Westermo RedFox Series - Manual (Page 520)

Westermo OS Management Guide
Version 4.17.0-0
problems at downstream relay agents when using the Forward, Append, Replace,
and Require policies. WeOS handling of packets on the return path from the DHCP
server may be modified in upcoming WeOS releases.
23.1.3 DHCP Proxy Mode
According to the RFC2131[ 7 ] a DHCP relay agent would only be involved in the
initial DHCP message, while subsequent DHCP lease renew messages would be
sent directly between client and server, as shown in
fig. 23.2 .
For many use-cases however, this behaviour is not desirable. In particular with
Option 82 (see
section 23.1.2 ) all DHCP messages from the client to the server
need to have this extra piece of information appended so that the server can
properly identify the client. This is called DHCP Proxy Mode, or DHCP Server
Identifier Override, defined in RFC5107[
18 ].
DHCP Discover
DHCP Offer
DHCP Request
DHCP Ack
DHCP Discover
DHCP Offer
DHCP Request
DHCP Ack
DHCP Ack
DHCP Renew Request
DHCP
Client
DHCP
Relay
DHCP
Server
time
Figure 23.2: Typically only the initial DHCP exchange is done via the relay agent,
while lease renew messages are sent directly (unicast) between client and server.
Most modern DHCP servers support RFC5107[ 18 ], which is a sub-option to Option
82. But some older DHCP servers do not and for this particular case the WeOS
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