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.

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?

-- 
Matthias Scheler
tron@lyssa.owl.de