Broadcast Domains

[nicholas.gallagher]

On average, how many PC's or devices should there be in a broadcast domain to main a healthy LAN network.

[Jon Marshall]

Hi Nicholas

That is a bit of an open ended question really and you may get many different answers. A lot depends on how may of your applications that you run on your network rely on braodcast traffic.

Generally speaking, and it is generally, a Class C ie /24 would be the biggest. We use /25's here where i work which allows 126 hosts per subnet.

HTH

Jon

[glen.grant]

I agree with John a /24 is a comfortable size subnet which we have used for years and it makes for a very stable network environment and good response for all users .

[Kevin Dorrell]

I'll go along with that too, although it really depends how active the hosts are, and how paranoid is the NetAdmin.

Me, I'm known as the broadcast police 'cos I watch the background traffic like a hawk, and stomp on any machine that is not behaving. That way I can get away with well over the 250 or so devices a Class-C can offer. But I wouldn't recommend that to anyone else unless they are prepared to keep a close watch on the network.

I find a background noise of about 40 packets per second just about the limits of acceptability. It's an interesting exercise. Configure a switchport as access on the VLAN you are interested in, connect a network monitor to an unused NIC and collect packets for an hour or so. Most should be ARPs, some might be non-IP multicasts like CGMP (Ugh!), and maybe 1% will be flooded unicasts. Some will be stuff you really were not expecting unless you do this exercise regularly.

Kevin Dorrell

Luxembourg