Subject: Re: Interface specification in route(8)
To: None <,>
From: Ignatios Souvatzis <>
List: tech-net
Date: 02/23/1999 12:54:55
On Tue, Feb 23, 1999 at 01:32:07PM +0200, Lucio de Re wrote:
> According to Ignatios Souvatzis:
> > 
> > I dont know why a ppp should _ever_ have a netmask (other than
> >
> > 
> is the traditional value for a numbered point-to-point 
> link.  Or are you saying that _this_ is a bad idea?  I think you may 
> have a point if you do, but perhaps you can expand on it?

IP version 4 point to point links, be it PPP or SLIP, be it 4.3BSD or 4.4BSD
derived systems, semantically do not create a network of their own.

They have a local address and a remote address.

The kernel routes by looking wether the single remote address matches, when
it finds an interface with the POINTTOPOINT bit on.

This is 99% of a real unnumbered interface: you can share the IP address of
your Ethernet as your local address.

I dont know exactly what happens when you ifconfig (or the ioctl pppd does)
a POINTTOPOINT interface to a non-FFFFFFFF netmask. Apparently, it creates
a routing table entry with that netmask, which lateron causes trouble. I've
witnessed this all the time since I took over the PPP FAQ. Just dont do it.