use of non-contiguous masks in address lookups ?

[Aleksandr A Babaylov]

On Thu, May 24, 2012 at 02:07:11PM +0200, Luigi Rizzo wrote:
> On Thu, May 24, 2012 at 11:19:54AM +0000, Bjoern A. Zeeb wrote:
> > 
> > On 24. May 2012, at 07:43 , sthaug at nethelp.no wrote:
> > 
> > >> every now and then the issue comes up on whether we still need
> > >> to support non-contiguous masks in address lookups.
> > >> I seem to remember someone (perhaps on this list) making a
> > >> case for their presence, but forgot the details.
> > >> So, does anyone know of a practical use of non contiguous masks ?
> > > 
> > > I vote for removing non-contiguous masks. They are incompatible with
> > > CIDR, which was introduced in 1993 (!).
> > > 
> > > Non-contiguous masks have been unsupported in many routers produced
> > > the last 10 years or so.
> > 
> > Contrary I still know people using them and relying on it.  Not sure on
> > which version they are.
> > 
> > I am not quite sure what micro-optimizations on legacy IP will help
> > us after a decade or longer.  Let it rest and die gracefully the next
> > years.  Of course, fixing bugs still considered good:)
> 
> the point of my question was to get [f]actual usage information on non
> contiguous masks, because i don't know of any (at least on ipv4,
> maybe in ipv6 there is one). The answer does not have to affect
> FreeBSD, if that is what worries you.

Load balansing:

#netstat -rnfinet | sed -Ee 's|([ .])[1-9][0-9][.]|\1XX.|' -e 's|([ .])[1-9][0-9][0-9][.]|\1XXX.|' | head -8
Routing tables

Internet:
Destination        Gateway            Flags    Refs      Use  Netif Expire
0.0.0.0&0x101      XX.XXX.222.58      UGS         0     1241  vlan9
0.0.0.1&0x101      XXX.XX.246.254     UGS         0     1387  vlan1
0.0.1.0&0x101      XXX.XX.246.254     UGS         0     1568  vlan1
0.0.1.1&0x101      XX.XXX.222.58      UGS         0     1491  vlan9