ZyXEL Communications GS2210-8 User Manual page 258

• I t will receive broadcast m essages sent out from t h e swit ch in loop st at e.
• I t will receive it s own broadcast m essages t hat it sends out as t hey loop back. I t will t hen re-
broadcast t hose m essages again.
The following figure shows port N on swit ch A connect ed t o swit ch B. Swit ch B is in loop st at e.
When broadcast or m ult icast packet s leave port N and reach swit ch B, t hey are sent back t o port N
on A as t hey are rebroadcast from B.
Figure 179 Swit ch in Loop St at e
A
The loop guard feat ure checks t o see if a loop guard enabled port is connect ed t o a swit ch in loop
st at e. This is accom plished by periodically sending a probe packet and seeing if t he packet ret urns
on t he sam e port . I f t his is t he case, t he Swit ch will shut down t he port connect ed t o t he swit ch in
loop st at e.
The following figure shows a loop guard enabled port N on swit ch A sending a probe packet P t o
swit ch B. Since swit ch B is in loop st at e, t he probe packet P ret urns t o port N on A. The Swit ch
t hen shut s down port N t o ensure t hat t he rest of t he net work is not affect ed by t he swit ch in loop
st at e.
Figure 180 Loop Guard - Probe Packet
A
The Swit ch also shut s down port N if t he probe packet ret urns t o swit ch A on any ot her port . I n
ot her words loop guard also prot ect s against st andard net work loops. The following figure
illust rat es t hree swit ches form ing a loop. A sam ple pat h of t he loop guard probe packet is also
shown. I n t his exam ple, t he probe packet is sent from port N and ret urns on anot her port . As long
as loop guard is enabled on port N . The Swit ch will shut down port N if it det ect s t hat t he probe
packet has ret urned t o t he Swit ch.
Chapter 27 Loop Guard
N
P
P
N
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B
B