Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 794)

764 Multi-Service IronWare Switching Configuration Guide
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DHCP snooping
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System reboot and the binding database
To allow DAI and DHCP snooping to work smoothly across a system reboot, the binding database is
saved to a file in the system flash memory after the user issues the “reload” command. DHCP
learned entries are written to the system flash memory before the device reboots. The flash file is
written and read only if DHCP snooping is enabled.
Configuring DHCP snooping
Follow the steps listed below to configuring DHCP snooping.
1. Enable DHCP snooping on a VLAN.
2. For ports that are connected to a DHCP server, change their trust setting to trusted.
The following table shows the default settings of DHCP snooping:
Enabling DHCP snooping on a VLAN
DHCP packets for a VLAN with DHCP snooping enabled are inspected.
DHCP snooping is disabled by default. This feature must be enabled on the client and the DHCP
server VLANs. To enable DHCP snooping, enter the following global command for these VLANs.
Brocade(config)#ip dhcp-snooping vlan 2
The command enables DHCP snooping for a VLAN or a range of VLANS.
Syntax: [no] ip dhcp-snooping vlan vlan-number [ to vlan_number] [ insert-relay-information]
The vlan-number variable specifies the ID of a configured client or DHCP server VLAN.
If the [insert-relay-information] option is enabled, then DHCP option 82 is inserted in all the DHCP
request packets. Refer to
“DHCP binding database” on page 763 for more information.
DHCP snooping suboptions
When the DHCP relay agent information option is enabled, the DHCP relay adds the option 82
information to packets it receives from clients, then forwards the packets to the DHCP server. The
DHCP server uses the option 82 information to decide which IP address to assign to the client or
the DHCP server may use the information in the option 82 field for determining which services to
grant to the client. The DHCP server sends its reply back to the DHCP relay, which removes the
option 82 information field from the message, and then forwards the packet to the client.
Option 82 information is made up of a series of suboptions. Brocade supports suboption 1,
suboption 2, and suboption 9.
• Agent Circuit ID (suboption 1) —An ASCII string identifying the interface on which a client DHCP
packet is received.
• Agent Remote ID (suboption 2) —An ASCII string assigned by the relay agent that securely
identifies the client.
Feature Default
DHCP snooping Disabled
Trust setting for ports Untrusted