Peilin Ye 56af5e749f net/sched: act_skbmod: Add SKBMOD_F_ECN option support ... Currently, when doing rate limiting using the tc-police(8) action, the easiest way is to simply drop the packets which exceed or conform the configured bandwidth limit. Add a new option to tc-skbmod(8), so that users may use the ECN [1] extension to explicitly inform the receiver about the congestion instead of dropping packets "on the floor". The 2 least significant bits of the Traffic Class field in IPv4 and IPv6 headers are used to represent different ECN states [2]: 0b00: "Non ECN-Capable Transport", Non-ECT 0b10: "ECN Capable Transport", ECT(0) 0b01: "ECN Capable Transport", ECT(1) 0b11: "Congestion Encountered", CE As an example: $ tc filter add dev eth0 parent 1: protocol ip prio 10 \ matchall action skbmod ecn Doing the above marks all ECT(0) and ECT(1) packets as CE. It does NOT affect Non-ECT or non-IP packets. In the tc-police scenario mentioned above, users may pipe a tc-police action and a tc-skbmod "ecn" action together to achieve ECN-based rate limiting. For TCP connections, upon receiving a CE packet, the receiver will respond with an ECE packet, asking the sender to reduce their congestion window. However ECN also works with other L4 protocols e.g. DCCP and SCTP [2], and our implementation does not touch or care about L4 headers. The updated tc-skbmod SYNOPSIS looks like the following: tc ... action skbmod { set SETTABLE | swap SWAPPABLE | ecn } ... Only one of "set", "swap" or "ecn" shall be used in a single tc-skbmod command. Trying to use more than one of them at a time is considered undefined behavior; pipe multiple tc-skbmod commands together instead. "set" and "swap" only affect Ethernet packets, while "ecn" only affects IPv{4,6} packets. It is also worth mentioning that, in theory, the same effect could be achieved by piping a "police" action and a "bpf" action using the bpf_skb_ecn_set_ce() helper, but this requires eBPF programming from the user, thus impractical. Depends on patch "net/sched: act_skbmod: Skip non-Ethernet packets". [1] https://datatracker.ietf.org/doc/html/rfc3168 [2] https://en.wikipedia.org/wiki/Explicit_Congestion_Notification Reviewed-by: Cong Wang <cong.wang@bytedance.com> Signed-off-by: Peilin Ye <peilin.ye@bytedance.com> Signed-off-by: David S. Miller <davem@davemloft.net>		2021-07-28 13:19:31 +01:00
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tc_bpf.h
tc_connmark.h
tc_csum.h
tc_ct.h
tc_ctinfo.h
tc_defact.h
tc_gact.h
tc_gate.h	net: qos: introduce a gate control flow action	2020-05-01 16:08:19 -07:00
tc_ife.h
tc_ipt.h
tc_mirred.h
tc_mpls.h	net/sched: act_mpls: Add action to push MPLS LSE before Ethernet header	2020-10-03 17:28:45 -07:00
tc_nat.h
tc_pedit.h
tc_sample.h
tc_skbedit.h
tc_skbmod.h	net/sched: act_skbmod: Add SKBMOD_F_ECN option support	2021-07-28 13:19:31 +01:00
tc_tunnel_key.h
tc_vlan.h	net/sched: act_vlan: Add {POP,PUSH}_ETH actions	2020-10-03 17:28:45 -07:00