On Sun, Oct 28, 2018 at 08:18:44PM +0300, Reco wrote:
On Sun, Oct 28, 2018 at 12:56:13PM -0400, The Wanderer wrote:The definition for netmask I find in that section is netmask mask Netmask (dotted quad or CIDR) which at a glance would lead me to expect a full CIDR-format address (e.g., 192.168.1.1/24) here. That would clearly seem redundant with the address field immediately above, but I don't know of anything else that's consistent with CIDR notation.I agree that this part of the manpage is in dire need of good wording. I'd replace it with "Netmask (dotted quad or number of bits, eg 24)", because that's how it actually works.
Mostly the netmask field should be considered a legacy interface. Historically, the address was only the address, and the netmask was the dotted-quad formatted netmask for that address. When ifupdown gained the ability to specify the address field in address/bits format (in wheezy), the netmask field was extended to also recognize cidr bits in addition to dotted quad. (This also provides symmetry with the ipv6 representation, where dotted quad doesn't make sense.) With the new address syntax the netmask field is fully redundant, but remains for upgrades and compatibility with old scripts/etc.