Configuring Dhcp Snooping Entries Backup - HP A5120 EI Series Configuration Manual

To do...
Configure user-
defined Option
82
NOTE:

You can configure DHCP snooping to support Option 82 on Layer 2 Ethernet interfaces and Layer 2 aggregate
interfaces only.

If a Layer 2 Ethernet interface is added to an aggregation group, enabling DHCP snooping to support Option
82 on the interface will not take effect. After the interface quits the aggregation group, the configuration will be
effective.

To support Option 82, perform related configuration on both the DHCP server and the switch enabled with
DHCP snooping. For DHCP server configuration of this kind, see the chapter ―DHCP server configuration‖.

If the handling strategy of the DHCP-snooping-enabled device is configured as replace, you must configure a
padding format for Option 82. If the handling strategy is keep or drop, you need not configure any padding
format.

If the Option 82 is padded with the device name (sysname) of a node, the device name must contain no spaces.
Otherwise, the DHCP-snooping-enabled device will drop the message. You can use the sysname command to
specify the device name. For more information about this command, see Device management commands in the
Fundamentals Command Reference

If DHCP snooping and QinQ work together or the DHCP snooping switch receives a DHCP packet with two
VLAN tags, and the normal or verbose padding format is adopted for Option 82, DHCP snooping fills the
VLAN ID field of sub-option 1 with outer VLAN tag.inter VLAN tag. For example, if the outer VLAN tag is 10 (a
in hexadecimal) and the inner VLAN tag is 20 (14 in hexadecimal), the VLAN ID is 000a.0014.

Configuring DHCP snooping entries backup

DHCP snooping entries cannot survive a reboot. If the DHCP snooping switch is rebooted, security
modules (such as IP source guard) that use DHCP snooping entries to authenticate users will reject
requests from clients until new entries are learned.
The DHCP snooping entries backup feature enables you to store DHCP snooping entries in a file. When
the DHCP snooping switch reboots, it reads DHCP snooping entries from this file.
Follow these steps to configure DHCP snooping entries backup
To do...
Enter system view
Use the command...
Configure the
padding content dhcp-snooping information [ vlan vlan-id
for the circuit ID ] circuit-id string circuit-id
sub-option
Configure the
dhcp-snooping information [ vlan vlan-id
padding content
] remote-id string { remote-id | sysname
for the remote ID
}
sub-option
.
Use the command...
system-view
Remarks
—
70
Remarks
Optional
By default, the
padding content
depends on the
padding format of
Option 82.
Optional
By default, the
padding content
depends on the
padding format of
Option 82.