Potential impact of large broadcast domains
- by john
I recently switched jobs. By the time I left my last job our network was three years old and had been planned very well (in my opinion). Our address range was split down into a bunch of VLANs with the largest subnet a /22 range. It was textbook.
The company I now work for has built up their network over about 20 years. It's quite large, reaches multiple sites, and has an eclectic mix of devices. This organisation only uses VLANs for very specific things. I only know of one usage of VLANs so far and that is the SAN which also crosses a site boundary.
I'm not a network engineer, I'm a support technician. But occasionally I have to do some network traces for debugging problems and I'm astounded by the quantity of broadcast traffic I see. The largest network is a straight Class B network, so it uses a /16 mask. Of course if that were filled with devices the network would likely grind to a halt. I think there are probably 2000+ physical and virtual devices currently using that subnet, but it (mostly) seems to work. This practise seems to go against everything I've been taught.
My question is:
In your opinion and From my perspective - What measurement of which metric would tell me that there is too much broadcast traffic bouncing about the network? And what are the tell-tale signs that you are perhaps treading on thin ice?
The way I see it, there are more and more devices being added and that can only mean more broadcast traffic, so there must be a threshold. Would things just get slower and slower, or would the effects be more subtle than that?
