Chapter 41 Loop Guard
XS3800-28 User’s Guide
286
The following figure shows port
N
on switch
A
connected to switch
B
. Switch
B
has two ports,
x
and
y
,
mistakenly connected to each other. It forms a loop. When broadcast or multicast packets leave port
N
and reach switch
B
, they are sent back to port
N
on
A
as they are rebroadcast from
B
.
Figure 199
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 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
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 Switch then shuts down port
N
to ensure that the rest of the network
is not affected by the switch in loop state.
Figure 200
Loop Guard – Probe Packet
The Switch 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 Switch will shut down port
N
if it detects that the probe
packet has returned to the Switch.
Figure 201
Loop Guard – Network Loop
Note: After resolving the loop problem on your network you can re-activate the disabled port
through the Web Configurator or through commands (See the CLI Reference Guide).
Summary of Contents for XS3800-28
Page 29: ...29 PART I User s Guide...
Page 54: ...54 PART II Technical Reference...
Page 88: ...Chapter 4 Web Configurator XS3800 28 User s Guide 88 Figure 51 Online Web Help...
Page 148: ...Chapter 20 Cloud Management XS3800 28 User s Guide 148 Figure 94 SYSTEM Cloud Management...
Page 263: ...Chapter 36 OAM XS3800 28 User s Guide 263 Figure 182 PORT OAM OAM Status OAM Details...
Page 540: ...Chapter 72 VRRP XS3800 28 User s Guide 540 Figure 434 VRRP Example 2 VRRP Status on Switch B...
Page 581: ...Chapter 77 Policy Rule XS3800 28 User s Guide 581 Figure 456 Policy Example...