How big a vlan can be...?

[Prasan Venky]

Dear All,

If the users are more consider it requires /18 subnet to cover all users in a same vlan. So it will be a very big vlan. Is this normal or vlan should be small?

KVS

[paolo bevilacqua · Accepted solution]

There is no rule. As long you can manage it and it doesn't break, it is fine.

[Bilal Nawaz]

Exactly what Paolo said... As big as you want it to be.

(not advised to be big/massive though)

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[Jan Hrnko]

Hi,

I agree with gentlemen above, but there is one more thing on my mind.

As it is absolutely possible to create such a big vlan, please, do consider following.

If there will be such great ammount of hosts in one LAN/VLAN, there could be problems with broadcast traffic that could eventually lead to link congestion(maybe even switch cpu overloading) and therefore disruption of the network. It really depends on the parameters of the network and devices used.

Just an idea, maybe it's really not worth considering, but I would definitely think about it.

Best regards,

Jan

[Joseph W. Doherty · Accepted solution]

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Posting

As Jan notes, the issue with large subnets, such as your proposed /18, you often run into scability issues due to broadcasts.  Broadcast packets go to all hosts and all hosts need to open the packet to see what it's about.  Besides broadcasts, multicast can be a scability issue too, but newer network devices can often suppress sending undesired multicast to a host, and even when it cannot, the host's NIC often can decline to open it if it's not a multicast packet the host desires.

As a general rule, a /24 is considered a "safe" maximum, but much depends on how many hosts will actually be active at any one time and the nature of their data communications.

[InayathUlla Sharieff · Accepted solution]

Vlan is a broadcast domain, You can have all in one vlan but its quite difficult for you to manage.

The reason behind creating VLans is to manage the broadcast and your network easily.

HTH

Regards

Inayath