how many user per vlan is recommeded by cisco

[satukoivikko]

Hi,

Does anyone know what is Cisco's today recommendation about what is the maximum number of user per one vlan?.

We are planning to cut off some vlans, but because we have about 4000 clients in our network, I have a feeling, that 4000 clients are too much for one vlan.

[Anand Narayana]

hi,

you can create different vlans on your network, ofcourse 4000 clients on a single vlan is not at all advisable as it would be difficult to identify problems on the network(particularly when broadcast occurs). so you can segment your network by department wise, as an example let us say that in you organization you have server,mktg,advt,accounts,admin etc.... each department lets say max of 100 PC, so create seperate vlans like server lan, mktg vlan, advt vlan etc... for each department & do inter-vlan routing for communicating each other. by doing this, it will easy for you to understand the network, even while trouble shooting the network problems also becomes easy & there is no possibility that when a broadcast storms occurs in any other vlan, it will not affect to the other vlans on the network as the purpose of having vlans is mainly to segment the network for avoiding broadcasts & secondly for security by restricting some vlans to communicate each.

hope you understood.

rate this post if clear.

[Sureshdank]

Cisco recommends not more than 254 clients per VLAN

[satukoivikko]

254 clients is the number I rememberd too, but wasn't sure. Is that the newest recommendation from Cisco ? 254 sounds so small. I don't want to take care of over 15 vlans + all the vlans in server enviroment. We have about 10 client vlans now, which means that in 1 vlan we have 200-500 clients and everything has gone well without problems. We would like to cut off some of the vlans, because we are planning to move using dynamic vlan.

[mahmoodmkl]

Hi

In addtition to above posts u can think that a seprate subnet for each vlan.

Thanks

Mahmood

[Sureshdank]

You can go for Dynamic VLANs. But these days it is not comming into implementation much.

I would recommend you to go for Static VLANs, as you will have complete control over it on the switches itself. Dont fear about the number of VLANs. There are many companies which are having nearly 150 vlans.

HTH

Regards,

Suresh Jain

[ajayvmccie]

Can u give a link or valid document in CISCO refrencing only 254 users can be there in a VLAN

[glen.grant]

Like everyone else said , a /24 mask would work in most cases . 4000 clients in one vlan , ouchhhhhhhhhh . That is one big broadcast domain surprised they aren't bitching about performance . a /24 as everyone has said gives 254 working hosts per subnet , so you are looking at breaking up your network into about 16 separate subnets (vlans) . A big job to be sure but one that would give you a much improved network.

[yvk.kishore]

4000 is really a big number.. actually there is no such recomendation by cisco about how many hosts per vlan.... but says donot use more hosts in a vlan for broadcast problem.... so i think you should see the capabitily of switch like its speed,its features and then design accordingly...

hope this will help you....

[mheusinger]

Hello,

I have seen as much as 12000 hosts in a VLAN (good old Cat5500 days though). Brodcast was THE issue, but routers did not have the required forwarding performance in those days. The very moment the required layer3 performance was available the design was changed.

The main limitation to the number of hosts in a VLAN is the broadcast (or multicast) traffic and unknown unicast traffic generated by those hosts. Assume a (in reality nonexistant) host only using layer2 broadcast to arp for the default gateway. Then this would allow for a large number of hosts in a single VLAN.

Still I would not recommend it for other reasons. One reason is that a VLAN also is a failure domain. Assume one faulty NIC producing 100 Mbps of broadcasts all the time - all hosts in the VLAN would have performance issues. Or assume someone installs a multicast server and no IGMP snooping is configured in the switches. Again the traffic would be forwarded to all ports in the VLAN.

So it depends on your requirements how many hosts you want in a single VLAN. The recommendataion is to have one VLAN per access switch if possible. Usually this means 24 or 48 ports and hosts. Use Layer3 distribution switches and a routed core to get smaller broadcast and failure domains.

Hope this helps! Please rate all posts.

Regards, Martin

[rgodden]

top down design by oppenheimer has guidelines of 200 hosts per vlan for mixed protcols and 500 for pure ip .