IPv6 network boundaries vs. IPv4

Kevin Oberman oberman at es.net
Mon Aug 27 01:01:35 UTC 2007

> Date: Sat, 25 Aug 2007 23:56:29 -0600
> From: John Osmon <josmon at rigozsaurus.com>
> Sender: owner-nanog at merit.edu
> Is anyone out there setting up routing boundaries differently for
> IPv4 and IPv6?  I'm setting up a network where it seems to make
> sense to route IPv4, while bridging IPv6 -- but I can be talked
> out of it rather easily.
> Years ago, I worked on a academic network where we had a mix
> of IPX, DECnet, Appletalk, and IP(v4).  Not all of the routers
> actually routed each protocol -- DECnet wasn't routable, and I recall
> some routers that routed IPX, while bridging IP...

DECnet not routable? Not even close to true. At one time DECnet was
technically well ahead of IP networking and far more commonly used. It
was not until about 1993 that IP traffic passed DECnet as the dominate
protocol and ESnet continued to route DECnet, mostly to support the High
Energy Physics community. When the Hinsdale fire segmented tie IP
Internet in 1988, the global DECnet Internet survived, albeit with limits
bandwidth between the coasts.

DECnet was far from perfect and, over time, IP surpassed it in terms of
both performance and robustness, but it was not only routable, but
globally routed long ago.

> This all made sense at the time -- there were IPX networks that needed
> to be split, while IP didn't need to be.  DECnet was... DECnet -- and 
> Appletalk was chatty, but useful. 

AppleTalk was a royal pain! Gator boxes and FastPaths would go insane
and saturate the network with broadcasts. But AppleTalk did have some
really neat features.

> I keep hearing the mantra in my head of: "I want my routers to route, and 
> my switches to switch."  I agree wholeheartedly if there is only one 
> protocol -- but with the mix of IPv4 and IPv6, are there any folks
> doing things differently?  With a new protocol in the mix are the
> lessons of the last 10 (or so) years not as clear-cut?

Most routers are a blend of router and switch. The Cisco 6500 and 7600
boxes are probably the most popular large router in the world, but the
heart of each is a Catalyst switch. So, the switch switches and the
router routes, but they are both the same box.

At a major networking show we would switch the IPv6 back to the core
routers because of bugs in the IPv6 implementations on many systems.

You do what works best for your network. If it means switching IPv6, so
be it. This is probably especially true when the router is from a
company that charges substantially extra for IPv6 software licenses. If
the is only limited IPv6 traffic, switching to a central router might
not only be technically the best solution, but the most reasonable
fiscal approach.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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