I N I T I A L C O N F I G U R A T I O N A N D B A C K G R O U N D I N F O R M A T I O N
Rev H
36 of 244
automatic reuse of an address that is no longer needed by the client to which it was
assigned. Thus, dynamic allocation is particularly useful for assigning an address to a
client that will be connected to the network only temporarily or for sharing a limited pool
of IP addresses among a group of clients that do not need permanent IP addresses.
Dynamic allocation may also be a good choice for assigning an IP address to a new client
being permanently connected to a network where IP addresses are scarce and it is
important to reclaim them when old clients are retired.
•
Manual allocation
- a client's IP address is assigned by the network administrator, and
DHCP is used simply to convey the assigned address to the client. A particular network
will use one or more of these mechanisms, depending on the policies of the network
administrator. Manual allocation allows DHCP to be used to eliminate the error-prone
process of manually configuring hosts with IP addresses in environments where (for
whatever reasons) it is desirable to manage IP address assignment outside of the DHCP
mechanisms.
As shown in
, the parameter negotiation starts with a DHCPDISCOVER broadcast
message from the client seeking a DHCP Server. The DHCP Server responds with a
DHCPOFFER unicast message offering configuration parameters (such as an IP address, a
MAC address, a domain name, and a lease for the IP address) to the client. The client returns a
DHCPREQUEST broadcast message requesting the offered IP address from the DHCP Server.
The DHCP Server responds with a DHCPACK unicast message confirming that the IP address
has been allocated to the client.
Figure 4-1 Obtaining an IP Address from a DHCP Server
The client may suggest values for the IP address and lease time in the DHCPDISCOVER
message. The client may include the
requested IP address
option to suggest that a particular IP
address be assigned, and may include the
IP address lease time
option to suggest the lease
time it would like to have. The
requested IP address
option is to be filled in only in a
DHCPREQUEST message when the client is verifying network parameters obtained
previously.
If a server receives a DHCPREQUEST message with an invalid
requested IP address
, the
server should respond to the client with a DHCPNAK message and may choose to report the
problem to the system administrator. The server may include an error message in the
message
option.
Summary of Contents for AC - 232 - TX
Page 4: ......
Page 24: ......
Page 44: ......
Page 50: ......
Page 68: ......
Page 79: ...C L I C O M M A N D M O D E S Rev H 79 of 244 Figure 9 4 Network Mode show and set Commands ...
Page 81: ...C L I C O M M A N D M O D E S Rev H 81 of 244 Figure 9 8 SIP Mode show and set Commands ...
Page 98: ......
Page 108: ......
Page 156: ......
Page 158: ......
Page 170: ......
Page 184: ......
Page 202: ......
Page 228: ......
Page 234: ......
Page 242: ......