Configuring Dhcp Snooping - Cisco Catalyst 4500 series Administration Manual

Configuring DHCP Snooping

Figure 53-3
switch uses these packet formats when DHCP snooping is globally enabled and when the ip dhcp
snooping information option format remote-id global configuration command and the ip dhcp
snooping vlan information option format-type circuit-id string interface configuration command are
entered.
The values for these fields in the packets change from the default values when you configure the remote
ID and circuit ID suboptions:
•
•
Figure 53-3
Circuit ID Suboption Frame Format (for user-configured string):
Suboption
type
1 byte
Remote ID Suboption Frame Format (for user-configured string):
Suboption
type
1 byte
Configuring DHCP Snooping
When you configure DHCP snooping on your switch, you are enabling the switch to differentiate
untrusted interfaces from trusted interfaces. You must enable DHCP snooping globally before you can
use DHCP snooping on a VLAN. You can enable DHCP snooping independently from other DHCP
features.
These sections describe how to configure DHCP snooping:
•
•
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
53-6
shows the packet formats for user-configured remote ID and circuit ID suboptions. The
Circuit ID suboption fields
The circuit ID type is 1.
–
The length values are variable, depending on the length of the string that you configure.
–
Remote ID suboption fields
The remote ID type is 1.
–
The length values are variable, depending on the length of the string that you configure.
–
User-Configured Suboption Packet Formats
Circuit
ID type
Length Length
1 N+2 1 N ASCII Circuit ID string
1 byte 1 byte 1 byte
Remote
ID type
Length Length
2 N+2 1 N
ASCII Remote ID string or hostname
1 byte 1 byte 1 byte
Default Configuration for DHCP Snooping, page 53-7
Enabling DHCP Snooping, page 53-7
Chapter 53 Configuring DHCP Snooping, IP Source Guard, and IPSG for Static Hosts
N bytes (N = 3-63)
N bytes (N = 1-63)
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