Date: Wed, 28 Nov 2001 17:08:15 -0800 From: "Crist J. Clark" <cristjc@earthlink.net> To: "irado@nettaxi.com" <irado@nettaxi.com> Cc: freebsd-net@FreeBSD.ORG Subject: Re: netmask for aliased ip Message-ID: <20011128170815.G3985@blossom.cjclark.org> In-Reply-To: <200111281637.fASGbgd07767@mail2.bigmailbox.com>; from irado@nettaxi.com on Wed, Nov 28, 2001 at 08:37:42AM -0800 References: <200111281637.fASGbgd07767@mail2.bigmailbox.com>
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On Wed, Nov 28, 2001 at 08:37:42AM -0800, irado@nettaxi.com wrote:
>
> somebody told me that, when aliasing, the 2nd to īnī ipaddress netmask must not be the regular one, but 0xffffffff instead. Example:
>
> rl0 = 200.200.200.200 netmask 255.255.0.0
> rl0:0 (the aliased) 200.200.220.200 netmask 0xffffffff
> [lots more]
> rl0:3000 200.200.255.200 netmask 0xffffffff
>
> is it for real?? what is the reason for this?
Somebody told you wrong. When adding an alias _which is on the same
logical network_ as other addresses, it should have an 0xffffffff
mask. That is, only one address on an interface should have the "real"
netmask for any one network.
The simple explanation for this is that if you have,
a.b.c.d/24
a.b.c.e/24
On an interface and you try to initiate a connection to another
machine through this interface, should your connection use a.b.c.d or
a.b.c.e as the source address? It is ambiguous and can make problems.
In your case, the addresses lie on different networks. Each address
should have the netmask of the network it is on. Note that you do not
have the above problem in this case.
--
Crist J. Clark | cjclark@alum.mit.edu
| cjclark@jhu.edu
http://people.freebsd.org/~cjc/ | cjc@freebsd.org
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