Spanning tree guard loop command behaviour

[mahesh18]

Hi Everyone,

I have question here command

spanning-tree guard loop.

First I enable it on single port which has fibre connection to switch 2.

This is what I found

On switch 1 port where I enable this I took 1 fibre cable out and port went from up to down state.

On switch 2 where there is no guard loop configured that port went into errdisable state.

Then on switch 2 also I config the command ----------- spanning-tree guard loop.

Then on switch 1 I took single fibre cable out.

Both switch ports are down down and no port is errdisabled?

So my question is is this default behaviour of guard loop command on both the caes?

[handoko wiyanto]

hi,

im reading a chapter about that feature here:

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080094640.shtml

regards,

[smehrnia]

Nah! this is not a default behaviour, looks weird if i got u right! what else you have configured on ur adjacent ports?

is UDLD by any chance enabled on swicthes? w.e.i.r.d.

Soroush.

[mahesh18]

Hi Soroush,

No udld is configured.

Thanks

[handoko wiyanto]

hm..

im just curious. when you only have two switches, and there are no loop link, what would you use stp anyway?

humor me

[smehrnia]

Handoko, I tell you why....

Loop guard is a feature to prevent unidirectional loops (esp fiber optic connections) same as UDLD, so it doesnt matter how many switches, also, it is always advised to use STP under all circumstances since u never know when n how a topology change might occure.

an a Last comment: he might be trying to test this commands and behaviours in a LAB environment did i answered u, haha...

Soroush.

[handoko wiyanto]

Soroush,

did what you ask

i even add you as a friend. so next time its a friends question LOL !!

[handoko wiyanto]

oh damn.

its right on the bottom part of the docs that i read !!

Loop Guard versus UDLD

hahaha..