Use this command to enable DHCP/BOOTP relay and the forwarding of local UDP broadcasts specifying a new destination address.
| address | Specifies a destination address used by forwarded local UDP broadcasts. |
| global | (Optional) Specifies that the default global forwarding table will be used for route lookup. |
| vrf vrf-name | (Optional) Specifies that the routing table of the specified VRF will be used for route lookup. |
| access-list acl-name | (Optional) Specifies the standard or extended IP access list to be applied to inbound UDP frames. |
None.
Configuration command, Interface configuration.
This command works in conjunction with the ip forward-protocol command, which defines the forward protocol and port number. You can use this command to add more than one helper address per interface.
When enabling DHCP/BOOTP relay and forwarding local UDP broadcasts to a new destination address that is located on a different VRF or the global router, the destination VRF router must be specified in the ip helper-address command. Use the vrf vrf-name parameter to specify a destination VRF or the global parameter to specify the global router as the destination.
When forwarding the local UDP broadcasts from a VRF to a destination address on a different VRF, the DHCP relay agent needs to include information about itself in order for the DHCP server to determine which pool of client addresses to pull the lease from. Including Option 82 in the DHCP relay information provides the required DHCP relay information.
Use the ip dhcp relay information option server-override or ip dhcp relay information option vpn commands described in this chapter to include DHCP relay agent information in the packet sent to the server by the DHCP relay agent.
The “no” form of this command disables the forwarding of UDP datagrams to the specified address
This example shows how to permit UDP broadcasts from hosts on networks 191.168.1.255 and 192.24.1.255 to reach servers on other networks:
System(rw)->configure System(rw-config)->ip forward-protocol udp System(rw-config)->interface vlan.0.5 System(rw-config-intf-vlan.0.5)->ip helper-address 192.168.1.255 System(rw-config-intf-vlan.0.5)->exit System(rw-config)->interface vlan.0.2 System(rw-config-intf-vlan.0.2)->ip helper-address 192.24.1.255
The following example:
System(su)->router Alpha-Group System(su-*ha-Group)->configure System(su-*ha-Group-config)->ip forward-protocol udp System(su-*ha-Group-config)->interface vlan.0.10 System(su-*ha-Group-config-intf-vlan.0.10)->ip helper-address 134.141.95.105 vrf Internet-Access System(su-*ha-Group-config-intf-vlan.0.10)->exit System(su-*ha-Group-config)->ip dhcp relay information option vpn System(su-*ha-Group-config)->
Print
this page
Email this topic
Feedback
View PDF
Download EPUB