ZyXEL Communications GS1350 Series User Manual page 197

The following figure shows port
mistakenly connected to each other. It forms a loop. When broadcast or multicast packets leave port
and reach switch , they are sent back to port
B
Switch in Loop State
Fig ure 142
The loop guard feature checks to see if a loop guard enabled port is connected to a Switch in loop
state. This is accomplished by periodically sending a probe packet and seeing if the packet returns on
the same port. If this is the case, the Switch will shut down the port connected to the switch in loop state.
Loop guard can be enabled on both Ethernet ports. The following figure shows a loop guard enabled
port on switch sending a probe packet
N A
packet returns to port
P N
is not affected by the switch in loop state.
Loop Guard – Probe Packet
Fig ure 143
The Switch also shuts down port
words loop guard also protects against standard network loops.
The following figure illustrates three switches forming a loop. A sample path of the loop guard probe
packet is also shown. In this example, the probe packet is sent from port
As long as loop guard is enabled on port
packet has returned to the Switch.
Loop Guard – Network Loop
Fig ure 144
Note: After resolving the loop problem on your network you can re-activate the disabled port
via the Web Configurator (see
Reference Guide).
on switch connected to switch
N A
on
N
to switch
P
on . The Switch then shuts down port
A
if the probe packet returns to switch
N
. The Switch will shut down port
N
Section 8.7 on page
GS1350 Series User's Guide
197
. Switch
B B
as they are rebroadcast from
A
. Since switch is in loop state, the probe
B B
to ensure that the rest of the network
N
on any other port. In other
A
and returns on another port.
N
if it detects that the probe
N
99) or via commands (See the CLI
has two ports, and ,
x y
N
.
B