Re: Scalability issues in the Internet routing system

[JORDI PALET MARTINEZ <jordi.palet () consulintel es>]

I think that to be "technically correct" is appropriate to say that we can
have almost 2^64 networks (having reserved space doesn't mean that we can't
use it in the future), and each network can accommodate up to 2^64 nodes.
But is also true that it seems difficult in reality to reach that number of
nodes.

So it is so much inaccurate to say that IPv4 has 2^32 addresses than to say
that IPv4 has 2^128, even if theoretically both figures are correct, because
practical issues.

Regards,
Jordi




> De: "Rubens Kuhl Jr." <rubensk () gmail com>
> Responder a: <owner-nanog () merit edu>
> Fecha: Thu, 27 Oct 2005 00:04:58 -0200
> Para: James <james () towardex com>
> CC: Lincoln Dale <ltd () interlink com au>, <nanog () nanog org>
> Asunto: Re: Scalability issues in the Internet routing system
>
>
> > > IPv6 will someday account for as many IPv4 networks as would exist
> > > then, and IPv6 prefixes are twice as large as IPv4 (64 bits prefix vs
> > > 32 bits prefix+address, remainder 64 bits addresses on IPv6 are
> > > strictly local), so despite a 3x cost increase (1 32 bit table for
> > > IPv4, 2 for IPv6) on memory structures and 2x increase on lookup
> > > engine(2 engines would be used for IPv6, one for IPv4), the same
> > > techonology that can run IPv4 can do IPv6 at the same speed. As this
> > > is not a usual demand today, even hardware routers limit the
> > > forwarding table to the sum of IPv4 and IPv6 prefixes, and forward
> > > IPv6 at half the rate of IPv4.
> >
> > s/64/128/
> >
> > ...and total, complete, non-sense.  please educate yourself more on reality
> > of inet6 unicast forwarding before speculating.  Thank you.
>
> From RFC 3513(Internet Protocol Version 6 (IPv6) Addressing Architecture):
>   "For all unicast addresses, except those that start with binary value
>    000, Interface IDs are required to be 64 bits long and to be
>    constructed in Modified EUI-64 format."
>
> If Interface ID is 64 bits large, prefix would be 64 bits max,
> wouldn't it ? Usually it will be somewhere between 32 bits and 64
> bits.
>
> As for 000 addresses:
>
> "  Unassigned (see Note 1 below)         0000 0000      1/256
>    Unassigned                            0000 0001      1/256
>    Reserved for NSAP Allocation          0000 001       1/128 [RFC1888]
>    Unassigned                            0000 01        1/64
>    Unassigned                            0000 1         1/32
>    Unassigned                            0001           1/16
>
>   1. The "unspecified address", the "loopback address", and the IPv6
>       Addresses with Embedded IPv4 Addresses are assigned out of the
>       0000 0000 binary prefix space.
> "
>
> Embedded IPv4 can be forwarded using IPv4 lookup, and all other 000
> cases can be handled in slow-path as exceptions. IANA assignment
> starts at 001 and shouldn't get to any of the 000 sections.
>
> One interesting note though is Pekka Savola's RFC3627:
> "Even though having prefix length longer than /64 is forbidden by
>    [ADDRARCH] section 2.4 for non-000/3 unicast prefixes, using /127
>    prefix length has gained a lot of operational popularity;"
>
> Are you arguing in the popularity sense ? Is RFC 3513 that apart from
> reality ? An October 2005(this month) article I
> found(http://www.usipv6.com/6sense/2005/oct/05.htm) says "Just as a
> reminder, IPv6 uses a 128-bit address, and current IPv6 unicast
> addressing uses the first 64 bits of this to actually describe the
> location of a node, with the remaining 64 bits being used as an
> endpoint identifier, not used for routing.", same as RFC 3513.
>
> Limiting prefix length to 64 bits is a good thing; it would be even
> better to guarantee that prefixes are always 32 bits or longer, in
> order to use exact match search on the first 32 bits of the address,
> and longest prefix match only on the remaining 32 bits of the prefix
> identifier.
>
>
> Rubens




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