[Babel-users] babeld usage for wifi mesh for festival in Germany

[Christof Schulze]

Hello everyone,

Babeld 1.8.4 was just used to create a mesh network for the german 
festival "Breminale". To accomplish client roaming, l3roamd was used.  
Multicast-Routing was enabled mesh-wide using mmfd. Before the network 
was taken down and replaced with a switched network it had 5-6K 
Routes and 1K client devices (with 58 Nodes with 2-4 used interfaces 
into every daemon on it).

This is proof that this type of setup is able to scale into the 
dimensions needed by Freifunk Communities in Germany. This is the 
largest real-life babeld installation that I know of and the fact that 
it was possible to pull it off is a great success. I could stop this 
email here, however the engineer in myself cannot deny that:
* Route distribution was slow at that network size to the point where 
  the network was unusable during peak times.
* Babeld was spending a lot of CPU time. (1.9 should help)
* mmfd was listening on the babeld status socket, burning 30% CPU.  
  Monitoring just neighbour changes would have significantly helped. To 
  address this, an architecture change is being implemented in mmfd such 
  that the dependency towards the babel socket is removed. This will 
  reduce the load as well.

I am extremely curious how the stack will perform next time this is 
attempted using babeld 1.9.

I thank the Freifunk Bremen team around genofire for allowing this type 
of experiment at that scale and for making it all happen, providing 
extremely valuably input for debugging and further developing the 
required software stack [1]. Thank you very much.

[1] https://github.com/FreifunkBremen/gluon-site-ffhb/tree/breminale2019-babel

Cheers
Christof


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