[pox-dev] What does "Not flooding , holddown active " refer to ?

[Murphy McCauley]

On Oct 9, 2012, at 2:06 PM, Weiyang Mo wrote:
> I use your pox /murphypox .  Becasue thi version solves a lot more bugs which are necessary for me.

Just so you know, my fork is no longer moving: the changes are now merged into the betta branch of the main repository (which has a lot of development since then too).
 
> Here I run  "  sudo ./pox.py log.level --WARNING l2_multiUDP openflow.spanning_tree manageflow
>  
> The thing is that sometimes I can see that " Not flooding, holding down active" appear, when this appears, it seems that switches refuse to flood other than the one which connects to source.  From Sam's message, it seems that this is a self protection to avoid overload, but it shouldn't happen with spanning_tree and 100pkts/sec packets.

With l2_multi, switches won't flood for a "hold down" period -- the first five seconds after they connect.  This gives a chance to learn some destinations before starting flooding.  It's not entirely just to protect POX from overload, but to prevent from totally spamming the network, potentially flooding into loops, etc. when switches have just connected.  This also gives a silent moment for discovery to figure out connectivity and for a spanning tree to be built.

If you wait for five seconds after the switches connect before running your tests, you shouldn't see this message.  You can also adjust the FLOOD_HOLDDOWN variable in l2_multi (or your variant) to decrease the time before switches are willing to flood (you could set it to 0, for example).

-- Murphy