Subject: [rrg] solution strategies, nat?

From: "William Herrin" <[email-masked]>
Date: Wed, 31 Dec 2008 11:57:21 -0500

On Wed, Dec 31, 2008 at 11:07 AM, RJ Atkinson <[email-masked]> wrote:
> I agree with Steve Blake that a NAT-oriented approach,
> which I gather is category "H", ought to get serious consideration.

Ran,

Would you care to describe a NAT category which credibly addresses the
routing scalability problem in a manner not already encompassed in
widely deployed NAT systems?

I have no intention of adding:

Strategy H: We should use NAT!
Major criticisms: We should use NAT to do what exactly?

Regards,
Bill Herrin

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From: Steven Blake <[email-masked]>
Date: Wed, 31 Dec 2008 13:05:24 -0500

> widely deployed NAT systems?

That's the point: widely deployed NAT (as it exists today) is a
do-nothing strategy from an interdomain routing point-of-view.

> Major criticisms: We should use NAT to do what exactly?

Allow sites to have stable internal addressing without putting pressure
on interdomain routing scalability from additional PA prefixes.

PROS: 

- Unilateral deployment incentives: no need for any global
  coordination, or involvement by the providers.

- Widely tested, mature technology (for IPv4, at least).

CONS:

- Does not provide session survivability in the event of uplink failover
  (at least not with current IPv4/IPv6 and transport protocols).

- N:1 address multiplexing (v4 NAT) makes it difficult to support
  inbound connections.  v6 NAT could be better in this respect.

- Breaks certain classes of applications (i.e., those that depend on
  address referrals).  In some environments this is considered a
  feature, not a bug.

All of these cons could be mitigated by evolution of IP and/or transport
protocols.  As long as these enhancements support backwards
compatibility, they could be incrementally deployed.  Many have already
been discussed in RRG.

PS. Nobody despises NAT more than I do.

Regards,

// Steve

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From: "William Herrin" <[email-masked]>
Date: Wed, 31 Dec 2008 14:11:59 -0500

> do-nothing strategy from an interdomain routing point-of-view.

Steven,

I fail to see the point in describing more than one version of "do
nothing." If you insist that NAT needs mention, I would be willing to
alter the stragey F description to:

Strategy F.

Do nothing. (RFC 1887 § 4.4.1). The gains already achieved via CIDR
and NAT are sufficient to keep BGP stable for the foreseeable future.

Regards,
Bill Herrin

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From: RJ Atkinson <[email-masked]>
Date: Wed, 31 Dec 2008 14:37:07 -0500

> Ran,

1) It seems odd that you ask me particularly, and haven't
asked any of the other folks' whose comments I simply echoed. :-)

> widely deployed NAT systems?

2) Why rule out existing widely deployed NAT systems ?
    Who cares whether a cat is black or white, so long as it caches  
mice ?

> Major criticisms: We should use NAT to do what exactly?

3) This has been talked about within RRG before, but in summary:

(NAT/NAPT or LocatorRewriting or pick a another name) performed
inside a site's border router can enable a site to multi-home
effectively without any de-aggregation (i.e. without any impact
on the DFZ RIB or DFZ FIB).  Existing mechanisms that enable
distributed firewalls to share session state would clearly also
work to share NAT session state among a set of site border routers,
if that were desired.

I know of several sites that use this today with IPv4 and that are
happy with it.  Those users' main concern is with the absence of
"Architected NAT" -- that is an open specification so they can obtain
the same capabilities from multiple router suppliers.  This concept
also has been discussed at the BEHAVE WG list (and I'm told also
during several BEHAVE WG meetings in MSP).  There is even an I-D
on "NAT66" that seems relevant.

Cheers,

Ran

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From: "William Herrin" <[email-masked]>
Date: Wed, 31 Dec 2008 20:15:32 -0500

On Wed, Dec 31, 2008 at 2:37 PM, RJ Atkinson <[email-masked]> wrote:
>   Who cares whether a cat is black or white, so long as it caches mice ?

Ran,

Let me back up and explain:

Chris Vogt proposed a symmetric NAT which translates globally unique
end-user addresses in to and out of topologically aggregated core
network addresses, reducing the demand for core routing slots. His
approach, which he called "Six/One Router," is reflected in strategy
A4e.

I would like to hear about additional NAT-based techniques which, like
Chris' notion, suggest a credible plan for reducing the demand for
core routing slots compared to the status quo.

I would prefer not to hear about the usefulness of vanilla NAT. We
have determined beyond the shadow of a doubt that the status quo is
not, at this time, self-reducing. Vanilla NAT is indeed useful, but as
widely deployed today it is already a part of the status quo.

Regards,
Bill Herrin