Re: [Int-area] Comments on draft-ietf-intarea-frag-fragile-06

Stewart Bryant <> Wed, 30 January 2019 14:17 UTC

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To: Tom Herbert <>, Fred Baker <>
Cc: int-area <>
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From: Stewart Bryant <>
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Date: Wed, 30 Jan 2019 14:17:42 +0000
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Subject: Re: [Int-area] Comments on draft-ietf-intarea-frag-fragile-06
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> That's true for IPv4,the only way to do stateless ECMP and have
> fragments follow the same path as non-fragments is to hash over the IP
> addresses only.

There is not enough entropy in that.

I remember the original ECMP studies, and if the designers could have 
got away with just SA/DA/Prot they would have. In those days we were 
using s/w forwarders and the ECMP "feature" cost headline PPS which in 
those days was the key metric.

> For IPv6 we can do better. The flow label allows finer
> grained per-flow routing, but still only requires inspection of IP
> header so keeping fragments in order just works.

If you can trust it.

- Stewart