On Wed, December 23, 2015 5:00 pm, Louis Lagendijk wrote:
On Wed, 2015-12-23 at 19:04 +0100, Patrick Bervoets wrote:
Op 23 dec. 2015 om 18:31 heeft Valeri Galtsev <galtsev@kicp.uchicag o.edu> het volgende geschreven:
If I understand IP networking correctly, you only can have "aliases" of the interface appear on the _same_ network segment (I'm tempted to say same class C network) as the main IP of interface, say you have:
DEVICE=eth0 IPADDR=x.y.z.w NETMASK=255.255.255.0 GATEWAY=x.y.z.254
Then with the restriction I mentioned you can have alias:
DEVICE=eth0:0 IPADDR=x.y.z.a NETMASK=255.255.255.255
Note that "x.y.z." part is the same in both IPs.
Somebody may correct me if I'm wrong.
Valeri
I have used an 10. Alias on a 192. Interface so it is possible Patrick
I believe you are right. A netmask of 255.255.255.255 however seems wrong. With that netmask a broadcast for address resolution will not work...
NETMASK=255.255.255.255 for alias interface serves very simple purpose. It allows to avoid processing of all broadcasts on particular segment of the network through alias interface as well. As main interface already does it, you don't want duplication of the same through alias interface. In general, if you make NETMASK=255.255.255.0 for alias, all should work (on Linux I'm sure it will, on FreeBSD you will get an error), but with this setting you do bizarre thing I described above. All these packets are sent to kernel, and the difference is in kernel network stack of Linux and FreeBSD, I figure.
Valeri
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++++++++++++++++++++++++++++++++++++++++ Valeri Galtsev Sr System Administrator Department of Astronomy and Astrophysics Kavli Institute for Cosmological Physics University of Chicago Phone: 773-702-4247 ++++++++++++++++++++++++++++++++++++++++