lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <50df48f4.0e5b650a.36fa.1452@mx.google.com> Date: Sat, 29 Dec 2012 15:47:55 -0400 From: Jamie Gloudon <jamie.gloudon@...il.com> To: Eric Dumazet <erdnetdev@...il.com> Cc: rick.jones2@...com, netdev@...r.kernel.org Subject: Re: Is keepalive behaving as expected in 3.7.0+/net-next? On Thu, Dec 27, 2012 at 01:54:25PM -0800, Eric Dumazet wrote: > On Fri, 2012-12-21 at 14:05 -0800, Rick Jones wrote: > > I was looking to do a bit more documentation clean-up and thought I > > would work on the descriptions of the "keepalive" sysctls, but first I > > wanted to see if they behaved as the existing descriptions suggested: > > > > > tcp_keepalive_time - INTEGER > > > How often TCP sends out keepalive messages when keepalive is enabled. > > > Default: 2hours. > > > > > > tcp_keepalive_probes - INTEGER > > > How many keepalive probes TCP sends out, until it decides that the > > > connection is broken. Default value: 9. > > > > > > tcp_keepalive_intvl - INTEGER > > > How frequently the probes are send out. Multiplied by > > > tcp_keepalive_probes it is time to kill not responding connection, > > > after probes started. Default value: 75sec i.e. connection > > > will be aborted after ~11 minutes of retries. > > > > I interpreted all that that as: When a connection is idle, TCP will > > send a keepalive probe every tcp_keepalive_time seconds. If a response > > to a keepalive probe is not received, TCP will resend (retransmit) it > > every tcp_keepalive_intvl seconds. > > > > However, what I see is that on a connection where the remote is indeed > > still there, only the first keepalive probe is sent after > > tcp_keepalive_time, and thereafter it is sent every tcp_keepalive_intvl > > seconds. > > > > Now, some of this may relate to my being impatient - rather than wait > > two hours for the first probe, I set tcp_keepalive_time to 3 seconds, > > and tcp_keepalive_intvl to 7 seconds. I then kicked-off a ./configure > > --intervals-enable netperf TCP_RR test with a burst of one and a wait > > time of 90 seconds and got the following (trimmed) trace: > > > > 13:43:46.879133 IP netnextraj.43054 > netnextraj2.srvr: Flags [S], seq > > 807869796, win 14600, options [mss 1460,sackOK,TS val 133470 ecr > > 0,nop,wscale 7], length 0 > > 13:43:46.880091 IP netnextraj2.srvr > netnextraj.43054: Flags [S.], seq > > 1522345902, ack 807869797, win 14480, options [mss 1460,sackOK,TS val > > 136186 ecr 133470,nop,wscale 4], length 0 > > 13:43:46.880114 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack > > 1, win 115, options [nop,nop,TS val 133470 ecr 136186], length 0 > > 13:43:46.880306 IP netnextraj.43054 > netnextraj2.srvr: Flags [P.], seq > > 1:11, ack 1, win 115, options [nop,nop,TS val 133470 ecr 136186], length 10 > > 13:43:46.880948 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack > > 11, win 905, options [nop,nop,TS val 136187 ecr 133470], length 0 > > 13:43:46.880964 IP netnextraj2.srvr > netnextraj.43054: Flags [P.], seq > > 1:11, ack 11, win 905, options [nop,nop,TS val 136187 ecr 133470], length 10 > > 13:43:46.881161 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack > > 11, win 115, options [nop,nop,TS val 133470 ecr 136187], length 0 > > > > The first probe above comes after 3 seconds - tcp_keepalive_time - at > > 13:43:49 > > > > 13:43:49.886752 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack > > 11, win 115, options [nop,nop,TS val 134222 ecr 136187], length 0 > > > > And it does seem to elicit a response: > > > > 13:43:49.887530 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack > > 11, win 905, options [nop,nop,TS val 136938 ecr 133470], length 0 > > > > > > Now it starts sending probes every 7 seconds (tcp_keepalive_intvl): > > > > 13:43:56.903576 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack > > 11, win 115, options [nop,nop,TS val 135976 ecr 136938], length 0 > > 13:43:56.904480 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack > > 11, win 905, options [nop,nop,TS val 138693 ecr 133470], length 0 > > 13:44:03.910744 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack > > 11, win 115, options [nop,nop,TS val 137728 ecr 138693], length 0 > > 13:44:03.911623 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack > > 11, win 905, options [nop,nop,TS val 140444 ecr 133470], length 0 > > > > I;ve deleted the next 9 or so probes... It continues, and doesn't > > terminate the connection, so I assume it was happy with the responses to > > the probes. > > > > 13:45:13.990746 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack > > 11, win 115, options [nop,nop,TS val 155248 ecr 156213], length 0 > > 13:45:13.991578 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack > > 11, win 905, options [nop,nop,TS val 157965 ecr 133470], length 0 > > > > Now the next netperf transaction happens: > > > > 13:45:16.879222 IP netnextraj.43054 > netnextraj2.srvr: Flags [P.], seq > > 11:21, ack 11, win 115, options [nop,nop,TS val 155970 ecr 157965], > > length 10 > > 13:45:16.880033 IP netnextraj2.srvr > netnextraj.43054: Flags [P.], seq > > 11:21, ack 21, win 905, options [nop,nop,TS val 158687 ecr 155970], > > length 10 > > 13:45:16.880220 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack > > 21, win 115, options [nop,nop,TS val 155970 ecr 158687], length 0 > > > > But the next keepalive probe is tcp_keepalive_intvl seconds after the > > last one, rather than that many, or tcp_keepalive_time seconds after the > > connection was last "active." > > > > 13:45:20.998739 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack > > 21, win 115, options [nop,nop,TS val 157000 ecr 158687], length 0 > > 13:45:20.999754 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack > > 21, win 905, options [nop,nop,TS val 159717 ecr 155970], length 0 > > 13:45:28.006747 IP netnextraj.43054 > netnextraj2.srvr: Flags [.], ack > > 21, win 115, options [nop,nop,TS val 158752 ecr 159717], length 0 > > 13:45:28.007624 IP netnextraj2.srvr > netnextraj.43054: Flags [.], ack > > 21, win 905, options [nop,nop,TS val 161469 ecr 155970], length 0 > > > > Is this the expected behaviour? If I reverse the values - make > > tcp_keepalive_time 7 and tcp_keepalive_intvl 3, it seems that all the > > probes are after 7 seconds. > > > > rick jones > > Not sure if it makes sense to have > tcp_keepalive_intvl > tcp_keepalive_time > > time should be an order of magnitude bigger than intvl. > > keepalive timer is not reset each time we receive a valid frame, it > would be very expensive. > > Its a long period timer. > > First interval is tcp_keepalive_time, and subsequent interval are > tcp_keepalive_intvl > > Each time timer is fired (once every 7200 seconds), we re-arm it with > the observed elapsed time (keepalive_time_elapsed) > > Fixing this would require to add a timestamp in inet socket, to remember > time of next/last probe, and firing the timer using > min(keepalive_time_when(tp), keepalive_intvl_when(tp)) > > Probably not worth it. > > Make a lot of sense. However, I got the impression from Rick that having tcp_keepalive_intvl > tcp_keepalive_time behaved correctly in older versions of the kernel. Regards, Jamie Gloudon -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists