path: root/Documentation
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authorTom Herbert <tom@herbertland.com>2015-04-29 15:33:21 -0700
committerDavid S. Miller <davem@davemloft.net>2015-05-03 21:58:01 -0400
commit82a584b7cd366511a22e37675b029cf2fb58e291 (patch)
treeef5907021414a1ab539ca398ab7c43810dacfc75 /Documentation
parent7035870d1219f5cd86128edcb4c3517def632ad3 (diff)
ipv6: Flow label state ranges
This patch divides the IPv6 flow label space into two ranges: 0-7ffff is reserved for flow label manager, 80000-fffff will be used for creating auto flow labels (per RFC6438). This only affects how labels are set on transmit, it does not affect receive. This range split can be disbaled by systcl. Background: IPv6 flow labels have been an unmitigated disappointment thus far in the lifetime of IPv6. Support in HW devices to use them for ECMP is lacking, and OSes don't turn them on by default. If we had these we could get much better hashing in IPv6 networks without resorting to DPI, possibly eliminating some of the motivations to to define new encaps in UDP just for getting ECMP. Unfortunately, the initial specfications of IPv6 did not clarify how they are to be used. There has always been a vague concept that these can be used for ECMP, flow hashing, etc. and we do now have a good standard how to this in RFC6438. The problem is that flow labels can be either stateful or stateless (as in RFC6438), and we are presented with the possibility that a stateless label may collide with a stateful one. Attempts to split the flow label space were rejected in IETF. When we added support in Linux for RFC6438, we could not turn on flow labels by default due to this conflict. This patch splits the flow label space and should give us a path to enabling auto flow labels by default for all IPv6 packets. This is an API change so we need to consider compatibility with existing deployment. The stateful range is chosen to be the lower values in hopes that most uses would have chosen small numbers. Once we resolve the stateless/stateful issue, we can proceed to look at enabling RFC6438 flow labels by default (starting with scaled testing). Signed-off-by: Tom Herbert <tom@herbertland.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation')
1 files changed, 8 insertions, 0 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 071fb18dc57c..5095c63e50ed 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1213,6 +1213,14 @@ auto_flowlabels - BOOLEAN
FALSE: disabled
Default: false
+flowlabel_state_ranges - BOOLEAN
+ Split the flow label number space into two ranges. 0-0x7FFFF is
+ reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF
+ is reserved for stateless flow labels as described in RFC6437.
+ TRUE: enabled
+ FALSE: disabled
+ Default: true
anycast_src_echo_reply - BOOLEAN
Controls the use of anycast addresses as source addresses for ICMPv6
echo reply

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