v6 & DSL / Cable modems [was: Private use of non-RFC1918 IP space

Roger Marquis marquis at roble.com
Thu Feb 5 03:05:22 UTC 2009

Mark Andrews wrote:
> 	All IPv6 address assignments are leases.  Whether you get
> 	the address from a RIR, LIR or ISP.  The lease may not be
> 	renewed when it next falls due.  You may get assigned a
> 	different set of addresses at that point.  You should plan
> 	accordingly.

Exactly the problem, and the reason A) IPv6 is not and will not be a viable
option any time soon (soon being before the publication of an IPv6 NAT
RFC), and B) why network providers (and other parties who stand to gain
financially) are firmly against IPv6 NAT.

>  If we could get a true accounting of the extra cost imposed
>  by NAT's I would say it would be in the trillions of dollars.

This is exactly the sort of hyperbole, like RFC4864's proposing that
application-layer proxies are a viable substitute for NAT, that discredits
IPv6 proponents.  Those who remember the financial industry's push for SET,
a failed encryption technology, will be struck by the similarities in
technical vs rhetorical arguments.

Perhaps what we need is an IPv6 NAT FAQ?  I'm suspect many junior network
engineers will be interested in the rational behind statements like:

  * NAT disadvantage #1: it costs a lot of money to do NAT (compared to what
  it saves consumers, ILECs, or ISPs?)

  * NAT disadvantage #2 (re: your IPv6 address space) Owned by an ISP?  It
  isn't much different than it is now.  (say again?)

  * NAT disadvantage #3: RFC1918 was created because people were afraid of
  running out of addresses. (in 1992?)

  * NAT disadvantage #4: It requires more renumbering to join conflicting
  RFC1918 subnets than would IPv6 to change ISPs. (got stats?)

  * NAT disadvantage #5: it provides no real security. (even if it were true
  this could not, logically, be a disadvantage)

OTOH, the claimed advantages of NAT do seem to hold water somewhat better:

  * NAT advantage #1: it protects consumers from vendor (network provider)

  * NAT advantage #2: it protects consumers from add-on fees for addresses
  space. (ISPs and ARIN, APNIC, ...)

  * NAT advantage #3: it prevents upstreams from limiting consumers'
  internal address space. (will anyone need more than a /48, to be asked in

  * NAT advantage #4: it requires new (and old) protocols to adhere to the
  ISO seven layer model.

  * NAT advantage #5: it does not require replacement security measures to
  protect against netscans, portscans, broadcasts (particularly microsoft
  netbios), and other malicious inbound traffic.

Roger Marquis

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