Subject: Re: Why netmask 255.255.255.255 is needed for PPP
To: Matthias Scheler <tron@lyssa.owl.de>
From: Neil J. McRae <neil@domino.org>
List: current-users
Date: 11/22/1996 17:35:23
On 22 Nov 1996 11:39:35 +0100 
 tron@lyssa.owl.de (Matthias Scheler) wrote:

> 	Hi,
> 
> I recently send a PR about "pppd" not accepting netmask 255.255.255.255.
> As a result I got some mails saying me that netmasks are irrelevant for
> PPP connections - I believed that too before I discovered this problem -
> or that netmask 255.255.255.255 for an interface is always wrong.

Netmasks are relevent for PPP. Or anyother form of IP networking.

> 
> Here is the prove that I'm right.
> 
> tron@jehova:~#uname -a
> NetBSD jehova 1.1 NetBSD 1.1 (JEHOVA) #2: Tue May 21 23:03:27 MET DST 1996   
  tron@colwyn:/usr/src/sys/arch/i386/compile/JEHOVA i386
> 
> Here are the two interfaces involved in the problem:
> 
> tron@jehova:~#ifconfig ed0
> ed0: flags=8863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST>
>         inet 194.121.202.132 netmask 0xfffffff8 broadcast 194.121.202.135
> tron@jehova:~#ifconfig ppp0
> ppp0: flags=51<UP,POINTOPOINT,RUNNING>
>         inet 194.121.202.132 --> 194.121.202.185 netmask 0xfffffff8 
> 
> Now I try to add a route to a host on the same ethernet as the router:
> 
> tron@jehova:~#route add -net 194.121.202.208 -netmask 255.255.255.248 194.121
.202.130
> add net 194.121.202.208: gateway 194.121.202.130
> tron@jehova:~#traceroute 194.121.202.209
> traceroute to 194.121.202.209 (194.121.202.209), 30 hops max, 40 byte packets
>  1  colwyn.owl.de (194.121.202.185)  286.063 ms  250.02 ms  189.952 ms
>  2  jehova.owl.de (194.121.202.132)  219.295 ms  205.348 ms  200.316 ms
>  3  colwyn.owl.de (194.121.202.185)  308.69 ms  404.338 ms  320.49 ms
>  4  jehova.owl.de (194.121.202.132)  349.48 ms  385.297 ms  329.886 ms
> ^C
> 
> And as everybody can see it gets routed to the wrong destination. Ok,
> time to fix the netmask ...:
> 
> tron@jehova:~#route delete 194.121.202.208
> delete host 194.121.202.208
> tron@jehova:~#ifconfig ppp0 netmask 255.255.255.255
> 
> ... and to retry to add the route:
> 
> tron@jehova:~#route add -net 194.121.202.208 -netmask 255.255.255.248 194.121
.202.130
> add net 194.121.202.208: gateway 194.121.202.130
> tron@jehova:~#traceroute 194.121.202.209
> traceroute to 194.121.202.209 (194.121.202.209), 30 hops max, 40 byte packets
>  1  gaia.owl.de (194.121.202.130)  11.572 ms  2.481 ms  5.183 ms
>  2  beansidhe.owl.de (194.121.202.209)  137.896 ms  169.374 ms  159.967 ms
> 
> Wow, what a surprise: it worked.
> 
> Any doubts left that netmask 255.255.255.255 *is* required?
> 
This means unumbered interfaces, in such a case then yes this is requiened.

Neil
--
Neil J. McRae. Alive and Kicking.       Domino: In the glow of the night.
neil@DOMINO.ORG        NetBSD/sparc: 100% SpF (Solaris protection Factor) 
  Free the daemon in your computer!