Re: WG action: 1 week to discuss LL18: Host

> From: "Mika Liljeberg" <[email protected]>
> I agree. In fact, I would like to see something along these lines as
> close to the top as possible. The fact that the specification doesn't
> properly consider multihoming should be made clear from the beginning.
> That should save implementors some considerable anxiety.

Here is an attempt to remove some of the ambiguity and be more explicit
about the multi-homing issues.

Replace all of section 2.6.2 with:

>>>
2.6.2.  Forwarding Rules

If a host is multihomed, then it must first determine which interface to use
to send any packet, whether or not the destination is a Link-local address.
This specification does not define how this decision is made.  Rather, the
issues are explained and advice is given on how to address known problems
(see Section 3).

Whichever interface is used, if the destination address is in the 169.254/16
prefix (including the 169.254.255.255 broadcast address), then the sender
MUST ARP for the destination address and then send its packet directly to
the destination on the same physical link.  This MUST be done whether the
interface is configured with a Link-local or a routable IPv4 address.

In many network stacks, achieving this functionality may be as simple as
adding a routing table entry indicating that 169.254/16 is directly
reachable on the local link.

The host MUST NOT send a packet with a Link-Local IPv4 destination
address to any router for forwarding.

If the destination address is a unicast address outside the 169.254/16
prefix, then the host SHOULD use an appropriate routable IPv4 source
address, if it can. If for any reason the host chooses to send the packet
with a Link-Local source address (e.g. no routable address is available on
the selected interface), then it MUST ARP for the destination address and
then send its packet, with a Link-Local IPv4 source address and a routable
destination IPv4 address, directly to its destination on the same physical
link. The host MUST NOT send the packet to any router for forwarding.
>>>


Note that the option of dropping the packet is covered by the host not
"choosing to send the packet..." and therefore the MUST is appropriate.

Philip