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From: brian@anorak.coverform.lan (Brian Somers)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Two devices with same IP
Date: 23 Nov 1996 22:46:47 -0000
Organization: Coverform Ltd.
Lines: 49
Sender: brian@awfulhak.demon.co.uk
Message-ID: <577usn$15g@anorak.coverform.lan>
References: <56ltqk$nhv@csugrad.cs.vt.edu> <56lvvc$62f$1@gail.ripco.com>
<574f3l$2s4@anorak.utell.net> <nigel.25.000F465B@znet.net.au>
Reply-To: brian%anorak.coverform.lan@awfulhak.demon.co.uk
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In article <nigel.25.000F465B@znet.net.au>,
nigel@znet.net.au (Nigel Gorry) writes:
>>In article <nigel.20.0000C75A@znet.net.au>,
>> nigel@znet.net.au (Nigel Gorry) writes:
>>:
>>: An ifconfig -a on my machine show that I have the same IP address for both my
>>: NIC and PPP interfaces. This works as a router with the default route being
>>: via the remote side of the PPP link.
>>:
>>: ed0: flags=8863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>>: inet 203.61.202.20 netmask 0xfffffff0 broadcast 203.61.202.31
>>: lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
>>: inet 127.0.0.1 netmask 0xff000000
>>: tun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1500
>>: inet 203.61.202.20 --> 203.61.202.1 netmask 0xffffff00
:
>>I don't get this. First, how come you're broadcasting on an address outside
>>of your network on ed0 ? ed0's netmask says that the allowable range is
>>203.61.202.{16-23} !
:
: I'm not - the subnet is 203.61.202.{16-31} netmask of 255.255.255.240
: (0xfffffff0)
I'll learn to count one day :)
>>If the above machine sends a packet to 203.61.202.{16-19,21-22} (assuming
>>that 203.61.202.16 is your net address and 203.61.202.23 is your *real*
>>broadcast address, how does your kernel know which of ed0 and tun0 to send
>>the packet ?
:
: because tun0 is a Point-to-Point link, so it will only send packets over tun0
: that are destined for the remote end.
:
: Therefore my routing table is such:
:
: 203.61.202.16/28 --> ed0
: 203.61.202.1 --> tun0
: default --> 203.61.202.1 (via tun0)
Ah, well that's my original point. Your tun0 device (IMO) should have
a netmask of 0xffffffff. A looser netmask says that I can reach
additional machines directly down that interface - which doesn't
really make sense down a point-to-point type interface.
--
Brian <brian%anorak.coverform.lan@awfulhak.demon.co.uk>
<http://www.awfulhak.demon.co.uk/>
Don't _EVER_ lose your sense of humour....
.