Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Does a vlan require a extra host for VLSM

Basically I'm using the IP 192.168.0.0/16 on a network I'm making.

I have:

Staff: 250 hosts

Support: 30 hosts

Admin: 8 hosts

Servers: 5 hosts

HR: 50 hosts

Do i need to basically add 1 on to each so staff is 251 hosts.

I know we need to use a default gateway for VLAN.

I'm going to be using a 4 vlans and servers will be left as it is.

3 REPLIES
Silver

Does a vlan require a extra host for VLSM

Hi,

See this below:

Network:   192.168.0.0/16    

Broadcast: 192.168.255.255      

HostMin:   192.168.0.1          

HostMax:   192.168.255.254      

Hosts/Net: 65534  

With this as you see you will have 65534 addresses available to assign. Normally you can use 192.168.0.1 for the gateway address and the rest can be assign for the hosts that you have on your network, excluding the network and broadcast addresses.

Hope this helps.

Hall of Fame Super Silver

Does a vlan require a extra host for VLSM

Leo

Your response would be quite appropriate if you read the first line of the original post and then composed your response without reading further. But if you read further and especially when you get to this line

I'm going to be using a 4 vlans and servers will be left as it is

then it becomes very evident that treating it as a single network space /16 is not the appropriate response.

Lee

I am not clear where you are going with this statement

Do i need to basically add 1 on to each so staff is 251 hosts. As I think about how you ask the question I wonder if this is an attempt to include/add an address for the gateway for each vlan.

But if you think carefully and clearly about the situation that you describe it becomes a series of questions about classical subnetting:

- if Staff needs 250 hosts then what subnet is large enough (but not larger) to fit 250 hosts? answer is /24. (with 254 usable host addresses)

- if Support needs 30 hosts then what subnet is large enough (but not larger) to fit 30 hosts? answer is /27. (with 30 usable host addresses) But if we also need to allow an address for the gateway (if there really are 30  Support hosts) the the address requirement becomes 31 and the subnet becomes a /26 (with 62 host addresses)

- if Admin needs 8 hosts then what subnet is large enough(but not larger) to fit 8 hosts? answer is /28. (with 14 usable host addresses) note that this may be a bit tricky since a /29 actually has 8 addresses but if you reserve an address for the subnet and an address for the broadcast then it is no longer large enough for 8 hosts.

- if Server needs 5 hosts then what subnet is large enough (but not larger) to fit 5 hosts? answer is /29. (with 6 usable host addresses)

- if HR needs 50 hosts then what subnet is large enough (but not larger) to fit 50 hosts? answer is /26. (with 62 usable hosts addresses)

HTH

Rick

Hall of Fame Super Blue

Re: Does a vlan require a extra host for VLSM

Lee

Rick has done a good job of showing how you break down the 192.168.0.0/16 to meet your needs.

In answer to your specific question in terrms of a gateway IP, yes each vlan/IP subnet will need some addresses reserved for the actual networking equipment. A common setup is to use something like HSRP for redundancy and if this is the case then you need to reserve the number of L3 devices + an extra IP for the virtual IP eg.

If ,for example, you have 2 L3 switches/routers for inter vlan routing and you were running HSRP between them you would need a total of 3 IP addresses one for each device and one for the virtual IP.

Jon

235
Views
0
Helpful
3
Replies
CreatePlease login to create content