CLI Reference Guide-R01

Chapter 9 | General Security Measures
DHCPv4 Snooping
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This example enables the DHCP Snooping Information Option.
Console(config)#ip dhcp snooping information option
Console(config)#
ip dhcp snooping
information option
encode no-subtype
This command disables the use of sub-type and sub-length fields for the
circuit-ID (CID) and remote-ID (RID) in Option 82 information generated by the
switch. Use the no form to enable the use of these fields.
Syntax
[no] ip dhcp snooping information option encode no-subtype
Default Setting
CID/RID sub-type: Enabled
Command Mode
Global Configuration
Command Usage
◆ Option 82 information generated by the switch is based on TR-101 syntax as
shown below:
The circuit identifier used by this switch starts at sub-option1 and goes to the
end of the R-124 string. The R-124 string includes the following information:
■
sub-type - Distinguishes different types of circuit IDs.
■
sub-length - Length of the circuit ID type
■
access node identifier - ASCII string. Default is the MAC address of the
switch’s CPU. This field is set by the ip dhcp snooping information option
command,
■
eth - The second field is the fixed string “eth”
■
slot - The slot represents the stack unit for this system.
■
port - The port which received the DHCP request. If the packet arrives over
a trunk, the value is the ifIndex of the trunk.
■
vlan - Tag of the VLAN which received the DHCP request.
Note that the sub-type and sub-length fields can be enabled or disabled
using the ip dhcp snooping information option command.
Table 60: Option 82 information
82 3-69 1 1-67 x1 x2 x3 x4 x5 x63
opt82 opt-len sub-opt1 string-len R-124 string