Section 23.1.2 – Westermo RedFox Series User Manual
Page 517
Westermo OS Management Guide
Version 4.17.0-0
The DHCP server should also be configured with other relevant settings, e.g.,
default gateway, lease times, etc. (see
❼ Running relay agents on routers or switches: Relay agents can be run as
dedicated servers (RA3), but are typically located inside the local routers
(RA1 and RA2). By running the relay agents inside the routers, deploy-
ment and management costs are reduced, since no additional equipment
is needed.
Although not shown in
, it is also possible to run relay agents on
(layer-2) switches. This is useful when you wish to assign IP addresses based
on the physical port the PC connects to (see
for information
on DHCP Option 82). In such use cases, you may also wish to run several
relay agents within the same LAN –
provides more information
on running relay agents in switched networks.
As of WeOS v4.17.0, it is only possible to run a single relay agent instance per
WeOS unit. This is no major limitation, but implies, e.g., that a relay agent serv-
ing multiple LANs (RA2 in
) can not be configured to forward the DHCP
requests from different LANs to different sets of DHCP servers.
23.1.2
DHCP Option 82
The relay agent information option (DHCP option 82, see RFC3046[
]) enables
a relay agent to pass information to the DHCP server regarding which port the
DHCP request came in on. Thus, an option 82 aware DHCP server would be able
to assign IP settings (IP address, etc.) to a PC based on the port the PC connects
to.
The DHCP option 82 contains two sub-options, Circuit ID and Remote ID:
❼ Circuit ID: The circuit ID identifies the port on the relay agent, where the
DHCP request was received. Since the circuit ID can only be considered
unique within the reporting relay agent, the DHCP server generally needs
to consider both the circuit ID and an identifier of the specific relay agent
(e.g.,giaddr or option-82 remote ID, see below) when processing the DHCP
request.
In WeOS the circuit ID can be set according to the following methods:
– Disabled: When circuit ID is disabled, no circuit ID sub-option is passed
as part of the Relay Agent Information option (DHCP option 82).
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