IPv6 network boundaries vs. IPv4

Peter Dambier peter at peter-dambier.de
Sun Aug 26 09:06:21 UTC 2007

John Osmon wrote:
> 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...
> 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. 
> 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?

Hi John,

I remember old DECNET, DDCMP, IPX and NetBios days.
I used to have a couple of 19.2 kilobaud async lines, 2 arcnets and
an ethernet (thinwire technology but on RG13U cables, almost yellow wire
and UHF connectors - PL-259 like CB-radio).

DDCMP could route, IPX could and NetBios was riding on either IPX or
DDCMP so it did not matter.

Later the DDCMP async was replaced with a lots of switches and repeaters.
Whe used to have a backbone (yellow cable) connecting two VAXes and a
repeater that was feeding some 8 thinwires. Half of the thinwires were
feeding DECNET Terminalservers and PCs the other half were IPX with
a single one Netware server and lots of PCs.

In its best times the network was seeing some 1000 hosts. Everything
was running 10 MBit ethernet. there were 9 segments and no routers.

I have seen you could put some 30 NetBios PCs into a single segment
or more than 200 DECNET hosts if they were connected via switches and
thinwire transceivers.

Today without thinwire or yellow cable and with switches that can do
1 Gbit between switches and 100 Mbit to devices you should be able to
keep some 1000 hosts within a single switched network.

NAT-routers seem to have a limit of some 250 hosts within a single network.

I dont know if those boxes really can do 250 or if their MAC address
tables break even earlier. I have seen those boxes missbehave when
a bad ethernet adapter randomly changed its MAC address.

There are quite some link local things in IPv6 so it makes a lot of
sense to keep them within a single network - beside that nasty /64
habit that suggests forget radvd and automatic addresses but have
an IPv4 address of the 192.168... variety and use 6to4 adressing
for your local network.

I was running my own network, 4 IPv4 networks and 3 IPv6 networks
without routers, only switches :) the 6to4 trick helped me survive
but now I dont know if the IPv6 boxes were really seeing each other
other simply using 6to4 routes :)

Kind regards
Peter and Karin

Peter and Karin Dambier
Cesidian Root - Radice Cesidiana
Rimbacher Strasse 16
D-69509 Moerlenbach-Bonsweiher
+49(6209)795-816 (Telekom)
+49(6252)750-308 (VoIP: sipgate.de)
mail: peter at peter-dambier.de
mail: peter at echnaton.arl.pirates

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