Date: Tue, 4 Mar 2008 01:52:46 -0800 From: Jeremy Chadwick <koitsu@freebsd.org> To: "Chris H." <chris#@1command.com> Cc: freebsd-stable@freebsd.org, Edwin Groothuis <edwin@mavetju.org>, Mark Andrews <Mark_Andrews@isc.org>, Andy Dills <andy@xecu.net> Subject: Re: What's new on the 127.0.0/24 block in 7? Message-ID: <20080304095246.GA77655@eos.sc1.parodius.com> In-Reply-To: <20080304000320.msp5bfrytc0wsowg@webmail.1command.com> References: <200803040619.m246Jbja018523@drugs.dv.isc.org> <20080304000320.msp5bfrytc0wsowg@webmail.1command.com>
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On Tue, Mar 04, 2008 at 12:03:20AM -0800, Chris H. wrote:
> I have absolutely no idea why FBSD v7 (on 2 machines) will only
> dole out 127.0.0.1, while all my other servers running RELENG_6 all
> dole out a /minimum/ of 127.0.0.1/8 by default. But, having just now
> modified the default rc for ifconfig_lo0 to a 255.255.255.0 netmask
> now makes a different response when querying rbldnsd.
Okay, let's back up here.
The reason your FreeBSD machines don't respond on addresses other than
127.0.0.1 is because your lo0 interface does not have 127.0.0.2 and
127.0.0.3 addresses bound to them. These are called IP aliases. To add
them, do the following:
# ifconfig lo0 inet 127.0.0.2 netmask 255.255.255.255 alias
# ifconfig lo0 inet 127.0.0.3 netmask 255.255.255.255 alias
The netmask specified on an alias line is important! Use what I showed;
do not argue. And yes, Linux does it differently.
To make this work on bootup, add the following to rc.conf:
ifconfig_lo0_alias0="inet 127.0.0.2 netmask 255.255.255.255"
ifconfig_lo0_alias1="inet 127.0.0.3 netmask 255.255.255.255"
You do not need an "ifconfig_lo0" line in /etc/rc.conf; there is already
one in /etc/defaults/rc.conf which will be used correctly.
Secondly, on both RELENG_6 and RELENG_7, when the 127.0.0.1 address is
assigned to lo0, the netmask used is 255.0.0.0. Evidence:
$ uname -r
6.3-PRERELEASE
$ grep lo0 /etc/rc.conf
$ grep lo0 /etc/defaults/rc.conf
ifconfig_lo0="inet 127.0.0.1" # default loopback device configuration.
#ifconfig_lo0_alias0="inet 127.0.0.254 netmask 0xffffffff" # Sample alias entry.
$ ifconfig lo0
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
inet 127.0.0.1 netmask 0xff000000
$ uname -r
7.0-STABLE
$ grep lo0 /etc/rc.conf
$ grep lo0 /etc/defaults/rc.conf
ifconfig_lo0="inet 127.0.0.1" # default loopback device configuration.
#ifconfig_lo0_alias0="inet 127.0.0.254 netmask 0xffffffff" # Sample alias entry.
$ ifconfig lo0
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
inet 127.0.0.1 netmask 0xff000000
Thirdly, it's pretty apparent you don't understand what a netmask does.
Machines don't "dole out 127.0.0.1/8" -- this phrase makes no sense.
A netmask is what defines a region of IP address space in which a
machine within said region will honour packets within. More
specifically: it tells the machine "for any IP address you have bound to
this interface, respond to packets destined to the broadcast address of
that network region".
For example, if you had a network region of 192.168.1.0/24 (in English,
the region would be 192.168.1.0 to 192.168.1.255), your broadcast
address would be 192.168.1.255. Your network address is 192.168.1.0,
but that's for another discussion.
If you put a machine on that network as 192.168.1.200, and give it a
netmask of 255.255.255.0, it will respond to any packets destined to
192.168.1.100 (obviously), but will also respond to packets destined to
the broadcast address (192.168.1.255).
If you then put another box on the network as 192.168.1.7, and give it a
netmask of 255.255.255.128 (/25), it should not be able to see
192.168.1.200. Broadcast packets from 192.168.1.7 would be going to
192.168.1.128 (its "view" of the network would be 192.168.1.0 to
192.168.1.128).
This is a completely different beast than IP aliasing, but hopefully my
explanation helps regardless.
--
| 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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