Default Client/Server Interaction; Dynamic Client/Server Interaction For Dhcpv4; Dynamic Configuration Options - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

Default Client/Server Interaction

Dynamic Client/Server Interaction for DHCPv4

Dynamic Configuration Options

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Typically the DHCP client initiates all of the basic DHCP client/server interactions. The
DHCP server sends information to a client only in response to a request from that client.
In subscriber management scenarios, this behavior does not enable a client to be quickly
updated with its network address and configuration in the event of server changes.
For example, suppose a service provider restructured its addressing scheme or changed
the server IP addresses that it provided to clients. Without dynamic reconfiguration, the
service provider typically clears the DHCP server binding table, but cannot inform the
DHCP clients that their bindings have been cleared. Consequently, the DHCP client
operates as though its IP address is still valid, but it is now unable to communicate over
the access network, resulting in an outage. The DHCP local server has to wait for the
client to send a message to renew its lease or rebind to the server. In response, the server
sends a NAK message to the client to force it to begin the DHCP connection process
again. Alternatively, the provider can wait for customers to make a service call about the
network failures and then instruct them to power cycle their customer premises equipment
to reinitiate the connection. Neither of these actions is timely or convenient for customers.
Dynamic reconfiguration for DHCPv4 is available through a partial implementation of
RFC 3203, DHCP Reconfigure Extension for DHCPv4. It enables the DHCPv4 local server
to send a message to the client to force reconfiguration.
The server sends a forcerenew message to a DHCPv4 client, initiating a message
exchange. In response, DHCPv4 clients that support the forcerenew message then send
a lease renewal message to the server. The server rejects the lease renewal request and
sends a NAK to the client, causing the client to reinitiate the DHCP connection. A
successful reconnection results in the reconfiguration of the DHCP client. Only the
exchange of forcerenew, renew, and NAK messages is supported from RFC 3202.
When the local server state machine starts the reconfiguration process on a bound client,
the client transitions to the reconfiguring state and the local server sends a forcerenew
message to the client. Because the client was in the bound state before entering the
reconfiguring state, all subscriber services, such as forwarding and statistics, continue
to work. Client statistics are not maintained in the interval between a successful
reconfiguration and the subsequent client binding. When the server responds to the client
renewal request with a NAK, the client entry is removed from the binding table and final
statistics are reported. New statistics are collected when the client sends a discover
message to establish a new session.
You can enable dynamic reconfiguration for all DHCP clients or only the DHCP clients
serviced by a specified group of interfaces, and you can modify the behavior accordingly.
To enable dynamic reconfiguration with default reconfiguration values for all DHCP
clients, include the reconfigure
hierarchy level for DHCPv4 clients. In a routing instance, include the
statement at the [edit system services dhcp-local-server]
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reconfigure