-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Wed, Feb 07, 2018 at 09:58:55PM +1100, Erik Christiansen wrote: > On 07.02.18 09:33, Michelle Konzack wrote:
[...] > > auto eth2 > > iface eth2 inet static > > address 192.168.4.12 > > netmask 255.255.127.0 > > gateway 192.168.4.1 > > network 192.168.4.0 > > > > So, it is not so good idea to leafe it out > > Michelle, that netmask is 0b11111111111111111000000100000000 , which is > the first I have ever seen with a hole in it. No, that would be 1111 1111 1111 1111 0111 1111 0000 0000 (some spacing added for legibility). But the "hole" thing still is there. I have no idea what network equipment will do on that. But at least the Linux networking stack keeps you from doing that: tomas@trotzki:~$ sudo ifconfig eth0 192.168.230.5 netmask 255.255.127.0 SIOCSIFNETMASK: Invalid argument Whereas: tomas@trotzki:~$ sudo ifconfig eth0 192.168.230.5 netmask 255.255.128.0 does work without complaints. (to the purists out there: I can't for the life of me remember what 'ip' wants me to chant to achieve that! I keep using both...) > For 512 addresses, I'd > have expected 255.255.254.0, which has contiguous bits: > 0b11111111111111111111111000000000 (If 10 bits (1024 addresses) were the > aim, then it would be 252, but never 127, if I have any kind of grip on > this stuff.) Yes. > Not trusting the software to handle an unusual netmask, I might have > been tempted to just use a class B netmask, 255.255.0.0 , but then I can > be a Feigling in such matters. CIDR should Just Work. But holes, OTOH... Cheers - -- t -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEUEARECAAYFAlp630YACgkQBcgs9XrR2kZK1QCXU0xUZAijiUknWjyvjZh7+RYJ cACfRXMkzEzgOQGUrBv8xMNX/iykhiY= =3NnL -----END PGP SIGNATURE-----
