MES53xx, MES33xx, MES23xx Ethernet Switch Series
160
In order to use Option 82, the device must have DHCP relay agent function enabled. To
enable DHCP relay agent function, use the 'ip dhcp relay enable' command in the global
configuration mode (see the appropriate section of the operation manual).
To ensure the correct operation of DHCP snooping feature, all DHCP servers used must be
connected to trusted switch ports. To add a port to the trusted port list, use the 'ip dhcp
snooping trust' command in the interface configuration mode. To ensure proper protection,
all other switch ports should be deemed as 'untrusted'.
Global configuration mode commands
Command line prompt in the global configuration mode is as follows:
console(config)#
Table 5.175. Global configuration mode commands
Command
Value/Default value
Action
ip dhcp snooping
-/disabled
Enable DHCP management for the switch.
no ip dhcp snooping
Disable DHCP management for the switch.
ip dhcp snooping vlan
vlan_id
vlan_id: (1..4094)/disabled
Enable DHCP management for a specific VLAN.
no ip dhcp snooping vlan
vlan_id
Disable DHCP management for a specific VLAN.
ip dhcp snooping
information option
alloweduntrusted
By default, ingress DHCP
packets with Option 82
from untrusted ports are
blocked.
Allow egress DHCP packets with Option 82 from untrusted
ports.
no ip dhcp snooping
information option
alloweduntrusted
Deny ingress DHCP packets with Option 82 from untrusted
ports.
ip dhcp snooping verify
Verification is enabled by
default.
Enable verification of client and source MAC addresses
received in a DHCP packet on untrusted ports.
no ip dhcp snooping verify
Disable verification of client and source MAC addresses
received in a DHCP packet on untrusted port.
ip dhcp snooping database
Backup file is not used
Enable the use of a DHCP management backup file (database).
no ip dhcp snooping
database
Disable the use of a DHCP management backup file (database).
ip dhcp information option
-/enabled
Allow the device to add Option 82 to DHCP messages.
no ip dhcp information
option
Prohibit adding Option 82 to DHCP messages.
Table 5.176. Option 82 field format as per TR-101 recommendations
Field
Information sent
Circuit ID
Device hostname.
string in the following format: eth <stacked/slotid/interfaceid>:<vlan>
The last byte is the number of the port that the device sending a DHCP request is connected
to.
Remote agent ID
Enterprise number – 0089c1
Device MAC address
Table 5.177. Option 82 field format in custom mode
Field
Information sent
Circuit ID
Length (1 byte)
Circuit ID type
Length (1 byte)
VLAN (2 bytes)