Use of network and broadcast ip addresses as node ip address

anis

Dear All,

I have a 192.168.1.0/24 network. I have broken down the network into 32 networks. Therefore, for each network I am loosing two IP addresses (broadcast and network) for each network. I heard there are ways to use this two IP address as node IP addressees.

My point is:

1. Is there any technique to do so? How?

2. If I implement the technique of using this two IP addresses, how will I be able to differentiate these 32 networks. (My target is to use maximum IP addresses and yet going on with my plan of using this 32 networks as 32 separate vlans)


Thank you

srg

I you're using this networks as pure pointtopoint networks i guess you could use /31-masks instead. That way you get two host ips, and no broadcast or network.

cambei

The only way *I know* of is of more use when you are assigned a block of IPs from an ISP. For example, if your ISP assigned at /29 for your use, you would only have 6 IPs available for hosts + router. However, if you use a subnet mask that is large enough and your hosts do not need to contact the IPs in the subnets either side of your range, then the network and broadcast can be used.

E.g:

Assigned range from ISP: 80.98.23.40 /29
Normal usable IPs: 80.98.23.41 - 80.98.23.46 (one assigned to router)

Set all hosts involved to use a subnet mask of 255.255.255.224 or a /27 and you will then be able to use the network and the broadcast addresses too. However, communication to any of the other addresses that falls into the 80.98.23.32/27 range will be broken as it will not leave your network.

This is a nasty hack and is technically breaking the rule of IP networks I suppose, but it can get you extra use of your public IPs.

Hope that made sense.

mcorline

If I have a network i.e 192.168.1.0/29, and all usable ip address are assigned, would it be possible to create a separate subnet e.g 192.168.1.0/32 and 192.168.1.7/32 to assign to hosts?

mcorline

Furthermore ^, on a firewall

powmia

You can absolutely use a /31 (255.255.255.254) subnet mask. Since they are point to point links, there's no need to use a broadcast (there's only one other possible host from any router's perspective)... and one host uses the network ID as their IP address. So the first link out of your network would use the host addresses of .0 and .1 for their point-to-point link. Keep in mind, not all vendor equipment will support this. For Cisco, some platforms will only allow you to do this on a true point-to-point link (ie, serial), some will let you do this on an ethernet link (broadcast type), but give you a warning... some will just let you do it.