Planet IGSW-2840 User Manual page 482

client's hardware address stored in the DHCP packet is the same as the source MAC address in the Ethernet header.
* If the DHCP packet is not a recognizable type, it is dropped. -If a DHCP packet from a client passes the filtering criteria
above, it will only be forwarded to trusted ports in the same VLAN.
- If a DHCP packet is from server is received on a trusted port, it will be forwarded to both trusted and untrusted ports
in the same VLAN.
If the DHCP snooping is globally disabled, all dynamic bindings are removed from the binding table.
Additional considerations when the switch itself is a DHCP client – The port(s) through which the switch submits a client
request to the DHCP server must be configured as trusted (ip dhcp snooping trust, page 4-149). Note that the switch will
not add a dynamic entry for itself to the binding table when it receives an ACK message from a DHCP server. Also, when
the switch sends out DHCP client packets for itself, no filtering takes place. However, when the switch receives any
messages from a DHCP server, any packets received from untrusted ports are dropped.
Example
Example
This enables DHCP snooping globally for the switch.
Console(config)#ip dhcp snooping
Console(config)#
Related Commands
ip dhcp snooping vlan
ip dhcp snooping trust
ip dhcp snooping vlan
This command enables DHCP snooping on the specified VLAN. Use the no form to restore the default setting.
Syntax
[no] ip dhcp snooping vlan vlan-id
vlan-id -ID of a configured VLAN (Range: 1-4094)
Default Setting
Disabled
Command Mode
Global Configuration
Command Usage
When DHCP snooping enabled globally using the ip dhcp snooping command (page 4-146), and enabled on a VLAN with
this command, DHCP packet filtering will be performed on any untrusted ports within the VLAN as specified by the ip dhcp
snooping trust command (page 4-149).
When the DHCP snooping is globally disabled, DHCP snooping can still be configured for specific VLANs, but the
changes will not take effect until DHCP snooping is globally re-enabled.
482
User's Manual of IGSW-2840