Configuration Guide User guide

1936 FastIron Configuration Guide
53-1002494-02
DHCP relay agent information
DHCP snooping configuration example
The following example configures VLAN 2 and VLAN 20, and changes the CLI to the global
configuration level to enable DHCP snooping on the two VLANs. The commands are as follows.
Brocade(config)#vlan 2
Brocade(config-vlan-2)#untagged ethe 1/3 to 1/4
Brocade(config-vlan-2)#router-interface ve 2
Brocade(config-vlan-2)#exit
Brocade(config)#ip dhcp snooping vlan 2
Brocade(config)#vlan 20
Brocade(config-vlan-20)#untagged ethe 1/1 to 1/2
Brocade(config-vlan-20)#router-interface ve 20
Brocade(config-vlan-20)#exit
Brocade(config)#ip dhcp snooping vlan 20
On VLAN 2, client ports 1/3 and 1/4 are untrusted by default all client ports are untrusted. Hence,
only DHCP client request packets received on ports 1/3 and 1/4 are forwarded.
On VLAN 20, ports 1/1 and 1/2 are connected to a DHCP server. DHCP server ports are set to
trusted .
Brocade(config)#interface ethernet 1/1
Brocade(config-if-e10000-1/1)#dhcp snooping trust
Brocade(config-if-e10000-1/1)#exit
Brocade(config)#interface ethernet 1/2
Brocade(config-if-e10000-1/2)#dhcp snooping trust
Brocade(config-if-e10000-1/2)#exit
Hence, DHCP server reply packets received on ports 1/1 and 1/2 are forwarded, and client IP/MAC
binding information is collected.
The example also sets the DHCP server address for the local relay agent.
Brocade(config)#interface ve 2
Brocade(config-vif-2)#ip address 20.20.20.1/24
Brocade(config-vif-2)#ip helper-address 1 30.30.30.4
Brocade(config-vif-2)#interface ve 20
Brocade(config-vif-20)#ip address 30.30.30.1/24
DHCP relay agent information
DHCP relay agent information, also known as DHCP option 82, enables a DHCP relay agent to
insert information about a clients’ identity into a DHCP client request being sent to a DHCP server.
When DHCP snooping is enabled on the FastIron switch, DHCP option 82 is automatically enabled.
DHCP packets are processed as follows:
• Before relaying a DHCP discovery packet or DHCP request packet from a client to a DHCP
server, the FastIron switch will add agent information to the packet.
• Before relaying a DHCP reply packet from a DHCP server to a client, the FastIron switch will
remove relay agent information from the packet.