Stupid Question maybe?

Wed Dec 19 18:17:27 UTC 2018

On 19/12/2018 16:24, Naslund, Steve wrote:

> It has ALWAYS been the only correct way to configure equipment and is
> a requirement under CIDR.  Here were your commonly used netmasks
> before CIDR/VLSM :
> 
> 255.0.0.0 255.255.0.0 255.255.255.0
> 
> Which one is not contiguous?

There is an example in RFC950 on page 15.

    3.  A Class C Network Case (illustrating non-contiguous subnet bits)

       For this case, assume that the requesting host is on class C
       network 192.1.127.0, has address 192.1.127.19, that there is a
       gateway at 192.1.127.50, and that on network an 3-bit subnet field
       is in use (01011000), that is, the address mask is 255.255.255.88.

Admittedly, page 6 contains:

       Since the bits that identify the subnet are specified by a
       bitmask, they need not be adjacent in the address.  However, we
       recommend that the subnet bits be contiguous and located as the
       most significant bits of the local address.

I have never seen noncontiguous network masks used in real life, but I 
may not be old enough.

-- 
Adam Atkinson