IP address range

[Joe Lee]

Hello,

I want to create the VLAN on the switch and we need to have a big address pool of /22 bits. What is the advantage and disadvantage of /24 bit and /22 bits in a single VLAN? Please advise.

Regards,

Joe

[Richard Bradfield · Accepted solution]

Joe,

The main disadvantage of having a /22 network as opposed to a /24 Vlan, is the broadcast domain. There is always a certain amount of broadcast "noise" on a network. and Broadcast packets go to every port on that Vlan so having up to 4 times as many hosts on a /22 means you are going to get 4 times the Broadcast traffic. it is always better to break the network down into smaller Subnets.

I can't really see any advantages of a /22 over a /24 from a performance point of view, the only possible advantage would be from a management point of view less configuration required on switches and routers.

HTGH

Richard

[Richard Burts]

Joe begins his question by stating that they need a big address pool of /22 bits. And then he asks about advantages of smaller vs larger subnets. It seems to me that this asks about advantages after the decision is already made. So I will ask Joe why (or how) they have already decided that they need a very large address pool?

I agree with Richard that the primary issue is the size of the broadcast domain which does affect the amount of broadcast traffic. I would suggest that the other issue is about how many devices need to communicate directly with each other (ARP and communicate directly at layer 2) vs communicate using the gateway to access remote subnets.

HTH

Rick

[Joseph W. Doherty]

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Posting

As both other Ricks have already noted, the principle issue that limits the size of a flat network is broadcasts.  The issue with broadcasts, besides every device getting them all, every host must actually examine/process them to see if what the broadcast contains impacts the host.

On modern switched IP networks, with FE or better links and modern hosts, in my experience, usually a /22 works without issue.

One advantage of using a /22 over a /24, (discounting aggregation), your routing protocol only needs to deal with one route rather than four.

PS:

BTW, for some wireless, AP clients don't get broadcasts the same as do wired clients, so we've found larger user subnets, like a /22, works well for those.