Date: Thu, 29 Nov 2001 14:10:37 -0800 From: "Crist J. Clark" <cristjc@earthlink.net> To: Ahsan Ali <ahsan@khi.comsats.net.pk> Cc: freebsd-net@FreeBSD.ORG Subject: Re: netmask for aliased ip Message-ID: <20011129141037.F8815@blossom.cjclark.org> In-Reply-To: <001301c178da$90108550$0100a8c0@ahsanalikh>; from ahsan@khi.comsats.net.pk on Thu, Nov 29, 2001 at 06:01:04PM %2B0500 References: <200111281637.fASGbgd07767@mail2.bigmailbox.com> <20011128170815.G3985@blossom.cjclark.org> <002d01c1788c$8388f4f0$be026b83@ahsanali> <20011128222900.L3985@blossom.cjclark.org> <001301c178da$90108550$0100a8c0@ahsanalikh>
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On Thu, Nov 29, 2001 at 06:01:04PM +0500, Ahsan Ali wrote:
> > For TCP, that is what is always used by default when creating an
> > outbound connection. For incoming connections, the machine will of
> > course reply using the IP address the connection came in on. And a
> > program can always request to use a specific address if it wants to.
> >
> > I am not sure where you see a problem.
>
> What I am saying is that if you have (for instance) 192.168.0.0/24 as a
> network.
>
> Interface A has the IP 192.168.0.10 with a netmask of 255.255.255.0 (/24)
> Alias A:1 has the IP 192.168.0.11 with a netmask of 255.255.255.255 (/32)
>
> Now Host B (192.168.0.20 mask 255.255.255.0) tries to access Alias A:1 which
> is 192.168.0.11/32 so B sends to A:1 which it (correctly) assumes to be on
> its own network, Alias A:1 cannot however reach B without sending the data
> to its configured gateway. If routing is enabled on this host then it may be
> able to send the reply routed through Interface A only...
Hmmm? Routing is always enabled if you plan on talking to any other
machines at all. But all of this is a non-issue. The selection of a
route for a packet has _nothing_ to do with the source address, only
the destination. How a packet finds its way to 192.168.0.20 is the
same no matter what the source address is. 192.168.0.20 is local to
the interface A, so it is sent directly to B.
--
Crist J. Clark | cjclark@alum.mit.edu
| cjclark@jhu.edu
http://people.freebsd.org/~cjc/ | cjc@freebsd.org
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