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Setting up dhcp-helper

Setting up dhcp-helper

DHCP helper or dhcp relay is used in situations where a centralized or remote DHCP server is being used for address assignment.   In this case the client does not yet have an IP address so the request cannot be routed and requires the use of an agent to handle the routing.

Basic Setup

services dhcp-helper status enable server 10.4.75.145 listen LAN150

This listens for DHCP Requests (broadcast) entering LAN150 interface and then forwards them unicast to the DHCP server at 10.4.75.145

NOTE: LAN DHCP Server and dhcp-helper cannot both be enabled at the same time.

Multiple LAN’s

When setting up multiple LAN’s, since only one dhcp-helper can be enabled,  just enter multiple listeners.

services dhcp-helper status enable server 10.4.75.145 listen LAN150 listen VOICE

Bridge Setup

services dhcp-helper status enable server 10.4.75.145 listen LAN150

This is exactly the same as above with the exception that LAN150 uses a bridge port. Do not setup a static route to escape traffic from the bridge, this will not work (This is the initial Discover packet src 0.0.0.0.67 dst 255.255.255.0.68).

Relay over WAN Virtualization

services dhcp-helper status enable server 10.4.75.145 listen LAN150

extra_snat add entry enable source 10.200.0.0/16 destination 10.4.75.145/32 snat-ip 10.32.2.205 force-loose enable

dhcp-helper will be setup just like in a basic or bridge setup with the caveat that when the route to the DHCP server is over WAN Virtualization the source of the unicast request will be that of the WV tunnel ip. For this reason you will need to SNAT the source IP (usually to the LAN IP of the Ecessa) . Importantly use ‘force-loose’ so that it isn’t restricted to a WAN.

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