Li, Qing wrote:
First of all, are you encountering any issues ?
Well, for the last 14+ years I used to setup aliases with 0xffffffff netmask and
everything worked OK. However recently I encountered situation where
0xffffffff-style alias triggered some unwanted network behavior.
When one sets alias like this:
ifconfig em0 inet 192.168.1.1 netmask 0xffffff00
ifconfig em0 inet 192.168.1.2 netmask 0xffffffff alias
and then exports connected networks via OSPF ASE, two prefixes end up being
exported (192.168.1.1/24 and 192.168.1.2/32).
In case of "identical netmask" setup:
ifconfig em0 inet 192.168.1.1 netmask 0xffffff00
ifconfig em0 inet 192.168.1.2 netmask 0xffffff00 alias
only one prefix gets exported (192.168.1.1/24).
In my particular situation two exported prefixes led to wrong behavior of some
equipment (other than FreeBSD machine in question). When I changed to "identical
netmask" setup (one exported prefix) everything started to work flawlessly.
So far I encountered no issues with this "identical netmask" setup.
So I'd like to know why ifconfig manpage still recommends old way of setting
aliases? Perhaps there are some pitfalls that I'm not aware of? Or manpage text
is simply outdated?
There is an outstanding issue with the address alias and improper routing
table update that I am actively working on.
--Qing
-----Original Message-----
From: owner-freebsd-...@freebsd.org [mailto:owner-freebsd-
n...@freebsd.org] On Behalf Of Oleg Cherevko
Sent: Wednesday, June 29, 2011 8:11 AM
To: freebsd-net@freebsd.org
Subject: ifconfig alias: same subnet netmask question
Hi All,
When describing the "alias" parameter ifconfig manpage claims that "If
the address is on the same subnet as the first network address for this
interface, a non-conflicting netmask must be given. Usually 0xffffffff
is most appropriate."
Taking into account that FreeBSD supports aliases from the same subnet
with identical netmask for 6+ years now, does this statement still make
sense? And what does this "conflicting netmask" stand for (I mean in
the
context of more or less recent FreeBSD versions, say 8.0+)?
Are there any drawbacks in setting aliases like this:
ifconfig em0 inet 192.168.1.1 netmask 0xffffff00
ifconfig em0 inet 192.168.1.2 netmask 0xffffff00
instead of traditional:
ifconfig em0 inet 192.168.1.1 netmask 0xffffff00
ifconfig em0 inet 192.168.1.2 netmask 0xffffffff
(again, for more or less recent FreeBSD versions)?
--
Olwi
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--
Olwi
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