Cisco Ios Dhcp Server Database; Dhcp Snooping Binding Database - Cisco Catalyst 3560-X Software Configuration Manual

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Table of Contents

Understanding DHCP Features

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

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

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

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 12.4.

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 64,000 bindings.

Each database entry (binding) has an IP address, an associated MAC address, the lease time (in

hexadecimal format), the interface to which the binding applies, and the VLAN to which the interface

belongs. The database agent stores the bindings in a file at a configured location. At the end of each entry

is a checksum that accounts for all the bytes from the start of the file through all the bytes associated

with the entry. Each entry is 72 bytes, followed by a space and then the checksum value.

To keep the bindings when the switch reloads, you must use the DHCP snooping database agent. If the

agent is disabled, dynamic ARP inspection or IP source guard is enabled, and the DHCP snooping

binding database has dynamic bindings, the switch loses its connectivity. If the agent is disabled and only

DHCP snooping is enabled, the switch does not lose its connectivity, but DHCP snooping might not

prevent DHCP spoofing attacks.

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

User-Configured Suboption Packet Formats

ASCII Circuit ID string

1 byte 1 byte 1 byte

ASCII Remote ID string or hostname

1 byte 1 byte 1 byte

Configuring DHCP Features and IP Source Guard

Catalyst 3750-x