<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi, All<div class=""><br class=""></div><div class="">Recently, one of my tinc client always suffer connection drop, I was suspect the connection was not stable to cause this issue, and BTW, I’ve set the PingTimeout to 10 seconds already, but this situation still happens a lot sometimes, but when the connection drop happens, the connection recovery pretty fast, normally in a minutes.</div><div class=""><br class=""></div><div class="">In order to deep dive into the cause, or proven the network quality problem, I capture the tcpdump from client to server to see what’s going on.</div><div class=""><br class=""></div><div class="">Client side configure:</div><div class=""><br class=""></div><div class="">tinc.conf:</div><div class="">AddressFamily = ipv4<br class="">Name = box2<br class="">ProcessPriority = high<br class="">PingTimeout = 10<br class="">TunnelServer = yes<br class="">ConnectTo = abc</div><div class=""><br class=""></div><div class="">box2:</div><div class="">Subnet = 10.0.0.102/32<br class="">IndirectData = yes<br class="">Port = 8102<br class=""><br class=""></div><div class=""><br class=""></div><div class="">Server side configure:</div><div class=""><br class=""></div><div class="">tinc.conf:</div><div class="">Name = abc<br class="">AddressFamily = ipv4<br class="">PingTimeout = 10</div><div class=""><br class=""></div><div class="">abc:</div><div class="">Address = 47.152.x.x(public address, 172.31.x.x as the private real NIC address)<br class="">Subnet = 10.0.0.16/32<br class="">Port = 443<br class="">IndirectData = yes</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">As you saw from <a href="https://ibb.co/mRyG3a" class="">https://ibb.co/mRyG3a</a>, the connection get drop and re-establish very frequently, and the one highlighted as yellow, it’s the connection we’ll go into deep dive, which happens on 07:41:35, when you cross check this with <a href="https://ibb.co/b740UF" class="">https://ibb.co/b740UF</a>, you’ll find that event match the packet of 485/486 which is the server side RST packet to close the connection, but let’s move our focus to the packet of 481, which is the packet server(47.52.x.x) send to tinc client to close the connection, which happens at 07:41:27.</div><div class=""><br class=""></div><div class="">Then the below logs are captured from tinc server side that you can see at 07:41:27, the server report it didn’t receive any Ping respond from the client, so that it close the connection, but let’s take a look for the tcpdump from server side, which is the server_tcpdump(in attachment). No.463 packet is the one where server send FIN to tinc client to close the connection at 07:41:27, but the assumption is server didn’t receive any Ping response from client so that the server initiate the closure, but as we see from the screenshot that, the server(172.31.x.x) received and sent couple of packets with tinc client(123.151.x.x) before 07:41:27, which is <a href="https://ibb.co/isECbv" class="">https://ibb.co/isECbv</a>, for example packet of 457~462. So why tinc server believe it doesn’t receive any response from tinc client, but the packet capture shows it had regular communication with tinc client with 10 second. I would like to get to know the cause for this tinc frequent drop issue.</div><div class=""><br class=""></div><div class="">Sep 5 07:41:27 abc tinc.myvpn[8510]: box2 (123.151.x.x port 51402) didn't respond to PING in 10 seconds<br class="">Sep 5 07:41:27 abc tinc.myvpn[8510]: Closing connection with box2 (123.151.x.x port 51402)<br class="">Sep 5 07:41:40 abc tinc.myvpn[8510]: Connection with box2 (123.151.x.x port 51418) activated<br class=""><br class=""></div><div class=""><br class=""></div><div class=""><div style="font-size: 12px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Best Regards</div><div class=""><br class=""></div><div class="">Bright</div></div><span style="font-family: 'Helvetica Neue', Helvetica, STheiti, 微软雅黑, 黑体, Arial, Tahoma, sans-serif, serif; font-size: x-large; line-height: 36px; background-color: rgb(255, 255, 255);" class="">✉</span></div></div></body></html>