Henrik:
Your point is well taken. However, there have historically been many
network stacks that are broken. Microsoft is responsible for a large
percentage of those. I can't remember WHEN windows IP stacks stopped
attempting to directly contact any address, rather than realizing that
the address in question was not directly connected, but I do remember
seeing that behavior. I've also seen lots of networks where there are
multiple subnets on the same broadcast LAN.
It's in keeping with the old tenet: "Be conservative in what you send,
and liberal in what you accept". I wasn't saying that it was a GOOD
idea, I was just explaining why it happens. In a correctly configured
network, if a node has forwarding enabled, it should reply to arps on
any address, and if it's not forwarding, it shouldn't. As you pointed
out, in a correctly configured network where all nodes have correctly
coded IP stacks, any other behavior isn't useful.
On Thu, 2004-11-25 at 01:00 +0100, Henrik Nordstrom wrote:
> On Wed, 24 Nov 2004, Lawrence MacIntyre wrote:
>
> > It's a routing optimization for the network. Even if your dual-homed
> > machine isn't a router, it's still on both segments. The alternative is
> > that the net has to route your packet to the other segment. It's
> > clearly more efficient to have the machine answer directly.
>
> Except that there will never be a ARP request for an IP which belongs to
> the other segment if your network is built correctly.
>
> The only meaningful use of this "ARP replying of all global addresses" I
> have found is to simplify IP "alias" management in certain situations by
> adding them to the loopback device rather than the real device when it is
> not known exactly which network segment the user/administrator intends the
> IP alias should be active within.
>
> Regards
> Henrik
--
Lawrence MacIntyre 865.574.8696 macintyrelp@xxxxxxxx
Oak Ridge National Laboratory
High Performance Information Infrastructure Technology Group
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