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Date:      Thu, 29 Nov 2001 18:01:04 +0500
From:      "Ahsan Ali" <ahsan@khi.comsats.net.pk>
To:        <freebsd-net@FreeBSD.ORG>
Subject:   Re: netmask for aliased ip
Message-ID:  <001301c178da$90108550$0100a8c0@ahsanalikh>
References:  <200111281637.fASGbgd07767@mail2.bigmailbox.com> <20011128170815.G3985@blossom.cjclark.org> <002d01c1788c$8388f4f0$be026b83@ahsanali> <20011128222900.L3985@blossom.cjclark.org>

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> 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...


My point is, that if the aliased interface also had a class c mask, this
issue wouldn't have come up in the first place when considering local
(within the same subnet) access from other hosts on that network.

I know this sounds really obfusticating! :)

But I'm just trying to get my concepts sorted out too.

-Ahsan



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