Re: [v6ops] Routers are hosts too!

[Mark Smith <[e-mail]>]

On 9 January 2016 at 02:24, Alexandre Petrescu
<[e-mail]> wrote:
>
>
> Le 08/01/2016 15:35, Jeff McAdams a écrit :
>>
>>

>>
>> So what's your point?
>
>
> Maybe we should find that small rounding error - what OS does not implement
> longest-match and yet connects to the Internet?
>
> Second, until we ifnd that small rounding error, we may stop talking about
> Hosts, and declare the Host RFC historic.  Or update it with a sentence
> saying that Hosts too must implement longest-match.
>

So I think that might be missing the fundamental point I was making.

The distinction between a host and a router is a functional one,
purely related to what a device does when it receives a packet with a
non-local address, rather than being an fixed attribute of a
particular box of electronics. For example, a box of electronics
having multiple physical interfaces doesn't always make it a router,
or a box of electronics that only has a single physical interface
doesn't always make it a host.

I think the simple question to ask to determine whether the device is
performing a host or a router function for a particular packet is
"does the destination address in the packet match one of the receiving
device's addresses?". If the destination address does, then the packet
has reached its final destination, and the receiving device is a host
and will process the complete packet.

Another question to answer (which is more or less a rephrasing of the
previous question), is "where is the packet payload care/don't care
boundary?" If the device doesn't care what the packet payload is, it
is a forwarding device i.e. a router. If the device does care what the
payload is, because it is going to be processing the payload, then it
is a host, and that means that the packet has reached the destination
indicated in the destination address field. In the end-to-end
argument, it is the ends that are processing payloads.

A more specific version of that question is "does payload encryption
matter to the device or not?". If payload encryption doesn't matter,
then the device is a forwarding device/router, if payload encryption
does matter, meaning that the receiving device needs to be in a
position to decrypt the payload, then the device is a host, and the
destination address in the packet matches one of the host's addresses.

Regards,
Mark.