
SNMP, RMON, BootP, DHCP, and RARP Concepts
117362-A Rev. A 2-35
6. The router receives the packet and forwards it to all servers.
7. Those servers examine the packet, and if their IP addresses differ from the
value in the server IP address field, they reclaim the IP addresses they
supplied in the DHCPOFFER packets. These addresses are now available for
other clients.
8. The target server recognizes its IP address in the server IP address field, and
responds to the DHCPREQUEST packet as follows:
• If the target server can supply the requested configuration parameters, it
sends a DHCPACK packet to the client through the BootP relay agent.
The client examines the configuration parameters in the DHCPACK
packet and records the duration of the lease period. If the client detects a
problem with the configuration parameters, it sends a DHCPDECLINE
packet to the server and issues a new DHCPDISCOVER packet.
Otherwise, the client accepts the configuration parameters.
• If the target server cannot supply the requested configuration parameters,
it sends a DHCPNAK packet to the client through the BootP relay agent.
When the client receives the DHCPNAK packet, it broadcasts a new
DHCPDISCOVER packet and the process begins again.
A client may choose to relinquish its IP address before the lease period
expires by sending a DHCPRELEASE packet to the server. This packet
contains the relinquished IP address in the client IP address field and the
client’s MAC address in the client hardware address field.
Acquiring the Same IP Address Again
A client may want to reuse an IP address that a server allocated earlier by DHCP.
In this case, the interchange between client and server omits some of the steps
described in the previous section, and proceeds as follows:
1. The client starts the interchange by broadcasting a DHCPREQUEST packet
that contains its previous IP address in the client IP address field.
2. The BootP relay agent forwards the packet to DHCP servers on other
networks.
3. DHCP servers examine the client’s configuration parameters in the options
field of the DHCPREQUEST packet.
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