Binding table entries are deleted when a lease expires or when the relay agent encounters a DHCPRELEASE. 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. Because 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. After the table usage falls below the
maximum limit of 4000 entries, new IP address assignments are allowed.
NOTE: DHCP server packets are dropped on all not trusted interfaces of a system congured for DHCP snooping. To prevent
these packets from being dropped, congure ip dhcp snooping trust on the server-connected port.
Enabling DHCP Snooping
To enable DHCP snooping, use the following commands.
1 Enable DHCP snooping globally.
CONFIGURATION mode
ip dhcp snooping
2 Specify ports connected to DHCP servers as trusted.
INTERFACE mode
INTERFACE PORT EXTENDER mode
ip dhcp snooping trust
3 Enable DHCP snooping on a VLAN.
CONFIGURATION mode
ip dhcp snooping vlan name
Enabling IPv6 DHCP Snooping
To enable IPv6 DHCP snooping, use the following commands.
1 Enable IPv6 DHCP snooping globally.
CONFIGURATION mode
ipv6 dhcp snooping
2 Specify ports connected to IPv6 DHCP servers as trusted.
INTERFACE mode
ipv6 dhcp snooping trust
3 Enable IPv6 DHCP snooping on a VLAN or range of VLANs.
CONFIGURATION mode
ipv6 dhcp snooping vlan vlan-id
Adding a Static Entry in the Binding Table
To add a static entry in the binding table, use the following command.
• Add a static entry in the binding table.
EXEC Privilege mode
ip dhcp snooping binding mac
Dynamic Host
Conguration Protocol (DHCP) 307
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