Preventing Dhcp Relay From Installing Host Routes By Default; Configuration Example Preventing Installation Of Host Routes - Juniper JUNOSE 11.1.X - BROADBAND ACCESS CONFIGURATION GUIDE 6-4-2010 Configuration Manual

JUNOSe 11.1.x Broadband Access Configuration Guide
Table 101: Router Configuration and Transmission of DHCP Reply Packets (continued)

Preventing DHCP Relay from Installing Host Routes by Default

The Address Resolution Protocol (ARP) performs spoof checking on all incoming ARP
requests by default. For each incoming packet, ARP does a route lookup on the source
IP address to determine the interface on which that IP address was routed. ARP then
verifies that the interface on which the packet was received matches the routed
interface. If the interface on which the packet was received does not match the routed
interface, the router drops the packet.
When you configure applications such as DHCP relay that automatically install routes,
you must ensure that the routes are correctly installed for your configuration. DHCP
relay installs host routes by default, which is required in certain configurations to
enable address renewals from the DHCP server to work properly. However, the
default installation of host routes might cause a conflict when you configure DHCP
relay with static subscriber interfaces. To avoid these configuration conflicts, use the
set dhcp relay inhibit-access-route-creation command to prevent DHCP relay from
installing host routes by default. The command enforces consistent state of the route
and client database.
In relay mode, this command removes all installed host routes from IP, deletes all
host routes from mirrored storage and NVS, and stops accumulating host route
information.
In relay proxy mode, this command removes all installed host routes from IP, deletes
all NVS client data, and stops installing host routes for newly bound clients in IP.
However, it does preserve the client data in mirrored storage and continues
preservation of newly bound clients in mirrored storage.
The no set dhcp relay inhibit-access-route-creation command enforces consistent
state of the route and client database. In relay proxy mode, after the unified ISSU is
completed and normal operations resume, this command installs a host route for all
existing bound clients in IP and saves it in NVS.
Configuration Example—Preventing Installation of Host Routes
This example describes a sample procedure for configuring multiple subscribers over
a particular static subscriber interface (ip53001 in this example) you might use
500
Configuring DHCP Relay and BOOTP Relay
Broadcast Flag Layer 2 Unicast
Replies Replies
Disabled (off) Disabled (off)
Router Behavior if Router Behavior if
Broadcast Flag Set Broadcast Flag Not Set
DHCP relay and DHCP DHCP relay and DHCP relay
relay proxy broadcast proxy broadcast DHCP
DHCP reply packets to reply packets to clients. For
clients. For information information about
about exceptions to this exceptions to this behavior
behavior for DHCP relay for DHCP relay proxy, see
proxy, see "Behavior for "Behavior for Bound Clients
Bound Clients and Address and Address Renewals" on
Renewals" on page 520 . page 520 .