Thursday, March 1, 2018

BPDU Flooding on Dell PowerConnect - what's it for?

Hello fellow netadmins of reddit.

I'm looking for some detail on the function, use and best practices of Dell's 'BPDU Flooding' feature on Powerconnect N-series and 2800 series switches. I've been having some trouble wrapping my head around this feature. Is there a Cisco analogue to this feature with a totally different name, as often seems to be the case with Dell stuff?

Some background:

I've been at the trade for about 20 years. Recently I have started working at a company with a larger amd wider switch infrastructure where our spanning tree and related configs matter. I'm tasked to ramp up on STP and related concepts, figure out what changes we need and implement.

We are mostly centered on the Dell PowerConnect N2/3/4000 series and a handful of older PowerConnect 2800's

I'm not having trouble with most concepts: root priorities, guard, STP states, portfast & related concepts like loop protection/keepalive -- for the most part I am figuring these out.

However all our Dell switches seem to support and talk about a feature called 'BPDU flooding' that I am having difficulty understanding. While I have found a lot of descriptions about what BPDU flooding does, I can't seem to find any examples of why one would want to do it.

I understand the related concepts of BPDU protection and BPDU filtering, but not how they relate to flooding. My older 2800's seem to force me to pick 'flooding or filtering' at a global level and don't mention 'protection' in their configs at all. The N-series have much more granular options. I haven't started modelling things in my lab, but am pretty much ready to proceed to that step except for not understanding this one point.

The book(s) has this to say about BPDU flooding, and not much else: "The BPDU flooding feature determines the behavior of the switch when it receives a BPDU on a port that is disabled for spanning tree. If BPDU flooding is configured, the switch will flood the received BPDU to all the ports on the switch which are similarly disabled for spanning tree."

I want to make sure I fully understand all of these concepts before I draft my final deployment plans, and this one is really escaping me. Google has let me down in my quest for knowledge today.

I guess my ultimate question is: can anyone tell me what BPDU flooding is specifically for? What problem does it solve, or scenario does it address? How does it fit into the other BPDU modes and the rest of the STP/switch management eco system? Any best practices tips?

Help me Reddit-wan-Kenobi, you are my only hope.



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