User Manual
UMN:CLI
V8102
411
The DHCP option format has the following restrictions;
- The value should be within 64 bytes.
- A hidden-length variable should be set once in a single attribute.
- The total length of an option format cannot exceed 254 bytes.
9.6.5.3
Deleting DHCP Option Format
To delete a specified DHCP option format, use the following command.
Command
Mode
Description
no ip dhcp option format NAME
Global
Deletes the given DHCP option format.
9.6.5.4
Displaying DHCP option
To print a specified DHCP option format, use the following command.
Command
Mode
Description
show ip dhcp option format
NAME
[
interface
{
gigabitethernet
|
tengigabitethernet
|
gpon
|
channelgroup
}
IFPORT
vlan
VLANS
]
Enable
Global
DHCP
Option
Prints the given option format and actual raw data in
the packet.
9.6.6
DHCP Option 82
In some networks, it is necessary to use additional information to further determine which
IP addresses to allocate. By using the DHCP option 82, a DHCP relay agent can include
additional information about itself when forwarding client-originated DHCP packets to a
DHCP server. The DHCP relay agent will automatically add the circuit ID and the remote
ID to the option 82 field in the DHCP packets and forward them to the DHCP server.
The DHCP option 82 resolves the following issues in an environment in which untrusted
hosts access the internet via a circuit based public network:
Broadcast Forwarding
The DHCP option 82 allows a DHCP relay agent to reduce unnecessary broadcast flood-
ing by forwarding the normally broadcasted DHCP response only on the circuit indicated
in the circuit ID.
DHCP Address Exhaustion
In general, a DHCP server may be extended to maintain a DHCP lease database with an
IP address, hardware address and remote ID. The DHCP server should implement poli-
cies that restrict the number of IP addresses to be assigned to a single remote ID.
Static Assignment
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