Re: comments on mech-v2-01

["Chirayu Patel" <chirayu@chirayu.org>]

See below...

On Mon, 10 Nov 2003 16:13:28 +0100 (CET), "Erik Nordmark"
<Erik.Nordmark@sun.com> said:
> > 1) A race is triggered when an IPv6 router that has a configured
> >    tunnel with another router is doing dynamic mtu detection. The
> >    outcome of the race is that one or more ICMPv6 "packet too big"
> >    message might not be sent out to an host.
> >
> > Assume an IPv6 network like:
> >
> > [H1]-------->[R1]===========>[R2]--------->[H2]
>
> >   5. H1->R1 TCP packet of size 1400 (this is a retry)
> >   6. R1->H1 ICMPv6 "packet too big" with size 1300
> >   7. H1->R1 TCP packet of size 1400 (this is a retry)
> >   8. ... (the above cycle might repeat if there are more IPv4 routers
> >      that send ICMPv4 "fragmentation needed" with 8 bytes of payload)
>
> I don't understand how it can repeat. Do you think it can repeat
> forever?

No it will not repeat forever. That is why I used "might" in point 8.

> When the 8-byte payload ICMP errors are sent then R1 will effectively
> compute the minimum received (per IPv4 path MTU discovery).
>
> It is true that in the case of 8-byte payload ICMP errors you get at
> least two packet drops instead of at least one in the case of a single
> layer of MTU discovery (R1 needs to learn the tunnel MTU which causes
> at least one packet loss, and then H1 needs to learn the MTU from R1
> which causes at least one packet loss. (And in all cases there can be
> more than one packet loss if there are multiple large packets in flight
> at the same time.)

Your wording sums it up nicely. My thinking is that such a case is non-
obvious, and we should have a note about it in the draft.

> > 9) Link-layer address (which is an IPv4 address) is not meant to be
> >    used with ND. Is there any reason that the sending (of link-layer
> >    address) is a "SHOULD NOT", and the receiving is a ?MUST ignore?.
> >    The sending, and the receiving parts should be made consistent
> >    with respect to link- layer address. i.e. sending should be a
> >    "SHOULD NOT", and receiving should be a "SHOULD ignore?, or
> >    sending should be a "MUST NOT", and receiving should be a "MUST
> >    ignore?.
>
> The reason it was written like this was to not immediately invalidate
> any older implementations that might have sent the link-layer address
> options. I don't know if there ever were any such implementations.

Do you think we should change it now? I prefer "SHOULD NOT" and
"SHOULD ignore".

CP