Subject: Re: [v6ops] Focused discussion: draft-gont-v6ops-ipv6-ehs-packet-drops

From: Nick Hilliard <[email-masked]>
Date: Mon, 01 Feb 2016 10:21:55 +0000

joel jaeggli wrote:
> Sometimes a slow forwarding path is not an option
> 
> e.g. the options are fast path or no path.

depends on the speed of the link.  For anything other than trivially
slow edge links, slow forwarding path is non-viable and represents a
serious denial of service vector.

Nick

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From: "Howard, Lee" <[email-masked]>
Date: Mon, 1 Feb 2016 13:02:03 +0000

>serious denial of service vector.

Well, I¹d say it depends on the available capacity of the CPU relative to
the speed of the link. I don¹t care if you¹re on a big router, if your
CPU¹s already at 90%, you can¹t slow-path an additional T1.

Lee

>
>Nick
>
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From: Nick Hilliard <[email-masked]>
Date: Mon, 01 Feb 2016 13:15:38 +0000

> CPU¹s already at 90%, you can¹t slow-path an additional T1.

If you're on a big router, there is no slow path.

Nick

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From: Nick Hilliard <[email-masked]>
Date: Mon, 01 Feb 2016 15:09:35 +0000

> If you're on a big router, there is no slow path.

Mikael Abrahamsson and I discussed this off-line.  Technically he was
correct to point out that there are slow paths available on some large
router models.  Conversely there are other routers models which don't
include a slow path of any form - i.e. packets which cannot be handled
in the normal data forwarding plane are blackholed.

Regardless of model, all packets which are punted on high performance
routers are rate limited to the point that it would be highly
inadvisable to depend on this as a viable packet forwarding mechanism,
which is why I said that there is no slow path: technically it exists in
some cases, but where it does, it is non-viable to the point that it is
better to assume that it doesn't exist in the first place.

Nick

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From: Ca By <[email-masked]>
Date: Mon, 1 Feb 2016 07:56:36 -0800

> better to assume that it doesn't exist in the first place.
+1

CB

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From: joel jaeggli <[email-masked]>
Date: Mon, 1 Feb 2016 09:55:14 -0800

On 2/1/16 7:56 AM, Ca By wrote:
> 
> 
> On Mon, Feb 1, 2016 at 7:09 AM, Nick Hilliard <[email-masked]
> <mailto:[email-masked]>> wrote:
> 
>     Nick Hilliard wrote:

If you have a rate limit for control traffic of all varieties at
~20-100kpps and asic based path of 14Bpps you're not using the former as
part of the forwarding path.  if you are a designer of said product,
you're not going to allow recourse to CPU forwarding for packets you
can't parse because that's a recipie for a meltdown.

>     [email-masked] <mailto:[email-masked]>

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From: Warren Kumari <[email-masked]>
Date: Mon, 01 Feb 2016 18:30:38 +0000

> can't parse because that's a recipie for a meltdown.

... and, even if the vendor might allow it, operators would want a way to
disable it.
I *so* don't want some monkey on the Internet sending me packets carefully
crafted to be punted into the slow path.

This means that vendors would need to build slow path forwarding, and lots
of tunable knobs to allow operators to choose which packets may take that,
and at what rate...

"A well-known scientist (some say it was Bertrand Russell) once gave a
public lecture on astronomy. He described how the earth orbits around the
sun and how the sun, in turn, orbits around the center of a vast collection
of stars called our galaxy. At the end of the lecture, a little old lady at
the back of the room got up and said: "What you have told us is rubbish.
The world is really a flat plate supported on the back of a giant
tortoise." The scientist gave a superior smile before replying, "What is
the tortoise standing on?" "You're very clever, young man, very clever,"
said the old lady. "But it's turtles all the way down!"
- Hawking, 1988

W