Date: Tue, 13 Feb 2007 13:32:19 -0800 From: Jeremy Chadwick <koitsu@FreeBSD.org> To: freebsd-stable@FreeBSD.ORG, fcash@ocis.net Subject: Re: Desired behaviour of "ifconfig -alias" Message-ID: <20070213213219.GA72359@icarus.home.lan> In-Reply-To: <200702132036.l1DKaP0f022622@lurza.secnetix.de> References: <200702131055.41407.fcash@ocis.net> <200702132036.l1DKaP0f022622@lurza.secnetix.de>
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On Tue, Feb 13, 2007 at 09:36:25PM +0100, Oliver Fromme wrote: > > > # ifconfig re0 > > > re0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 > > > options=1b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING> > > > inet 88.198.44.136 netmask 0xffffffe0 broadcast 88.198.44.159 > > > inet 88.198.173.154 netmask 0xfffffff8 broadcast 88.198.173.159 > > > inet 88.198.173.155 netmask 0xfffffff8 broadcast 88.198.173.159 > > > inet 88.198.173.156 netmask 0xfffffff8 broadcast 88.198.173.159 > > > inet 88.198.173.157 netmask 0xfffffff8 broadcast 88.198.173.159 > > > inet 88.198.173.158 netmask 0xfffffff8 broadcast 88.198.173.159 > > > > > > > In that situation, wouldn't deleting the primary IP > > > > cause connection issues for the rest of the IPs? > > > > > > No. I can delete _any_ of the above IP addresses, and the > > > others would still work perfectly fine. I already did > > > things like that (on a different machine). > > > > Yes, but each of the IPs is on their own subnet. > > No, please look closer. The addresses above are all in the > same subnet (except for the first one). It's a /29 subnet > in this case, but it works exactly the same with /24 or any > other subnet masks. Your configuration looks incorrect. How or why it's working is proof that the implementation (read: source code) differs from what some of the docs state. My guess is that it's working because you already have AFAIK, it should be (note alias entries 2,3,4): ifconfig_re0="inet 88.198.44.136 netmask 255.255.255.240" ifconfig_re0_alias0="inet 88.198.173.154 netmask 255.255.255.248" ifconfig_re0_alias1="inet 88.198.173.155 netmask 255.255.255.255" ifconfig_re0_alias2="inet 88.198.173.156 netmask 255.255.255.255" ifconfig_re0_alias3="inet 88.198.173.157 netmask 255.255.255.255" ifconfig_re0_alias4="inet 88.198.173.158 netmask 255.255.255.255" My guess is that it's working because your routing table already has an entry for 88.198.173.154/29 which was created by the first entry. The remaining aliases on that network (88.198.173.154/29) utilise that, but should really have netmasks with all 1s. ifconfig(8) states you should use 255.255.255.255/0xffffffff (all 1s) for IP aliases. The FreeBSD Handbook documents everything I've said quite clearly: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/configtuning-virtual-hosts.html > As I said, I would have to try that because I haven't used > the /32 netmask hack for quite some time. I think it would > indeed use the first address, i.e. x.x.x.2. As far as I know it's not a hack. If it is/was a hack, can you explain the functional difference between IP aliases with a 0xffffffff netmask vs. mixed-set-bits, and point to some past references stating the difference? -- | Jeremy Chadwick jdc at parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB |
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