FreeBSD eats 169.254.x.x addressed packets

[Peter C. Lai]

On 2010-06-08 11:44:29AM -0700, Jeremy Chadwick wrote:
> On Tue, Jun 08, 2010 at 02:26:10PM -0400, Stephen Clark wrote:
> > On 06/08/2010 02:05 PM, Jeremy Chadwick wrote:
> > >On Tue, Jun 08, 2010 at 01:45:59PM -0400, Stephen Clark wrote:
> > >>Why does FreeBSD 6.3 eat 169.254.x.x addressed packet when
> > >>4.9 didn't?
> > >
> > >The following output would help:
> > >
> > >- ifconfig -a
> > >- netstat -rn
> > >- Contents of /etc/rc.conf
> > >
> > >Also, be aware that RELENG_6 is to be EOL'd at the end of this year:
> > >http://security.freebsd.org/
> > >
> > Hi Jeremy,
> > 
> > I am not sure that information is relevant. We have two systems configured
> > identically one using 4.9 the other 6.3.
> 
> My concern was that someone had botched something up in rc.conf or
> during the OS upgrade/migration, resulting in there being no loopback
> interface.  I also wanted to verify that your routing table looked
> correct for what ifconfig showed.
> 
> Other users pointed you to RFC 3927.  Wikipedia has this to say:
> 
> http://en.wikipedia.org/wiki/Link-local_address
> 
> "Based on RFC 3927, IPv4 uses the 169.254.0.0/16 range of addresses.
> However, the first and last /24 subnet (256 addresses each) in this
> block have been excluded from use and are reserved by the standard.[1]"
> 
> I read this to mean 169.254.0.0/24 and 169.254.255.0/24.
> 
> Your previous ifconfig statement shows:
> 
> > $ ifconfig rl0
> > rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
> >         options=8<VLAN_MTU>
> >         inet 192.168.129.1 netmask 0xffffff00 broadcast 192.168.129.255
> >         inet 169.254.1.1 netmask 0xffff0000 broadcast 169.254.255.255
> >         ether 00:30:18:ae:7c:77
> >         media: Ethernet autoselect (100baseTX <full-duplex>)
> >         status: active
> 
> With this configuration, you're using both the first and last /24
> netblocks -- 169.254.0.0 for your network address, and 169.254.255.255
> for your broadcast address.
> 
> You should be able to avoid this by using 169.254.1.0/24.
> 

RFC 3927 also has complicated rules involving when one can or should not
use a link-local address on the same interface as a routable IP, so at
best your configuration may not be supported anyway. One should not use
a link-local address as if it were under RFC 1918 rules, in particular
because link-local involves self-assigned addresses and internal
conflict mitigation.

-- 
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Peter C. Lai                 | Bard College at Simon's Rock
Systems Administrator        | 84 Alford Rd.
Information Technology Svcs. | Gt. Barrington, MA 01230 USA
peter AT simons-rock.edu     | (413) 528-7428
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