Date: Thu, 30 Jun 2011 00:14:12 +0300 From: Oleg Cherevko <olwi@icyb.kiev.ua> To: "Li, Qing" <qing.li@bluecoat.com> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: ifconfig alias: same subnet netmask question Message-ID: <4E0B95A4.3020207@icyb.kiev.ua> In-Reply-To: <4E0B5DB1.5090702@fb-n.l.org.ua> References: <4E0B406D.8070406@fb-n.l.org.ua> <B143A8975061C446AD5E29742C531723098B9C@PWSVL-EXCMBX-01.internal.cacheflow.com> <4E0B5DB1.5090702@fb-n.l.org.ua>
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Darn, I have to correct myself once again. Oleg Cherevko wrote: > 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). The above two prefixes should read "(192.168.1.0/24 and 192.168.1.2/32)", of course. > > 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). This one should read "(192.168.1.0/24)" as well. > 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 Or manpage text is simply outdated?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-net@freebsd.org [mailto:owner-freebsd- >>> net@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 >>> _______________________________________________ >>> freebsd-net@freebsd.org mailing list >>> http://lists.freebsd.org/mailman/listinfo/freebsd-net >>> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" > > -- Olwi
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