Tom,
On 22/2/21 11:55, Tom Herbert wrote:
On Sun, Feb 21, 2021 at 2:39 AM Fernando Gont <fgont@xxxxxxxxxxxxxxx> wrote:
Hello, Tom,
On 20/2/21 12:32, Tom Herbert wrote:
[...]
[....]
This is reflected in the statement: "If an IPv6 header chain is
sufficiently long that it exceeds the packet look-up capacity of the
router, the router might be unable to determine how the packet should
be handled, and thus could resort to dropping the packet." It's not to
me clear what "sufficiently long" means; in particular, such a
statement isn't helpful to the host stack developer trying to figure
out if the packets they're creating will be properly forwarded.
"Long enough" for the router handling the packet. There are different
vendors, and different models. S the specific value will vary across
router vendors and models. In our document, we reference two sample
values -- but they are certainly not the only ones.
Fernando,
Yes, different routers do different things, but can you quantify what
the most commonly deployed routers do?
That's not what this document is about.
If we can do that then we could
establish a better requirement for host stacks more than just "don't
send IPv6 header chains that are too long".
This document intentionally focuses on elaborating on the underlying
problem, and *not* on providing such a recommendation. We can certainly
embark ourselves on that project once we complete this one.
For instance, from the
draft: "some contemporary high-end routers are known to inspect up to
192 bytes, while others are known to parse up to 384 bytes of
header.". That's good information since it at least starts to quantify
the router implementation constraints that are mostly the subject of
this draft (this data really needs a reference by the way).
We reference such values for informative purposes. But the goal of this
document is to provide a *qualitative* analysis.
(We did include a reference for the two cited values, but our
responsible AD suggested not to mention specific vendors/products. GIven
your comment, I'll raise the question to him)
If we
establish what the most common limit is, say the 192 bytes that are
mentioned, then we could establish a requirement on routers that sets
a reasonable expectation for hosts stack as to what will be forwarded
with high probability.
As noted, that's certainly out of the scope of this document. That said,
it would seem to me that RFC7872 is providing the kind of information
that you seem to be looking for (modulo a recommendation).
Thanks,
--
Fernando Gont
SI6 Networks
e-mail: fgont@xxxxxxxxxxxxxxx
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
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