The stupidity of trying to "fix" DHCPv6

Ray Soucy rps at maine.edu
Thu Jun 16 13:24:28 CDT 2011


The beauty of Ethernet is that it's simple.  "Ethernet" has evolved
considerably, and continues to do so.  It's not really fair to make
comments about it's sociability and talk about it as if it were still
in the state it was 20 years ago:

"Ethernet doesn't scale because of collisions and exponential backoff"

We got around large collision domains by replacing hubs with switches,
effectively shrinking the collision domain to the link between the
host and the switch (and only in half-duplex).

"Ethernet doesn't scale because of large amounts of broadcast traffic."

We started to introduce multicast, and multicast-aware switches in
IPv4; in IPv6 there is no broadcast traffic.  We won't be able to
scale networks up until we can turn off IPv4, but once we can IPv6
will be able to grow much larger in terms of per-LAN.   The best
practice of no more than 512 per broadcast domain will seem very
outdated at that point; especially when you add in multicast flood
protection, the available bandwidth goes up, and performance of
network interfaces improves.

The link you pointed to is talking about flat networks of tens of
thousands of hosts; that might be excessive right now...  But I can
certainly see an IPv6-only LAN (with some filtering to make sure ARP
and IPv4 traffic is dropped at the port) scaling easily to thousands
of hosts with today's hardware.

I know the post is a little off topic; but as someone who's met
Metcalfe several times I think it's only fair to not make Ethernet out
to be the only thing preventing scaleability of networks.

On Wed, Jun 15, 2011 at 1:04 PM,  <sthaug at nethelp.no> wrote:
>> > Ethernet is not designed for huge LANs. If you want that you need
>> > to make significant changes - http://www.cl.cam.ac.uk/~mas90/MOOSE/
>>
>> Hm:
>>
>> "Our object is to design a communication system which can grow smoothly to accommodate several buildings full of personal computers and the facilities needed for their support."
>>
>> Ethernet: Distributed Packet Switching for Local Computer Networks
>> Robert M. Metcalfe and David R. Boggs
>> Communications of the ACM Volume 19 Issue 7, July 1976
>
> So let's change it slightly: Ethernet is not designed for huge
> broadcast domains.
>
> How big is huge? To some degree it depends on how broadcast "chatty"
> the protocols used are - but there's also the matter of having a
> size which makes it possible to troubleshoot. Personally I'd prefer
> an upper limit of a few hundred computers.
>
> Steinar Haug, Nethelp consulting, sthaug at nethelp.no
>
>
>



-- 
Ray Soucy

Epic Communications Specialist

Phone: +1 (207) 561-3526

Networkmaine, a Unit of the University of Maine System
http://www.networkmaine.net/




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