[afnog] Bridged Access Network

[Mark Tinka]

On Wednesday, October 09, 2013 10:31:39 AM Vincent Mwamba 
wrote:

> We recently experienced a bad broadcast storm on our
> bridged(flat) access network caused by our customers
> sending broadcasts into our network.

Flat topologies don't scale very well, particularly at Layer 
2.

A little bit of hierarcy is necessary for various reasons, 
not least of which is scaling and containment of control or 
data traffic.

> Our current design
> is we have multiple high sites in a town which have
> WiMAX access points(bridged mode)/point to point
> radios/fttx terminating onto a switch, we see broadcasts
> from all these customers. We have seperated some of the
> services to have their own Vlans but as soon as the
> numbers grow in each Vlan we see these issues again. The
> customer traffic from each high site is carried over our
> layer 2 access back to a single aggregation router.
> Some High sites are aggregation points for more remote
> sites and for redundancy links, which has caused us
> spanning tree issues in the past.
> 
> What is the best way to grow the flat network and avoid
> spanning tree headaches.
> What is the best practice to provision the various
> services we offering to our customers and avoid
> broadcasts?
> How are other ISP doing it?

A couple of options, which will be a case of pain vs. money 
you can spend:

	1. Implement storm control mechanisms as supported 	
	   by your infrastructure.

	2. Configure each customer to be in their own VLAN. 
	   Forwarding between customers gets inefficient, 	
           as it has to go the nearest IP router and
           probably go back the same path, but it
	   eliminates cross-talk between customers and
	   helps fight broadcast storms (especially since
  	   the majority of traffic from customers is likely
	   headed to the Internet, not to other customers on
	   the same network.

	3. Distribute your access routing as much as your
	   budget can allow so that you're backhauling on IP
	   rather than Ethernet, thereby avoiding Spanning
	   Tree where able.

Cheers,

Mark.
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