Add ARP to INET or require ND6

[Roy Marples]

Hi List

While adding the IN_IFF_TENTATIVE functionality and friends it was pointed out
that ARP is optional with INET.
The argument at the time being why pay for ARP if there are no real
interfaces?

However, NS/NA (the ARP equivalent of IPv6) is not optional with INET6, it's
forced.

So the burning question is this:
Should we turn NS/NA into an option or remove the ARP option?

I'm in favour of the latter as I would find it hard to test patches for the
former given my restricted hardware set.

Roy

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[Mouse]

Post by Roy Marples
While adding the IN_IFF_TENTATIVE functionality and friends it was
pointed out that ARP is optional with INET.
The argument at the time being why pay for ARP if there are no real
interfaces?

Seems to me it's more "why pay for ARP if there are no ARP-using
interfaces?", but perhaps that's what "real" actually means there.
(There are plenty of ways to transport IP packets that don't need ARP,
starting with PPP.)

Post by Roy Marples
However, NS/NA (the ARP equivalent of IPv6) is not optional with
INET6, it's forced.
Should we turn NS/NA into an option or remove the ARP option?

I'd argue in favour of the former.

Post by Roy Marples
I'm in favour of the latter as I would find it hard to test patches
for the former given my restricted hardware set.

I don't think "I can't test option 1" is a good driver for technical
decisions. I'd prefer to make it an option, comment in the config
files that INET6 without NS/NA is untested beyond making sure it
builds, with the comment to be removed if/when it gets tested.

Of course, I'm not the one doing the work.

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[John Nemeth]

On May 4, 6:34pm, Mouse wrote:
}
} > While adding the IN_IFF_TENTATIVE functionality and friends it was
} > pointed out that ARP is optional with INET.
} > The argument at the time being why pay for ARP if there are no real
} > interfaces?
}
} Seems to me it's more "why pay for ARP if there are no ARP-using
} interfaces?", but perhaps that's what "real" actually means there.
} (There are plenty of ways to transport IP packets that don't need ARP,
} starting with PPP.)
}
} > However, NS/NA (the ARP equivalent of IPv6) is not optional with
} > INET6, it's forced.
}
} > So the burning question is this:
} > Should we turn NS/NA into an option or remove the ARP option?
}
} I'd argue in favour of the former.

The mistake here, which is one made by many people, is in
thinking of IPv6 as IPv4 with larger addresses. It's not, it is
a distinct protocol. So, I would argue for doing neither. IPv4
is not IPv6. NS/NA is integral to IPv6; ARP is not integral to
IPv4.

} > I'm in favour of the latter as I would find it hard to test patches
} > for the former given my restricted hardware set.
}
} I don't think "I can't test option 1" is a good driver for technical

I have to agree. This would set an extremely bad precedence.

} decisions. I'd prefer to make it an option, comment in the config
} files that INET6 without NS/NA is untested beyond making sure it
} builds, with the comment to be removed if/when it gets tested.

As NS/NA is integral to IPv6, this would be a silly thing to do.

}-- End of excerpt from Mouse

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[Robert Elz]

Date: Mon, 04 May 2015 23:12:59 +0100
From: Roy Marples <***@marples.name>
Message-ID: <***@uberpc.marples.name>

| The argument at the time being why pay for ARP if there are no real
| interfaces?

Not really, ARP was an add-on to IPv4, it didn't originally exist, and
only (strictly) applies to ethernet interfaces - other interface types
have their own address resolution protocols. Many of them are (not
coincidentally) essentially identical to ARP, but they are all distinct,
and could potentially diverge over time.

On the other hand, ND is a fundamental part of IPv6, and applies in the
exact same way to all interface types (ie: the interface is irrelevant).

The two are really barely comparable, other than both providing similar
services.

There's no need to change anything, leave ARP as it is (optional, even
if almost no-one ever disables it) and ND included with all the rest of v6.

kre



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