Subject: RE: Stupid NAT tricks and how to stop them.

From: "Michel Py" <[email-masked]>
Date: Thu, 30 Mar 2006 20:35:13 -0800

> Noel Chiappa wrote:
> If you think there aren't still stability issues, why don't
> you try getting rid of all the BGP dampening stuff, then?
> Have any major ISP's out there done that?

Dampening is part of the protocol and has nothing to do with the speed
of light. Removing it is akin to removing packet re-ordering in TCP;
nobody with half a brain would consider it. Same as packets arriving out
of sequence, stability issues are part of life for someone who actually
operates a network. Code has bugs, hardware fails, power goes bezerk,
UPS batteries leak, rodents chew on cables, backhoes cut fiber, fat
fingers screw up configs, and rookies flap routes because they know
everything about astrophysics and nothing about running a production
network. That's what dampening is for.

> Stephen Sprunk wrote:
> Of course, they don't actually enforce this unless a user's
> upstream bandwidth usage consistently exceeds total POP
> upstream bandwidth divided by the number of users at the POP
> (in my case, about 300kB/s). Go above that and you get an email
> asking you to turn down the speed on your P2P client ;-)

Some bigger ISPs (with large POPs) prefer to limit the upstream so they
don't have to manage quotas/bandwidth. I have 512kb upstream; it's not
big but I can bittorrent all of it all day long, they don't care and
probably don't know.

> Alas, I've been unable to find a consumer-grade router that
> will run native IPv6, 6to4, or even pass through IPinIP

There's no market for it. Consumers don't know what it is and geeks
already have a hack or an el-cheapo-ebay Cisco. Heck, my home router is
a 7204 why would I go for a Linksys :-D

Michel.

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From: "Christian Huitema" <[email-masked]>
Date: Thu, 30 Mar 2006 21:12:25 -0800

> of light. 

Well, not really. Assume a simplistic model of the Internet with M
"core" routers (in the default free zone) and N "leaf" AS, i.e. networks
that have their own non-aggregated prefix. Now, assume that each of the
leaf AS has a "routing event" with a basic frequency, F. Without
dampening, each core router would see each of these events with that
same frequency, F. Each router would thus see O(N*F) events per second.
Since events imply some overhead in processing, message passing, etc,
one can assume that at any given point in time there is a limit to what
a router can swallow. In either N or F is too large, the router is
cooked. Hence dampening at a rate D, so that N*F/D remains lower than
the acceptable limit.

Bottom line, you can only increase the number of routes if you are ready
to dampen more aggressively. There is an obvious "tragedy of the
commons" here: if more network want to "multi-home" and be declared in
the core, then more aggressive dampening will be required, and each of
the "multi-homed" networks will suffer from less precise routing, longer
time to correct outages, etc.

There are different elements at play that also limit the number of core
routers. Basically, an event in a core router affects all the path that
go through it, which depending on the structure of the graph is
somewhere between O(M*log(M)) or O(M.log(M)). In short, the routing load
grows much faster than linearly with the number of core routers.

-- Christian Huitema

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From: Francois Menard <[email-masked]>
Date: Fri, 31 Mar 2006 07:04:34 -0500 (EST)

Does that constraint remains if peering happens closer to the edge to AS 
that are more regional in nature.  For instance, say the FCC mandated 
peering at the LATA level over IP-based IMT's/Bill'n'Keep trunks.

This is not far fetched, say that the PSTN transitions to SIP and say that 
peering on a bill and keep basis must extend to video conferencing in IP 
and not only to voice, then once the bill and keep is IP, it makes sense 
to run the rest of the IP traffic there, including the P2P traffic 
transitioning through regional AS.

So my thought is that we can enable MH, but if we keep it regional and 
then we do not have to worry about dampening lobotomized to handle 
load of O(N*F)

F.

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