Subnetting; lost address space??
Posted on 1998-06-17
We are creating some small local subnets from a local class-C address space; we really want the effect of a remote bridge, but this seems like the easiest way to do it. We use a pair of Linux boxes with PPP links connecting them, and have the local router proxy-ARP for the addresses on the small remote segment.
We allocated a small chunk of 8 addresses, (xxx.xxx.xxx.136-143, with netmask of xxx.xxx.xxx.248).
The claim made was that the parent space loses
I have read a possible concern with this (Linux IP-subnet mini-HowTo), and want clarification.
It states: once subnetted, the smallest subnet granularity of a network segment will determine wastage over the entire class-C, because the first/last address of every possible subnet of that size is now unavailable in the parent C-space.
This seems wrong to me. The subnetting is transparent to the host address space.
If there was a subnet declared in the main router to the host space, then perhaps this would be true.
If the sub-netting was known at the router entry to the C-space, instead of via proxy-ARP which hides it, then this could be an issue, but even then is this FAQ correct?
-- creating a small subnet for 8 remote devices would create 32*2=64 address holes in the C-space?
For the sake of this example, let us assume that you have decided to subnetwork you C class IP network number 192.168.1.0
into 4 subnets (each of 62 usable interface/host IP numbers). However, two of these subnets are being combined into a larger single network, giving three physical networks.
Network Broadcast Netmask Hosts
192.168.1.0 192.168.1.63 255.255.255.192 62
192.168.1.64 192.168.1.127 255.255.255.192 62
188.8.131.52 192.168.1.255 255.255.255.126 124 (see note)
Note: the reason the last network has only 124 usable network addresses (not 126 as would be expected from the network mask) is that it is really a 'super net' of two subnetworks. Hosts on the other two networks will interpret 192.168.1.192 as the network address of the 'non-existent' subnetwork. Similarly, they will interpret 192.168.1.191 as the broadcast address of the 'non-existent' subnetwork."
Is this a correct analysis?