Stupid Question maybe?

Wed Dec 19 20:28:36 UTC 2018

On Wed, Dec 19, 2018 at 12:12 PM Thomas Bellman <bellman at nsc.liu.se> wrote:
> On 2018-12-19 20:47 MET, valdis.kletnieks at vt.edu wrote:
> > There was indeed a fairly long stretch of time (until the CIDR RFC came out and
> > specifically said it wasn't at all canon) where we didn't have an RFC that
> > specifically said that netmask bits had to be contiguous.
>
> How did routers select the best (most specific) route for an address?
> If the routing table held both (e.g.) 10.20.30.0/255.255.255.64 and
> 10.20.30.0/255.255.255.32, then 10.20.30.97 would match both, and have
> the same number of matching bits.

Easy: .97 matches neither one because 64 & 97 !=0 and 32 & 97 != 0.
That's a 0 that has to match at the end of the 10.20.30.

The problem is 10.20.30.1 matches both, so which one takes precedence?
Can't have a most-specific match when two matching routes have the
same specificity.

I'm guessing the answer was: the routing protocols didn't accept
netmasks in the first place and you were a fool to intentionally
create overlapping static routes.

Regards,
Bill

-- 
William Herrin ................ herrin at dirtside.com  bill at herrin.us
Dirtside Systems ......... Web: <http://www.dirtside.com/>