Re: [v6ops] new draft: draft-taylor-v6ops-fragdrop

Mark Smith <markzzzsmith@yahoo.com.au> Wed, 31 October 2012 20:03 UTC

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Date: Wed, 31 Oct 2012 13:03:48 -0700
From: Mark Smith <markzzzsmith@yahoo.com.au>
To: Lorenzo Colitti <lorenzo@google.com>, Brian E Carpenter <brian.e.carpenter@gmail.com>
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Cc: "fgont@si6networks.com" <fgont@si6networks.com>, "v6ops@ietf.org" <v6ops@ietf.org>
Subject: Re: [v6ops] new draft: draft-taylor-v6ops-fragdrop
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Hi,

>________________________________
> From: Lorenzo Colitti <lorenzo@google.com>
>To: Brian E Carpenter <brian.e.carpenter@gmail.com> 
>Cc: fgont@si6networks.com; v6ops@ietf.org 
>Sent: Wednesday, 31 October 2012 11:51 PM
>Subject: Re: [v6ops] new draft: draft-taylor-v6ops-fragdrop
> 
>
>On Wed, Oct 31, 2012 at 8:40 PM, Brian E Carpenter <brian.e.carpenter@gmail.com> wrote:
>
>>>> Unfortunately the IPv6 architecture requires the network to
>>>>> be transparent to arbitrary extension header chains.
>>
>>>> Good luck with that in real networks.
>>>
>>> Agreed. "Not gonna happen."
>>
>>I am not totally unrealistic. However, there are some things that
>>the IETF can do to make the reality a bit better than it is at
>>the moment.
>>
>
>
>But why? If you can't get extension headers to work reliably in the Internet (as opposed to in your own network), then what's the point? You still need a fallback plan for when they get dropped, and users don't like waiting. Why not just use the more reliable plan all the time?
>_

So I think, using the "dumb network, smart hosts" model, these measures

(dropping fragments, dropping extension headers, and dropping ICMP) are
making the Internet dumber, and that means the hosts will need to become
smarter. Smarter hosts will either choose to use the simple base capability
of the network (e.g. 1280 MTU), or need to measure the availability of the
features they want to use (PMTUD), without relying on the the network to
indicate which features are and are not currently available (ie. ICMP PTB).

There are already examples of hosts doing this active measuring - packet
loss indicating to TCP that congestion is occurring, measuring PMTU without
relying on ICMP (RFC4821), NAT presence determination using STUN.

Before and unrelated to this thread, I've recently been thinking about

what the impact of the rapid adoption of wireless, mobile multihomed hosts
(a.k.a. smartphones and tables) will be to enterprise and carrier networks,
and what would happen to network QoS and network located security if these
hosts started using Multipath TCP. As these hosts' point of attachment
will never be consistent, and even the performance of the links they're
commonly attached can change over time (i.e. wifi), they'll never be able
to assume a consistent network layer service (throughput, MTU, extension
header support etc., NAT presence, IPv4 and/or IPv6), and therefore will
need to actively measure it if they want to utilise more than just the base
functionality. They'll also need to be responsible for their own security.

The Happy eyeballs technique is another example of a host dynamically
coping with the availability or unreliability of a feature it wants to use.

So perhaps the topic of this draft needs to be encompassed into something

larger, discussing the "dumbing down" of the Internet, and what hosts,
both fixed and rapidly growing numbers of multihomed mobile ones, need to
do to cope when the only reliable indicator from the network layer that
something has gone wrong is packet loss, and that there is no reliable
indicator of what went wrong.


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