[505] in linux-net channel archive
Re: CONFIG_INET_SNARL: What for?
daemon@ATHENA.MIT.EDU (Matthias Urlichs)
Thu Jun 15 02:20:31 1995
To: submit-linux-dev-net@ratatosk.yggdrasil.com
From: urlichs@smurf.noris.de (Matthias Urlichs)
Date: 15 Jun 1995 07:32:10 +0200
In linux.dev.net, article <9506141309.aa00659@cs.nrl.navy.mil>,
Craig Metz <cmetz@sundance.itd.nrl.navy.mil> writes:
>
> >It still doesn't work, because in the future blocks will be assigned from
> >"class A" space.
>
> Is this postulation, assumption, or known fact?
>
Nobody knows. Net 39 is an experiment to find out if this would work. The
idea is to grab Class A addresses and split them up into smaller chunks,
which would prolong the useful life of IPv4 for quite some time. In fact,
almost all of the remaining Class A networks are already reserved for this.
Read the latest RFCs if you want to know more.
> But this is somewhat irrelevant, anyway. The whole concept of a
> single-homed host knowing what networks are "at your site" or not is FUBAR.
>
Unfortunately, that's correct.
> >You cannot tell the size of the block from the address. ifconfig knows
> >the correct netmask and that's what should be used.
>
> The interface table holds the correct netmask for all of your direct
> attach interfaces. This may be obtained from ifconfig, BOOTP, DHCP, or ICMP
> subnet mask advertisements. This has no correlation in a subnetted environment
> to your site's classed or CIDR address block.
>
The netmask and the MTU to the destination can be stored in the routing
entry. Until somebody puth Path MTU Discovery in, that's the correct place
to store it. IMHO, the SNARL hack is superfluous (you can as well add an
additional route to your default gateway with the desired MTU, for the
(non)local (sub)nets to which it would apply) and CONFIG_INET_SNARL should
at least default to N in arch/*/config.in.
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