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New Member

A network for 300 hosts in a single subnet.

Hi Folks,

I'm planning to create a network for 320 hosts, I'll use a class B address 172.16.0.0 with a subnet mask 255.255.254.0 so the valid host range will be

172.16.0.1 - 172.16.1.254. Is it a good idea? or any suggestion will be appreciated? Thanks.

2 ACCEPTED SOLUTIONS

Accepted Solutions
Purple

A network for 300 hosts in a single subnet.

  Personally I would never go more than a /23 network  and even then it would depend how heavy the traffic is on the subnet .   You are also affecting a lot more people if you have an issue  on the subnet if you have a single subnet as opposed to multiple subnets  at a /24 .

Super Bronze

A network for 300 hosts in a single subnet.

Disclaimer

The     Author of this posting offers the information contained within this     posting without consideration and with the reader's understanding  that    there's no implied or expressed suitability or fitness for any   purpose.   Information provided is for informational purposes only and   should not   be construed as rendering professional advice of any kind.   Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In     no event shall Author be liable for any damages whatsoever   (including,   without limitation, damages for loss of use, data or   profit) arising  out  of the use or inability to use the posting's   information even if  Author  has been advised of the possibility of  such  damage.

Posting

But what's the maximum number of host can I have in a single broadcast domain?? taking into account QoS, network congestion etc...??

That's the 64 bit question, and "it depends".

Broadcasts have two principle adverse effects.  The consume bandwidth.  They force hosts to examine them, even if they are not relevant to the receiving host.

Broadcasts can also easily trigger high network usage.  (For example, one broadcast ping might have every host issue a ping reply.)

Picking a subnet size, to handle a specific number of hosts, really has much to do with network usage expectations especially concerning broadcasts.  /24 is popular as typically we rarely encounter broadcast related issues on that size network with typical hosts with typical network usage.

Assuming overall broadcast frequency and bandwidth usage is consistent regardless of host's NIC bandwidth, higher NIC bandwidth's with better host processing performance should allow for higher number of hosts per subnet.  I.e. newer hosts with "faster" LAN would allow many more hosts per subnet.  However, the risk is, this assumes linear expansion, but with broadcast, especially with DoS attacks, broadcasts can trigger exponential network consumption (i.e. broadcast storm).

In your case, real world, if you have 100 Mbps or better switched network, but no L3 switch, I wouldn't be too concerned about 300 modern typical hosts on one L2 broadcast domain.  However, if you also had a L3 switch, I would probably keep to the traditional /24.

8 REPLIES
Hall of Fame Super Gold

A network for 300 hosts in a single subnet.

Is that enough???

<510 available IP addresses is enough?

New Member

A network for 300 hosts in a single subnet.

Yes Sir,

It will be enough for 320 hosts !! Ain't it?

Hall of Fame Super Gold

A network for 300 hosts in a single subnet.

Tell you what ...

Configure for /23 but reserve a /22.  If you ran out ...

New Member

A network for 300 hosts in a single subnet.

Thanks good idea too.

But what's the maximum number of host can I have in a single broadcast domain?? taking into account QoS, network congestion etc...??

Purple

A network for 300 hosts in a single subnet.

  Personally I would never go more than a /23 network  and even then it would depend how heavy the traffic is on the subnet .   You are also affecting a lot more people if you have an issue  on the subnet if you have a single subnet as opposed to multiple subnets  at a /24 .

New Member

A network for 300 hosts in a single subnet.

yeah a /23 is better than a /22 especially when dealing with VOIP traffic but we can't neither have multiple subnets at a /24 because we use several gateways for ADSL connections. Thanks glen.

Super Bronze

A network for 300 hosts in a single subnet.

Disclaimer

The     Author of this posting offers the information contained within this     posting without consideration and with the reader's understanding  that    there's no implied or expressed suitability or fitness for any   purpose.   Information provided is for informational purposes only and   should not   be construed as rendering professional advice of any kind.   Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In     no event shall Author be liable for any damages whatsoever   (including,   without limitation, damages for loss of use, data or   profit) arising  out  of the use or inability to use the posting's   information even if  Author  has been advised of the possibility of  such  damage.

Posting

But what's the maximum number of host can I have in a single broadcast domain?? taking into account QoS, network congestion etc...??

That's the 64 bit question, and "it depends".

Broadcasts have two principle adverse effects.  The consume bandwidth.  They force hosts to examine them, even if they are not relevant to the receiving host.

Broadcasts can also easily trigger high network usage.  (For example, one broadcast ping might have every host issue a ping reply.)

Picking a subnet size, to handle a specific number of hosts, really has much to do with network usage expectations especially concerning broadcasts.  /24 is popular as typically we rarely encounter broadcast related issues on that size network with typical hosts with typical network usage.

Assuming overall broadcast frequency and bandwidth usage is consistent regardless of host's NIC bandwidth, higher NIC bandwidth's with better host processing performance should allow for higher number of hosts per subnet.  I.e. newer hosts with "faster" LAN would allow many more hosts per subnet.  However, the risk is, this assumes linear expansion, but with broadcast, especially with DoS attacks, broadcasts can trigger exponential network consumption (i.e. broadcast storm).

In your case, real world, if you have 100 Mbps or better switched network, but no L3 switch, I wouldn't be too concerned about 300 modern typical hosts on one L2 broadcast domain.  However, if you also had a L3 switch, I would probably keep to the traditional /24.

New Member

A network for 300 hosts in a single subnet.

Thanks JosephDoherty,that's really helpful but unfortunately there's no L3 switch in our network and they don't want to invest in networking equipements, as network admin we all know the importance of a better switch and VLAN.




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