Cisco Catalyst 4500 Series - Configuring DHCP Snooping

53-6
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
OL_28731-01
Chapter 53 Configuring DHCP Snooping, IP Source Guard, and IPSG for Static Hosts
Configuring DHCP Snooping
Figure 53-3 shows the packet formats for user-configured remote ID and circuit ID suboptions. The
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:
• 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.
Figure 53-3 User-Configured Suboption Packet Formats
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:
• Default Configuration for DHCP Snooping, page 53-7
• Enabling DHCP Snooping, page 53-7
Length Length
Circuit
ID type
Suboption
type
Circuit ID Suboption Frame Format (for user-configured string):
Remote ID Suboption Frame Format (for user-configured string):
Suboption
type
Length Length
Remote
ID type
145774
N1N+2 1
N1N+2 2
ASCII Circuit ID string
1 byte 1 byte 1 byte N bytes (N = 3-63)
ASCII Remote ID string or hostname
N bytes (N = 1-63)
1 byte
1 byte 1 byte 1 byte1 byte