Reference Guide

Dynamic Host Configuration Protocol (DHCP) | 257
Binding table entries are deleted when a lease expires, or the relay agent encounters a DHCPRELEASE,
DHCPNACK, DHCPDECLINE.
Enable DCHP snooping
Add a static entry in the binding table
Clear the binding table
Display the contents of the binding table
FTOS Behavior: Introduced in FTOS version 7.8.1.0, DHCP Snooping was available for Layer 3 only and
dependent on DHCP Relay Agent (
ip helper-address). FTOS version 8.2.1.0 extends DHCP Snooping to Layer 2,
and you do not have to enable relay agent to snoop on Layer 2 interfaces.
FTOS Behavior: Binding table entries are deleted when a lease expires or when the relay agent encounters a
DHCPRELEASE. Starting with FTOS Release 8.2.1.2, line cards maintain a list of snooped VLANs. When the
binding table is exhausted, DHCP packets are dropped on snooped VLANs, while these packets are forwarded
across non-snooped VLANs. Since DHCP packets are dropped, no new IP address assignments are made.
However, DHCPRELEASE and DHCPDECLINE packets are allowed so that the DHCP snooping table can
decrease in size. Once the table usage falls below the maximum limit of 4000 entries, new IP address assignments
are allowed.
Note: DHCP server packets will be dropped on all untrusted interfaces of a system configured for DHCP
snooping. To prevent these packets from being dropped, configure
ip dhcp snooping trust on the
server-connected port.
Step Task Command Syntax Command Mode
1 Enable DHCP Snooping globally.
ip dhcp snooping
CONFIGURATION
2 Specify ports connected to DHCP servers as trusted.
ip dhcp snooping trust
INTERFACE
3 Enable DHCP Snooping on a VLAN.
ip dhcp snooping vlan
CONFIGURATION
Task Command Syntax Command Mode
Add a static entry in the binding table.
ip dhcp snooping binding mac
EXEC Privilege
Task Command Syntax Command Mode
Delete all of the entries in the binding table
clear ip dhcp snooping binding
EXEC Privilege
Task Command Syntax Command Mode
Display the contents of the binding table.
show ip dhcp snooping
EXEC Privilege