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Community Member

Which is safer, RSTP&UDLD&PAGP or STP&UDLD&PAGP

Hello,

I am now considering of which technology combination is safer, RSTP&UDLD&PAGP or STP&UDLD&PAGP in the following simple design.

L2|======|L2

(Links between L2s is etherchannel.)

Could Loop happen if all the following situations happen before UDLD detect unidirectional link?

[situations]

1.PAGP is down

2.Unidirectional Link(One of Etherchannel) happens

3 REPLIES

Re: Which is safer, RSTP&UDLD&PAGP or STP&UDLD&PAGP

Hi,

If only these two switches are involved in the setup, the loop should not happen in the scenarios mentioned.

If Unidirectional link failure occurs in a bigger network( with multiple switches and redundant links between them), then it could potentially lead to loop/inconsistent topology detection in STP.

-VJ

Cisco Employee

Re: Which is safer, RSTP&UDLD&PAGP or STP&UDLD&PAGP

Hello,

If you have STP/RSTP enabled on the port, STP will eventually block one of the ports when PAgP is down.So the loop will not happen in this case.UDLD will take care of the loop detection when you have unidirectional situation.

-amit singh

Community Member

Re: Which is safer, RSTP&UDLD&PAGP or STP&UDLD&PAGP

Thanks a lot, amit singh, VJ for replying my post!My concern is that whether loop happens or not by the time UDLD detects unidirectional situation if RSTP is used instead of STP.

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