Echelon LonWorks Router - Manual (Page 21)

the destination address is then checked to determine whether the message
should be forwarded or dropped. The forwarding flags are all cleared whenever
the router is reset, so the learning process restarts after a reset.
The forwarding flag for a given subnet should never be cleared on both sides of a
router. However, the flag can be cleared on both sides if a device is moved from
one side of a router to the other side. For example, if subnet 1 is located on side
A of a router, the router will learn subnet 1’s location as soon as it receives a
message generated by any device in subnet 1. If any subnet 1 device is moved to
side B without reinstalling it, the router will learn that subnet 1 is also on side B,
and will stop forwarding subnet 1 messages to side A. The router detects this
error and logs it, as described in Chapter 7, Network Management Messages.
Router receives
message packet
Is message addressed
to either of the router’s
domains?
Is message domain
length zero, source
subnet zero, addressed
as broadcast?
Drop packet
Is message source
subnet zero?
Is message domain
length zero, addressed
as broadcast?
Clear subnet fwd flag
Set message source subnet
= router subnet
Substitute one or both
domains from the router,
source subnet = our
subnet, dest subnet zero
Forward one or two
packets
No
Yes Yes Yes
No
Yes
No No
Page 2
* Applies to
learning
router only
Figure 4. Configured and Learning Router Forwarding Rules, Part 1
L ON W ORKS Router User’s Guide 11