[afnog] Bridged Access Network

[Chris Wilson]

Hi Vincent,

On Wed, 9 Oct 2013, Vincent Mwamba wrote:

> What is the best way to grow the flat network and avoid spanning tree headaches.

I think it's considered best practice is to avoid flat networks! 
(large broadcast domains)

Remember that two devices that can communicate directly with each other 
(are basically peers) can attack each other, and there's nothing you can 
do about it at the network level. You can defend the individual devices 
against the attacks, or prevent them from mounting attacks on others, to 
the extent that you control them and their OS supports it, and that's 
about it.

> What is the best practice to provision the various services we offering 
> to our customers and avoid broadcasts? How are other ISP doing it?

I don't know if it's a "best practice", but if your wimax devices support 
it, and you control them, then you could reconfigure them to block 
outbound broadcast traffic. Give them a static ARP entry for the gateway, 
and that's it. Without broadcast ARP, they won't be able to discover each 
other, and that's fine as they have no need to talk to each other.

Even if your network is physically flat, you may be able to logically 
partition it using a separate /30 subnet for each device, which only 
contains the device and the gateway. Then devices will not try to talk to 
each other.

Broadcasts should not actually bring the network down. No one node should 
be able to generate traffic that unfairly squeezes the traffic of other 
nodes off the network. The wimax head end should be allocating transmit 
slots fairly to all client device. If not, it needs to be fixed. Otherwise 
the same problem will keep repeating in different forms that have nothing 
to do with broadcast, just heavy traffic of all other kinds.

Cheers, Chris.
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