[CentOS] Two small issues after upgrade to 4.2 -- [OT] IPv4 LINKLOCAL

Scot L. Harris webid at cfl.rr.com
Mon Oct 24 21:55:10 UTC 2005

On Mon, 2005-10-24 at 17:14, Bryan J. Smith wrote:
> "Scot L. Harris" <webid at cfl.rr.com> wrote:
> > zeroconf is what puts the route in your routing
> > table.  Look at netstat -rn to see it.
> > Suppose to allow you to turn on a system without setting up
> > any networking and the system is suppose to find other
> > systems and self configure themselves into a network.  You
> > can disable zeroconf by modifying /etc/sysconfig/network by
> > setting the following:
> >   nozeroconf = yes
> > (again that may be in all caps, check the file)
> > Have never seen this used for anything.  And don't expect
> > to see it used any time soon.
> Actually, the 169.254./16 network is IPv4 LINKLOCAL.
> It is the IPv4 equivalent to FE80::/10, IPv6 LINKLOCAL.
> I haven't kept up with various standardizations, it's not
> only perfect normal to have both a 169.254./16 and another
> IPv4 address on an interface, but it is encouraged for some
> scenarios.  In other words, do not be bothered by the
> existance of a 169.254./16 address on a IPv4 dynamically
> assigned interface.
> This will be such the case with IPv6.  All IPv6 nodes have a
> LINKLOCAL address of FE80::/10, as well as another.  The
> initial IPv6 design was to allow up to 3 -- LINKLOCAL
> (FE80::/10), SITELOCAL (FEC0::/10) and then a public, but
> SITELOCAL has been recently deprecated (even if not
> official).
> The lower half/16-bit (two 8-bit octets) of the IPv4
> LINKLOCAL are generated from the 48-bit MAC address of the
> interface.  In IPv6 LINKLOCAL, it is the lower half/64-bit
> (four 16-bit words), which easily handles the full 48-bit MAC
> address.

If you disable zeroconf the 169.254 entry is dropped.  What use is it? 
Nothing I have found explains what it is used for or why I need it on my
systems.  Waving your hands and saying don't be bothered by the
existence of such entries does not explain what it is used for.  Getting
rid of it does not impact the systems either.  Kind of like an appendix.

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