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From: j@uriah.heep.sax.de (J Wunsch)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: User PPP
Date: 1 Jun 1997 09:52:37 GMT
Organization: Private BSD site, Dresden
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Message-ID: <5mrgp5$40h@uriah.heep.sax.de>
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Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:42002
Eivind Eklund <perhaps@yes.no> wrote:
> I've worked with netmasks from 22 to 29 bits - 8 addresses, 64
> addresses, 256 addresses, 1024 addresses. They exists, and just about
> everything support it. A lot of things don't support non-continuous
> netmasks, though - FreeBSD included.
Non-conti*g*uous, btw. FreeBSD supports non-contiguous netmasks.
First, let's create an interface with a weird netmask:
uriah # ifconfig vx0 192.168.1.1 netmask 0xffffff0f
Install a rejected default route, so `route get' will output something
useful below.
uriah # route -n add 0.0.0.0 127.0.0.1 -reject
add net 0.0.0.0: gateway 127.0.0.1
This is clearly a case for the default route:
uriah # route -n get 192.168.2.1
route to: 192.168.2.1
destination: default
mask: default
gateway: 127.0.0.1
interface: lo0
flags: <UP,GATEWAY,REJECT,DONE,STATIC,PRCLONING>
recvpipe sendpipe ssthresh rtt,msec rttvar hopcount mtu expire
49152 49152 0 0 0 0 16384 0
...correct. Now, all hosts with 192.168.1.X are in our network if
(X & 0x0f) == 1. .17 should be there:
uriah # route -n get 192.168.1.17
route to: 192.168.1.17
destination: 192.168.1.1
mask: 255.255.255.15
interface: vx0
flags: <UP,DONE,CLONING>
recvpipe sendpipe ssthresh rtt,msec rttvar hopcount mtu expire
0 0 0 0 0 0 1500 -67
...as well as .33:
uriah # route -n get 192.168.1.33
route to: 192.168.1.33
destination: 192.168.1.1
mask: 255.255.255.15
interface: vx0
flags: <UP,DONE,CLONING>
recvpipe sendpipe ssthresh rtt,msec rttvar hopcount mtu expire
0 0 0 0 0 0 1500 -83
...but .34 is another network ((34 & 0x0f) == 2):
uriah # route -n get 192.168.1.34
route to: 192.168.1.34
destination: default
mask: default
gateway: 127.0.0.1
interface: lo0
flags: <UP,GATEWAY,REJECT,DONE,STATIC,PRCLONING>
recvpipe sendpipe ssthresh rtt,msec rttvar hopcount mtu expire
49152 49152 0 0 0 0 16384 0
As you can see, it works well. Of course, the netstat -r output looks a
little funny now:
uriah # netstat -rn
Routing tables
Internet:
Destination Gateway Flags Refs Use Netif Expire
default 127.0.0.1 UGRSc 0 0 lo0
127.0.0.1 127.0.0.1 UH 6 5313 lo0
192.168.1.1&0xffffff0f link#1 UC 0 0
--
cheers, J"org
joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)