Set A Timeout For Dhcp Client Renewal Messages; Managing Host Routes - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BROADBAND ACCESS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

JunosE 11.3.x Broadband Access Configuration Guide

Set a Timeout for DHCP Client Renewal Messages

Managing Host Routes

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the most appropriate offer it receives from the configured DHCP servers to the DHCP
client.
host1(config)#set dhcp relay proxy send-first-offer
You can set the amount of time, in the range 1–168 hours, that the DHCP relay proxy
waits for a renewal message from DHCP clients after a router reboot or switchover occurs.
A renewal message is required from DHCP clients when a router reboot or switchover
occurs. If no renewal message is received before the timeout expires, the relay proxy
declares the client no longer active and removes the client's host route By default, DHCP
relay proxy uses timeout of 72 hours.
host1(config)#set dhcp relay proxy timeout 8
NOTE: DHCP relay proxy does not remove a DHCP client's host route when
the lease for the client's IP address expires. DHCP relay proxy will instead
remove the host route when the relay proxy timeout expires. To prevent a
host route from remaining long after lease expiration, modify the relay proxy
timeout from its default setting of 72 hours to a setting close to, but not less
than the lease time.
The DHCP relay proxy feature enables the E Series router to efficiently manage host
routes for DHCP clients, including:
Installing routes when DHCP clients are configured
Removing routes when DHCP clients release their DHCP-assigned addresses or when
the addresses expire
When a DHCP client sends a request to an external DHCP server, the relay proxy receives
the request and forwards it to the external DHCP server. The relay proxy then sends the
DHCP server's response back to the client. This process is similar to that used by the
DHCP relay component. The DHCP client views the relay proxy as a DHCP server, and
the DHCP server sees the relay proxy as a DHCP relay agent.
To DHCP clients, there is no difference when they use a DHCP relay or a DHCP relay proxy.
However, the DHCP relay proxy differs from the DHCP relay in how client address renewals
and releases are handled:
With the DHCP relay proxy, DHCP clients communicate with the relay proxy to renew
and release addresses.
With the DHCP relay, DHCP clients communicate directly with the DHCP server to
renew and release addresses.
A major benefit of the relay proxy configuration is that the E Series router is kept informed
of the status of a DHCP client's address. When addresses are released by clients, the
router removes the installed host route for that client. In the DHCP relay configuration,
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