Cisco Systems 3750E Cisco IOS Dhcp Server Database, Dhcp Snooping Binding Database, Release, 22-6

Chapter 22 Configuring DHCP Features and IP Source Guard

Understanding DHCP Features

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 22-3 User-Configured Suboption Packet Formats

Circuit ID Suboption Frame Format (for user-configured string):

Suboption Circuit

type ID type

Length Length

1 N+2	1	N	ASCII Circuit ID string
1 byte 1 byte 1 byte 1 byte			N bytes (N = 3-63)

Remote ID Suboption Frame Format (for user-configured string):

Suboption Remote

type ID type

Length Length

2 N+2	1	N	ASCII Remote ID string or hostname
1 byte 1 byte 1 byte 1 byte			N bytes (N = 1-63)

145774

Cisco IOS DHCP Server Database

During the DHCP-based autoconfiguration process, the designated DHCP server uses the Cisco IOS DHCP server database. It has IP addresses, address bindings, and configuration parameters, such as the boot file.

An address binding is a mapping between an IP address and a MAC address of a host in the Cisco IOS DHCP server database. You can manually assign the client IP address, or the DHCP server can allocate an IP address from a DHCP address pool. For more information about manual and automatic address bindings, see the “Configuring DHCP” chapter of the Cisco IOS IP Configuration Guide,

Release 12.2.

DHCP Snooping Binding Database

When DHCP snooping is enabled, the switch uses the DHCP snooping binding database to store information about untrusted interfaces. The database can have up to 8192 bindings.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

22-6 OL-9775-02