DHCP Server Response

Similar to the DHCP relay, the DHCP relay proxy enables you to specify up to five DHCP
servers to provide address and configuration information for a DHCP client. As an added
benefit over the relay, when using multiple DHCP external servers, you can configure how
the DHCP relay proxy determines which offer to send to the DHCP client. You can configure
the DHCP relay proxy to use either the single best offer or the first offer it receives from
the DHCP servers.
If there are multiple offers, the DHCP relay proxy selects the final offer based on the
following priorities:
The offer that contains the IP address requested by the DHCP client.
1.
The offer that contains an IP address on the same subnetwork as the requested IP
2.
address.
The offer that has the longest lease time.
3.
If you have enabled the optional select-first-offer feature, the DHCP relay proxy
immediately uses the first offer that it receives from any DHCP server.

Behavior for Bound Clients and Address Renewals

When a DHCP client is already bound to an IP address or is renewing the lease on its IP
address, DHCP relay proxy unicasts DHCP ACK and DHCP NAK replies to the client
regardless of the current configuration of the set dhcp relay layer2-unicast-replies
command or the set dhcp relay broadcast-flag-replies command. These commands
control the transmission method used for DHCP reply packets.
This behavior applies only to DHCP relay proxy; it does not apply to DHCP relay because
DHCP relay does not maintain a list of active clients or receive address renewal requests
from clients.
For information about using the set dhcp relay layer2-unicast-replies command, see
"Configuring Layer 2 Unicast Transmission Method for Reply Packets to DHCP Clients"
on page 490. For information about using the set dhcp relay broadcast-flag-replies
command, see "Configuring Layer 2 Unicast Transmission Method for Reply Packets to
DHCP Clients" on page 490.
Managing Host Routes on page 508
set dhcp relay proxy
set dhcp relay proxy send-first-offer
set dhcp relay proxy timeout
Chapter 20: Configuring DHCP Relay
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