Zyxel OLT2412 Инструкция по эксплуатации онлайн [210/326] 154545

Chapter 27 Loop Guard

OLT2412 User’s Guide

210

Figure 53 Switch in Loop State

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 OLT will shut down the port connected to the switch in loop

state.

The following figure shows a loop guard enabled port N on switch A sending a probe packet P to

switch B. Since switch B is in loop state, the probe packet P returns to port N on A. The OLT then

shuts down port N to ensure that the rest of the network is not affected by the switch in loop state.

Figure 54 Loop Guard - Probe Packet

The OLT also shuts down port N if the probe packet returns to switch A on any other port. In other

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 N and returns on another port. As long as loop guard is

enabled on port N. The OLT will shut down port N if it detects that the probe packet has returned to

the OLT.

Figure 55 Loop Guard - Network Loop