On Tue, 30 Sep 2008, Brian Dickson wrote:
Dunn, Jeffrey H. wrote:
My basic question is: What basic engineering problem is solved by
proscribing non-64 bit prefixes?
If the non-64 prefixes had not been proscribed, we wouldn't have been
able to use the existing engineering method to develop CGA/SEND
specifications. These are being leveraged in SHIM6 and potentially in
other applications as well. Likely we couldn't even solve these
engineering problems (at least without major drawbacks/other
assumptions) if we couldn't have made assumptions about the
widely-used prefix length.
That said, I personally use non-64 bit prefixes on point-to-point
links between routers, but I have done so willingly and knowing that
if the IETF develops anything fancy new stuff, I might not be able to
use it or I might need to renumber.
When managing such a scheme alongside an IPv6 prefix which needs to
be assigned to the same set of servers, which are all dual-stack,
the *number* of prefixes, their *relative* numbering, and the host
*addresses* within the prefixes, it is quickly apparent that use of
only /64 prefixes makes for a management nightmare, particularly if
renumbering of prefixes and/or servers occurs, e.g. re-balancing the
VLSM arrangement itself in IPv4-land.
I don't understand why *relative* numbering (i.e: overlapping subnet
masks) is important in IPv6, and I'm not sure if I see the case even
for v4. Could you enlighten me?
I assume you refer to a scenario where on the same broadcast domain
there are hosts which are configured with say A.B.C.0/24 length, and
some others are configured with, say, A.B.C.D/28 prefix length.
--
Pekka Savola "You each name yourselves king, yet the
Netcore Oy kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
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