netdev - RE: [PATCH v4 net-next 0/2] ipv4: Hash-based multipath routing

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Date:	Tue, 29 Sep 2015 12:38:48 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Peter Nørlund' <pch@...bogen.com>,
	David Miller <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kuznet@....inr.ac.ru" <kuznet@....inr.ac.ru>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"yoshfuji@...ux-ipv6.org" <yoshfuji@...ux-ipv6.org>,
	"kaber@...sh.net" <kaber@...sh.net>
Subject: RE: [PATCH v4 net-next 0/2] ipv4: Hash-based multipath routing

From: Peter Nørlund
> Sent: 29 September 2015 12:29
...
> As for using L4 hashing with anycast, CloudFlare apparently does L4
> hashing - they could have disabled it, but they didn't. Besides,
> analysis of my own load balancers showed that only one in every
> 500,000,000 packets is fragmented. And even if I hit a fragmented
> packet, it is only a problem if the packet hits the wrong load
> balancer, and if that load balancer haven't been updated with the state
> from another load balancer (that is, one of the very first packets). It
> is still a possible scenario though - especially with large HTTP
> cookies or file uploads. But apparently it is a common problem that IP
> fragments gets dropped on the Internet, so I suspect that ECMP+Anycast
> sites are just part of the pool of problematic sites for people with
> fragments.

Fragmentation is usually more of an issue with UDP than TCP.
Some SIP messages can get fragmented...

	David