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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter22 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.
Figure22-3 User-Configured Suboption Packet Formats
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 ho st 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 snoopi ng binding database to store
information about untrusted interfaces. The database can have up to 8192 bindings.
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