linux/include
Florian Westphal f7b3bec6f5 net: allow setting ecn via routing table
This patch allows to set ECN on a per-route basis in case the sysctl
tcp_ecn is not set to 1. In other words, when ECN is set for specific
routes, it provides a tcp_ecn=1 behaviour for that route while the rest
of the stack acts according to the global settings.

One can use 'ip route change dev $dev $net features ecn' to toggle this.

Having a more fine-grained per-route setting can be beneficial for various
reasons, for example, 1) within data centers, or 2) local ISPs may deploy
ECN support for their own video/streaming services [1], etc.

There was a recent measurement study/paper [2] which scanned the Alexa's
publicly available top million websites list from a vantage point in US,
Europe and Asia:

Half of the Alexa list will now happily use ECN (tcp_ecn=2, most likely
blamed to commit 255cac91c3 ("tcp: extend ECN sysctl to allow server-side
only ECN") ;)); the break in connectivity on-path was found is about
1 in 10,000 cases. Timeouts rather than receiving back RSTs were much
more common in the negotiation phase (and mostly seen in the Alexa
middle band, ranks around 50k-150k): from 12-thousand hosts on which
there _may_ be ECN-linked connection failures, only 79 failed with RST
when _not_ failing with RST when ECN is not requested.

It's unclear though, how much equipment in the wild actually marks CE
when buffers start to fill up.

We thought about a fallback to non-ECN for retransmitted SYNs as another
global option (which could perhaps one day be made default), but as Eric
points out, there's much more work needed to detect broken middleboxes.

Two examples Eric mentioned are buggy firewalls that accept only a single
SYN per flow, and middleboxes that successfully let an ECN flow establish,
but later mark CE for all packets (so cwnd converges to 1).

 [1] http://www.ietf.org/proceedings/89/slides/slides-89-tsvarea-1.pdf, p.15
 [2] http://ecn.ethz.ch/

Joint work with Daniel Borkmann.

Reference: http://thread.gmane.org/gmane.linux.network/335797
Suggested-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-11-04 16:06:09 -05:00
..
acpi ACPI and power management updates for 3.18-rc2 2014-10-24 11:29:31 -07:00
asm-generic Merge git://git.infradead.org/users/eparis/audit 2014-10-19 16:25:56 -07:00
clocksource
crypto crypto: LLVMLinux: Add macro to remove use of VLAIS in crypto code 2014-10-14 10:51:22 +02:00
drm drm/mst: rework payload table allocation to conform better. 2014-10-13 14:40:53 +10:00
dt-bindings ARM: i.MX6: Fix "emi" clock name typo 2014-10-25 20:01:09 +08:00
keys KEYS: Restore partial ID matching functionality for asymmetric keys 2014-10-06 15:21:05 +01:00
kvm arm/arm64: KVM: Fix BE accesses to GICv2 EISR and ELRSR regs 2014-10-16 10:57:41 +02:00
linux net: add rbnode to struct sk_buff 2014-11-03 16:13:03 -05:00
math-emu
media Merge branch 'patchwork' into v4l_for_linus 2014-10-09 14:00:54 -03:00
memory
misc cxl: Add new header for call backs and structs 2014-10-08 20:15:43 +11:00
net net: allow setting ecn via routing table 2014-11-04 16:06:09 -05:00
pcmcia
ras PCI/AER: Rename PCI_ERR_UNC_TRAIN to PCI_ERR_UNC_UND 2014-09-25 09:42:40 -06:00
rdma IB/mlx5, iser, isert: Add Signature API additions 2014-10-09 00:10:53 -07:00
rxrpc
scsi Merge branch 'for-linus' of git://git.open-osd.org/linux-open-osd 2014-10-21 12:53:45 -07:00
soc/tegra
sound Merge branch 'for-linus' of git://git.infradead.org/users/vkoul/slave-dma 2014-10-18 18:11:04 -07:00
target target: Add force_pr_aptpl device attribute 2014-10-04 05:41:20 +00:00
trace Merge branch 'urgent-for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/urgent 2014-10-30 07:37:37 +01:00
uapi Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2014-11-01 14:53:27 -04:00
video fbdev changes for 3.18 2014-10-18 18:03:02 -07:00
xen xen: remove DEFINE_XENBUS_DRIVER() macro 2014-10-06 10:27:57 +01:00
Kbuild