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Community Member

Recommended number of hosts per broadcast domain?

Hi there

I know this is going to be a 'depends' answer, but I was looking for a guideline. I seem to recall a Cisco recommendation regarding the number of hosts in a broadcast domain. This was for an IP only network, IPX only network, IP and IPX mixed, Appletalk only etc. The numbers I remember are 400 for IP only, 200 for IP and IPX.

Can anyone point me in the right direction for some information?

Thanks

John

2 REPLIES
Bronze

Re: Recommended number of hosts per broadcast domain?

My own personal experience is to follow your TCP/IP subnet boundries, and remember the smaller the better.

Example - 10.0.0.0 255.255.255.0 gives host 1 - host 254. This means 254 devices will be completing for bandwidth. In a switched environment perhaps this is not a problem unless all 254 host are communicating at 100Mb/sec. all at the same time. 254 x 100 = 2540Mb/sec or 2,540,000,000 - This could easily overscribe the back plane of your switch, or any server in the broadcast domain. Larger subnets will only amplify the issue.

Hope this helps.

Frank

Community Member

Re: Recommended number of hosts per broadcast domain?

This is how I resonded to another posting.

I have heard many numbers, however I believe they are all system specific. You can have 100 and be getting killed if you have a desktop with a million protocols running, or 1000 if the desktop is configured locked down. In addition your desktop speed and NIC are determining factors. Basically the reasoning behind the numbers is that for every errant packet/frame on the line every workstation and/or NIC have to spend time looking at the information and say "is this for me?" If you have an intelligent NIC or a fast processor it will have less of an effect then if you are using older equipment. Put a sniffer on the LAN and take a peek as to what your traffic really is.

So I don't know if any information from any source will help you because most networks are different. Anyway those numers you said I have heard and was probably a guideline 2-3 years ago. What we do today that works well for our clients, is we subnet each floor into a VLAN (broadcast domain) down to a Class C.

Good Luck

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