◦
To ensure that the lease time in the database is accurate, we recommend that you enable and
configure Network Time Protocol (NTP).
◦
If NTP is configured, the switch writes binding changes to the binding file only when the switch
system clock is synchronized with NTP.
•
If you want the switch to respond to DHCP requests, it must be configured as a DHCP server.
•
If you want the switch to relay DHCP packets, the IP address of the DHCP server must be configured
on the switch virtual interface (SVI) of the DHCP client.
•
To use the DHCP snooping option of accepting packets on untrusted inputs, the switch must be an
aggregation switch that receives packets with option-82 information from an edge switch.
•
You must configure the switch to use the Cisco IOS DHCP server binding database to use it for DHCP
snooping.
•
You must configure a destination on the DHCP snooping binding database to use the switch for DHCP
snooping.
•
For DHCP snooping to function properly, all DHCP servers must be connected to the switch through
trusted interfaces. In a service-provider network, a trusted interface is connected to a port on a device
in the same network.
•
You must globally enable DHCP snooping on the switch.
•
Before globally enabling DHCP snooping on the switch, make sure that the devices acting as the DHCP
server and the DHCP relay agent are configured and enabled.
•
Do not enable Dynamic Host Configuration Protocol (DHCP) snooping on RSPAN
VLANs. If DHCP snooping is enabled on RSPAN VLANs, DHCP packets might not
reach the RSPAN destination port.
Note
Related Topics
DHCP Snooping, on page 166
Enabling DHCP Snooping and Option 82
Beginning in privileged EXEC mode, follow these steps to enable DHCP snooping on the switch:
Catalyst 2960-XR Switch Security Configuration Guide, Cisco IOS Release 15.0(2)EX1
OL-29434-01 177
Configuring DHCP
Enabling DHCP Snooping and Option 82
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