Brocade FastIron Ethernet Switch Security Configuration Guide - Manual (Page 345)

The following figure illustrates the SID packet format.
FIGURE 30 SID packet format
The second byte (N in the figure) is the length of the ASCII string that follows. The FastIron switch
supports up to 50 ASCII characters.
DHCP option 82 configuration
When DHCP snooping is enabled on a VLAN, DHCP option 82 also is enabled by default. You do not
need to perform any extra configuration steps to enable this feature. To enable DHCP snooping, refer
to
Enabling DHCP snooping on a VLAN on page 339.
When processing DHCP packets, the FastIron switch applies the following default behavior when DHCP
option 82 is enabled:
• Subjects all ports in the VLAN to DHCP option 82 processing
• Uses the general CID packet format
• Uses the standard RID packet format
• Replaces relay agent information received in DHCP packets with its own information
• Does not enable SID processing
When DHCP option 82 is enabled, you can optionally:
• Disable DHCP Option 82 processing on individual ports in the VLAN
• Configure the device to drop or keep the relay agent information in a DHCP packet instead of
replacing it with its own information
• Enable SID processing
Disabling and re-enabling DHCP option 82 processing on an individual interface
By default, when DHCP option 82 is enabled on a VLAN, DHCP packets received on all member ports
of the VLAN are subject to DHCP option 82 processing. You can optionally disable and later re-enable
DHCP option 82 processing on one or more member ports of the VLAN. To do so, use the commands
in this section.
To disable a particular port in a VLAN from adding relay agent information to DHCP packets, enter
commands such as the following.
device(config)#ip dhcp snooping vlan 1
device(config)#interface ethernet 1/4
device(config-if-e1000-1/4)#no dhcp snooping relay information
The first CLI command enables DHCP snooping and DHCP option 82 on VLAN 1. The second
command changes the CLI configuration level to the Interface configuration level for port e 1/4. The last
command disables DHCP option 82 on interface e 1/4, which is a member of VLAN 1.
DHCP option 82 configuration
FastIron Ethernet Switch Security Configuration Guide 345
53-1003088-03