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Re: [v6ops] IPv6 fragmentation experience

Joe Touch <touch@strayalpha.com> Fri, 23 March 2018 00:26 UTC

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To: Jen Linkova <furry13@gmail.com>, Gert Doering <gert@space.net>
Cc: "v6ops@ietf.org WG" <v6ops@ietf.org>
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From: Joe Touch <touch@strayalpha.com>
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Date: Thu, 22 Mar 2018 17:26:06 -0700
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Subject: Re: [v6ops] IPv6 fragmentation experience
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On 3/22/2018 9:45 AM, Jen Linkova wrote:
> Actually,,, There is one really nasty scenario when hashing is causing
> not just reordering but packet loss.
> Scenario 1.1: a router R1 is doing ECMP, sends 1st fragment to R2
> while other fragments went to R3. If the paths to the destination
> (anycast!) on R2 and R3 do not converge, 
(to finish that sentence correctly) then your routing is broken anyway
and all bets are off. Don't blame either fragmentation or ECMP for that
problem.

...
> Scenario 1.2: a load-balancer using 5-tupes and a number of end
> systems behind it. If the first fragment is forwarded by using L4
> info,
(again, to finish the sentence correctly) then the load balancer should
either reassemble the fragments or keep enough state to make sure they
fate-share to the same recipient. Otherwise, what you call a "load
balancer" is basically doing random forwarding, which is broken routing,
and again -- all bets are off.

Fragmentation isn't the cause of these problems; broken routing is.

Joe

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