On 1/19/2015 8:48 AM, Alexandru Petrescu wrote:
Brian,
Le 16/01/2015 20:16, Brian E Carpenter a écrit :
Alex,
but to improve the layers below IP such as to have IP run
unmodified.
In the general case that is impossible, because the SDO that
develops the lower layer isn't interested. If the lower layer is
intrinsically NBMA then for sure ARP or ND+DAD will not work as
designed. If the lower layer doesn't support a physical MTU of at
least 1280 IPv6 will not work as designed. So in the general case
both an adaptation layer and an NBMA solution are required. And as
you know, there are other "Ethernet" assumptions that don't apply in
a low-power wireless scenario.
Of course the goal is "IP over Everything" but that isn't the same
as "Everything must be like Ethernet", which you seem to imply.
In fact when you read draft-baccelli-manet-multihop-communication
(and imagine what its security section will say when it's been
written), I think the conclusion is that a great many things have to
change, not in the IP packet format, but in the ecosystem currently
provided by ARP/DHCP or RA/ND/DAD/SLAAC/DHCPv6.
In a sense I agree.
Adapting these IP protocols to these links (instead of improving MAC or
adaptation layers) seem to bring it Middle Boxes, break bidirectional
reachability from across globe, break security, hurt IP packet
analyzers, and more.
But certainly yes there are (1) some parameters in these IP protocols
(timers, preference values and (2) some protocol options (unsolicited
NA) which, when tweaked, make IP run better on these links.
And some additional mechanisms that can be used here just as they have
been other NBMA subnets, which already address the protocol issues above.
If IP has broader issues because of the persistent need for these
mechanisms, then they should be dealt with. But so far I haven't heard
anything sufficiently new for this environment to drive that discussion.
Joe
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