User's Manual

EnRoute50x/51x User’s Guide

TR0153 Rev. D2

10.2 Using a Centralized DHCP Server

DHCP relay enables assignment of IP addresses to wireless clients from a common remote

DHCP server. The remote DHCP server may reside either on a host connected to the mesh

gateway‟s wired segment, or on a server that is beyond one or more routers. When using a

common DHCP server, wireless clients are assigned IP addresses from a single address pool,

and are allowed to keep their IP address while roaming seamlessly from AP to AP. Even

though they will not move seamlessly from one node to another, wired clients can also have

their IP addresses assigned by a centralized server.

There are three classes of entities that must be configured when using this DHCP mode:

1. The individual EnRoute500s, including the repeaters and the gateway node

2. The central DHCP server

3. Any intermediate router(s) in the path between the DHCP server and the mesh cluster

gateway node

When using a centralized DHCP server, an address space, from which client IP addresses are

assigned, must be defined. The client interfaces on the EnRoute500s (there can be up to 5 per

node) must also have IP addresses that belong to this address space in order to facilitate

DHCP relay and selection of client IP addresses from the correct DHCP scope on servers that

serve hosts connected to different subnets. The client interface IP addresses need to be

configured statically. It is recommended that a contiguous range of IP addresses at either the

beginning or the end of the address space be set aside, one for each client interface on the

mesh nodes.

Consider the example where a mesh cluster consists of 3 nodes, including the gateway node.

The DHCP server resides on a host that also acts as the upstream router and is connected to

the mesh gateway‟s wired segment. We will set aside 15 IP addresses for the mesh nodes‟

client interfaces (3 nodes, up to 5 interfaces per node). Assuming the client address space is

192.168.5.0/24, with available addresses from 192.168.5.1 to 192.168.5.255, we will use

192.168.5.1 for the server hosting the DHCP server, 192.168.5.2 for the mesh gateway‟s

backhaul interface, set aside 192.168.5.3 to 192.168.5.18 for the mesh AP interfaces, and

configure the remote DHCP server to serve IP addresses in the range of 192.168.5.19 to

192.168.5.254 to wireless clients. We will keep 192.168.5.255 as the broadcast address for the

mesh cluster.

10.2.1 Configuring the EnRoute500s

When operating in centralized DHCP mode, Each EnRoute500 in a mesh cluster must be

configured to use centralized DHCP mode and to use the same centralized DHCP server. The

IP address of the central DHCP server is set with the DHCP relay server parameter. The

server must be reachable through the mesh cluster gateway‟s wired backhaul interface.