Subnetting where called-for host ranges abut network ranges

So, this is more of a "what do they expect" question than anything...

In CCNA curriculum twice now I've seen examples where in IPv4 subnetting, the question asked for a given network to be broken into a number of hosts that basically completely matches the number of valid IP addresses in a given subnet. For example, asking for 30 hosts, asking for 14 hosts, the like. In the examples in the curriculum there was no accounting for the router itself needing an IP address, which would further reduce the available hosts by one.

For the purposes of assessment, should one assume that one does not need to leave space for the router on a given network when the number of hosts to build a network for matches the entire size of the usable range of addresses?

It seems to me in the real world that one absolutely would account for three unusable addresses in a given subnet in the form of the network address, the broadcast address, and the address used on the network routing equipment, such that the hosts would refer to the devices that make use of the network, as that's the actual goal.

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Comments

pevangel

You mentioned that hosts would refer to devices that make use of the network. With that definition, why wouldn't a router be considered a host?

Think of host as any device that connects to the network. A host could be a desktop, laptop, printer, AP, router, switch, etc.

TWX

pevangel wrote: »

You mentioned that hosts would refer to devices that make use of the network. With that definition, why wouldn't a router be considered a host?

Think of host as any device that connects to the network. A host could be a desktop, laptop, printer, AP, router, switch, etc.

You are correct, that a router, as a network device, is also a host. I suppose that's why they use 14-host and 30-host examples, since from a very literal point of view it qualifies. It's just funny that from the end-user perspective they don't care about how the network functions so long as they can do what they need to do; they don't care about the infrastructure, only about the function of the end-user devices.

My main reason for asking was simply to confirm.

shortstop20

Any IPs that might in the future be used by a router or other networking devices are to be included in the "usable host addresses".

You should disregard the number of networking devices on a subnet when calculating the total number of usable host addresses on said subnet.

TWX

I have had a problem with overthinking things at times, usually like this, when it's a fairly simple question that has ramifications that don't need to be delved into at this juncture.

This works well with human-administered and human-graded tests where the grader has latitude and can accept conditions that carry the answer further than the simple answer would, but obviously that does not work so well on computer-graded tests.