Jon Marshall Thu, 11/22/2007 - 07:12
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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.



glen.grant Thu, 11/22/2007 - 07:16
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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 Thu, 11/22/2007 - 07:46
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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



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