什麼可能導致 twitterbot 需要 6 秒來下載小圖像資源？

很多（大多數）時間 twitter 對某些圖像發出 http 請求，響應時間（由 nginx 在日誌中記錄）需要 6 秒。然而，其他網站（例如 facebook），有時還有 twitter，通常會在 0.2 秒或更短的時間內獲得響應。

並不是響應時間“只是慢”，而是響應時間幾乎總是接近 6 秒。就像那將是模態響應時間。

Twitter 說這可能是一個路由問題，我應該嘗試在另一個域上託管圖像（大概它們意味著在另一個 IP 上），但我不相信。

有一些關於時間的事情讓我覺得還有其他事情發生。

我檢查了 robots.txt（這不會影響響應時間）；我沒有在 nginx 中實現任何速率限制；也不是 twitterbot 真的在打擊網站，請求之間通常有幾分鐘的時間！

我注意到的唯一奇怪的事情是，twitter 有時會同時對同一資源發出兩個請求。例如

{"rsTime":"2022-01-05T23:07:49+00:00","rsStatus":"200","rqIp":"x.x.x.x","rq":"GET /sites/default/files/share-images/node-3211-202112151443.jpg HTTP/1.1","rqUser":"","rqRef":"","rqUA":"Twitterbot/1.0","rsB":"196275","rsTook":"6.604","phpTook":""}

{"rsTime":"2022-01-05T23:07:49+00:00","rsStatus":"200","rqIp":"x.x.x.x","rq":"GET /sites/default/files/share-images/node-3211-202112151443.jpg HTTP/1.1","rqUser":"","rqRef":"","rqUA":"Twitterbot/1.0","rsB":"196275","rsTook":"6.605","phpTook":""}

如果有幫助，這裡是請求的標頭：

HTTP/1.1 200 OK
Accept-Ranges: bytes
Cache-Control: max-age=2592000
Connection: keep-alive
Content-Length: 343376
Content-Type: image/jpeg
Date: Thu, 06 Jan 2022 17:45:21 GMT
ETag: "619d2951-53d50"
Expires: Sat, 05 Feb 2022 17:45:21 GMT
Keep-Alive: timeout=10
Last-Modified: Tue, 23 Nov 2021 17:48:01 GMT
Server: nginx

我相信這是 nginx 配置的相關部分：

sendfile on;             
tcp_nopush on;           
tcp_nodelay on;          
types_hash_max_size 2048;
server_tokens off;
client_body_timeout 60;                                
client_header_timeout 60;                   
keepalive_timeout 10 10;                               
send_timeout 60;                                       
reset_timedout_connection on;                          
expires 30d;
open_file_cache max=3000 inactive=120s;                           
open_file_cache_valid 45s;
open_file_cache_min_uses 2;
open_file_cache_errors off;

編輯：tcpdump 數據，如評論中所建議

當我在 twitter 上發布連結時，我使用 tcpdump 在 mysite 和 twitter 的站點之間轉儲 https 數據。Twitter 發出了 2 個 http 請求：一個用於頁面（0.18 秒），一個用於圖像（6.67 秒）。

我對 tcpdump 完全陌生，所以不確定我在尋找什麼。

07.301756 IP theirsite.36652 > mysite.https: Flags [SEW], seq 350223635, win 65535, options [mss 1460,sackOK,TS val 3744650926 ecr 0,nop,wscale 8], length 0
07.301814 IP mysite.https > theirsite.36652: Flags [S.E], seq 3699217149, ack 350223636, win 65160, options [mss 1460,sackOK,TS val 3624184444 ecr 3744650926,nop,wscale 7], length 0
07.400999 IP theirsite.36652 > mysite.https: Flags [.], ack 1, win 256, options [nop,nop,TS val 3744651026 ecr 3624184444], length 0
07.401067 IP theirsite.36652 > mysite.https: Flags [P.], seq 1:153, ack 1, win 256, options [nop,nop,TS val 3744651026 ecr 3624184444], length 152
07.401084 IP mysite.https > theirsite.36652: Flags [.E], ack 153, win 508, options [nop,nop,TS val 3624184543 ecr 3744651026], length 0
07.401638 IP mysite.https > theirsite.36652: Flags [.E], seq 1:2897, ack 153, win 508, options [nop,nop,TS val 3624184543 ecr 3744651026], length 2896
07.401676 IP mysite.https > theirsite.36652: Flags [P.E], seq 2897:4097, ack 153, win 508, options [nop,nop,TS val 3624184543 ecr 3744651026], length 1200
07.403373 IP mysite.https > theirsite.36652: Flags [P.E], seq 4097:4433, ack 153, win 508, options [nop,nop,TS val 3624184545 ecr 3744651026], length 336
07.500676 IP theirsite.36652 > mysite.https: Flags [.E], ack 4097, win 288, options [nop,nop,TS val 3744651125 ecr 3624184543], length 0
07.502402 IP theirsite.36652 > mysite.https: Flags [.E], ack 4433, win 300, options [nop,nop,TS val 3744651127 ecr 3624184545], length 0
07.503493 IP theirsite.36652 > mysite.https: Flags [P.EW], seq 153:246, ack 4433, win 300, options [nop,nop,TS val 3744651128 ecr 3624184545], length 93
07.503519 IP mysite.https > theirsite.36652: Flags [.E], ack 246, win 508, options [nop,nop,TS val 3624184645 ecr 3744651128], length 0
07.503926 IP mysite.https > theirsite.36652: Flags [P.EW], seq 4433:4691, ack 246, win 508, options [nop,nop,TS val 3624184646 ecr 3744651128], length 258
07.603028 IP theirsite.36652 > mysite.https: Flags [.E], ack 4691, win 311, options [nop,nop,TS val 3744651228 ecr 3624184646], length 0
07.603159 IP theirsite.36652 > mysite.https: Flags [P.EW], seq 246:595, ack 4691, win 311, options [nop,nop,TS val 3744651228 ecr 3624184646], length 349
07.603188 IP mysite.https > theirsite.36652: Flags [.E], ack 595, win 506, options [nop,nop,TS val 3624184745 ecr 3744651228], length 0
07.792960 IP mysite.https > theirsite.36652: Flags [.EW], seq 4691:6139, ack 595, win 506, options [nop,nop,TS val 3624184935 ecr 3744651228], length 1448
07.892024 IP theirsite.36652 > mysite.https: Flags [.E], ack 6139, win 322, options [nop,nop,TS val 3744651517 ecr 3624184935], length 0
07.892047 IP mysite.https > theirsite.36652: Flags [.EW], seq 6139:7587, ack 595, win 506, options [nop,nop,TS val 3624185034 ecr 3744651517], length 1448
07.990993 IP theirsite.36652 > mysite.https: Flags [.E], ack 7587, win 334, options [nop,nop,TS val 3744651616 ecr 3624185034], length 0
07.991014 IP mysite.https > theirsite.36652: Flags [.EW], seq 7587:9035, ack 595, win 506, options [nop,nop,TS val 3624185133 ecr 3744651616], length 1448
08.090023 IP theirsite.36652 > mysite.https: Flags [.E], ack 9035, win 345, options [nop,nop,TS val 3744651715 ecr 3624185133], length 0
08.090053 IP mysite.https > theirsite.36652: Flags [.EW], seq 9035:10483, ack 595, win 506, options [nop,nop,TS val 3624185232 ecr 3744651715], length 1448
08.189127 IP theirsite.36652 > mysite.https: Flags [.E], ack 10483, win 356, options [nop,nop,TS val 3744651814 ecr 3624185232], length 0
08.189150 IP mysite.https > theirsite.36652: Flags [.EW], seq 10483:11931, ack 595, win 506, options [nop,nop,TS val 3624185331 ecr 3744651814], length 1448
08.288177 IP theirsite.36652 > mysite.https: Flags [.E], ack 11931, win 368, options [nop,nop,TS val 3744651913 ecr 3624185331], length 0
08.288219 IP mysite.https > theirsite.36652: Flags [.EW], seq 11931:13379, ack 595, win 506, options [nop,nop,TS val 3624185430 ecr 3744651913], length 1448
08.387287 IP theirsite.36652 > mysite.https: Flags [.E], ack 13379, win 379, options [nop,nop,TS val 3744652012 ecr 3624185430], length 0
08.387316 IP mysite.https > theirsite.36652: Flags [.EW], seq 13379:14827, ack 595, win 506, options [nop,nop,TS val 3624185529 ecr 3744652012], length 1448
08.486350 IP theirsite.36652 > mysite.https: Flags [.E], ack 14827, win 390, options [nop,nop,TS val 3744652111 ecr 3624185529], length 0
08.486372 IP mysite.https > theirsite.36652: Flags [P.EW], seq 14827:16256, ack 595, win 506, options [nop,nop,TS val 3624185628 ecr 3744652111], length 1429
08.585430 IP theirsite.36652 > mysite.https: Flags [.E], ack 16256, win 402, options [nop,nop,TS val 3744652210 ecr 3624185628], length 0
11.555117 IP theirsite.37999 > mysite.https: Flags [SEW], seq 1059140554, win 65535, options [mss 1460,sackOK,TS val 2940663245 ecr 0,nop,wscale 8], length 0
11.555147 IP mysite.https > theirsite.37999: Flags [S.E], seq 4137859394, ack 1059140555, win 65160, options [mss 1460,sackOK,TS val 3624188697 ecr 2940663245,nop,wscale 7], length 0
11.654266 IP theirsite.37999 > mysite.https: Flags [.], ack 1, win 256, options [nop,nop,TS val 2940663345 ecr 3624188697], length 0
11.654320 IP theirsite.37999 > mysite.https: Flags [P.], seq 1:153, ack 1, win 256, options [nop,nop,TS val 2940663345 ecr 3624188697], length 152
11.654336 IP mysite.https > theirsite.37999: Flags [.E], ack 153, win 508, options [nop,nop,TS val 3624188796 ecr 2940663345], length 0
11.654658 IP mysite.https > theirsite.37999: Flags [.E], seq 1:2897, ack 153, win 508, options [nop,nop,TS val 3624188796 ecr 2940663345], length 2896
11.654676 IP mysite.https > theirsite.37999: Flags [P.E], seq 2897:4097, ack 153, win 508, options [nop,nop,TS val 3624188796 ecr 2940663345], length 1200
11.656243 IP mysite.https > theirsite.37999: Flags [P.E], seq 4097:4433, ack 153, win 508, options [nop,nop,TS val 3624188798 ecr 2940663345], length 336
11.753727 IP theirsite.37999 > mysite.https: Flags [.E], ack 4097, win 288, options [nop,nop,TS val 2940663444 ecr 3624188796], length 0
11.755266 IP theirsite.37999 > mysite.https: Flags [.E], ack 4433, win 300, options [nop,nop,TS val 2940663446 ecr 3624188798], length 0
11.756355 IP theirsite.37999 > mysite.https: Flags [P.EW], seq 153:246, ack 4433, win 300, options [nop,nop,TS val 2940663447 ecr 3624188798], length 93
11.756399 IP mysite.https > theirsite.37999: Flags [.E], ack 246, win 508, options [nop,nop,TS val 3624188898 ecr 2940663447], length 0
11.756842 IP mysite.https > theirsite.37999: Flags [P.EW], seq 4433:4691, ack 246, win 508, options [nop,nop,TS val 3624188899 ecr 2940663447], length 258
11.855874 IP theirsite.37999 > mysite.https: Flags [.E], ack 4691, win 311, options [nop,nop,TS val 2940663546 ecr 3624188899], length 0
11.856034 IP theirsite.37999 > mysite.https: Flags [P.EW], seq 246:627, ack 4691, win 311, options [nop,nop,TS val 2940663546 ecr 3624188899], length 381
11.856057 IP mysite.https > theirsite.37999: Flags [.E], ack 627, win 506, options [nop,nop,TS val 3624188998 ecr 2940663546], length 0
11.856303 IP mysite.https > theirsite.37999: Flags [.EW], seq 4691:6139, ack 627, win 506, options [nop,nop,TS val 3624188998 ecr 2940663546], length 1448
11.955431 IP theirsite.37999 > mysite.https: Flags [.E], ack 6139, win 322, options [nop,nop,TS val 2940663646 ecr 3624188998], length 0
11.955505 IP mysite.https > theirsite.37999: Flags [.EW], seq 6139:7587, ack 627, win 506, options [nop,nop,TS val 3624189097 ecr 2940663646], length 1448
12.054716 IP theirsite.37999 > mysite.https: Flags [.E], ack 7587, win 334, options [nop,nop,TS val 2940663745 ecr 3624189097], length 0
12.054805 IP mysite.https > theirsite.37999: Flags [.EW], seq 7587:9035, ack 627, win 506, options [nop,nop,TS val 3624189197 ecr 2940663745], length 1448
12.153874 IP theirsite.37999 > mysite.https: Flags [.E], ack 9035, win 345, options [nop,nop,TS val 2940663844 ecr 3624189197], length 0
12.153924 IP mysite.https > theirsite.37999: Flags [.EW], seq 9035:10483, ack 627, win 506, options [nop,nop,TS val 3624189296 ecr 2940663844], length 1448
12.253082 IP theirsite.37999 > mysite.https: Flags [.E], ack 10483, win 356, options [nop,nop,TS val 2940663943 ecr 3624189296], length 0
12.253134 IP mysite.https > theirsite.37999: Flags [.EW], seq 10483:11931, ack 627, win 506, options [nop,nop,TS val 3624189395 ecr 2940663943], length 1448
12.352340 IP theirsite.37999 > mysite.https: Flags [.E], ack 11931, win 368, options [nop,nop,TS val 2940664043 ecr 3624189395], length 0
12.352409 IP mysite.https > theirsite.37999: Flags [.EW], seq 11931:13379, ack 627, win 506, options [nop,nop,TS val 3624189494 ecr 2940664043], length 1448
12.451567 IP theirsite.37999 > mysite.https: Flags [.E], ack 13379, win 379, options [nop,nop,TS val 2940664142 ecr 3624189494], length 0
12.451615 IP mysite.https > theirsite.37999: Flags [.EW], seq 13379:14827, ack 627, win 506, options [nop,nop,TS val 3624189593 ecr 2940664142], length 1448
12.550697 IP theirsite.37999 > mysite.https: Flags [.E], ack 14827, win 390, options [nop,nop,TS val 2940664241 ecr 3624189593], length 0
12.550736 IP mysite.https > theirsite.37999: Flags [.EW], seq 14827:16275, ack 627, win 506, options [nop,nop,TS val 3624189693 ecr 2940664241], length 1448
12.649774 IP theirsite.37999 > mysite.https: Flags [.E], ack 16275, win 402, options [nop,nop,TS val 2940664340 ecr 3624189693], length 0
12.649810 IP mysite.https > theirsite.37999: Flags [.EW], seq 16275:17723, ack 627, win 506, options [nop,nop,TS val 3624189792 ecr 2940664340], length 1448
12.748972 IP theirsite.37999 > mysite.https: Flags [.E], ack 17723, win 413, options [nop,nop,TS val 2940664439 ecr 3624189792], length 0
12.749025 IP mysite.https > theirsite.37999: Flags [.EW], seq 17723:19171, ack 627, win 506, options [nop,nop,TS val 3624189891 ecr 2940664439], length 1448
12.848133 IP theirsite.37999 > mysite.https: Flags [.E], ack 19171, win 424, options [nop,nop,TS val 2940664538 ecr 3624189891], length 0
12.848171 IP mysite.https > theirsite.37999: Flags [.EW], seq 19171:20619, ack 627, win 506, options [nop,nop,TS val 3624189990 ecr 2940664538], length 1448
12.947232 IP theirsite.37999 > mysite.https: Flags [.E], ack 20619, win 436, options [nop,nop,TS val 2940664637 ecr 3624189990], length 0
12.947273 IP mysite.https > theirsite.37999: Flags [.EW], seq 20619:22067, ack 627, win 506, options [nop,nop,TS val 3624190089 ecr 2940664637], length 1448
13.046357 IP theirsite.37999 > mysite.https: Flags [.E], ack 22067, win 447, options [nop,nop,TS val 2940664737 ecr 3624190089], length 0
13.046386 IP mysite.https > theirsite.37999: Flags [.EW], seq 22067:23515, ack 627, win 506, options [nop,nop,TS val 3624190188 ecr 2940664737], length 1448
13.145398 IP theirsite.37999 > mysite.https: Flags [.E], ack 23515, win 458, options [nop,nop,TS val 2940664836 ecr 3624190188], length 0
13.145426 IP mysite.https > theirsite.37999: Flags [.EW], seq 23515:24963, ack 627, win 506, options [nop,nop,TS val 3624190287 ecr 2940664836], length 1448
13.244504 IP theirsite.37999 > mysite.https: Flags [.E], ack 24963, win 469, options [nop,nop,TS val 2940664935 ecr 3624190287], length 0
13.244532 IP mysite.https > theirsite.37999: Flags [.EW], seq 24963:26411, ack 627, win 506, options [nop,nop,TS val 3624190386 ecr 2940664935], length 1448
13.343650 IP theirsite.37999 > mysite.https: Flags [.E], ack 26411, win 481, options [nop,nop,TS val 2940665034 ecr 3624190386], length 0
13.343716 IP mysite.https > theirsite.37999: Flags [.EW], seq 26411:27859, ack 627, win 506, options [nop,nop,TS val 3624190486 ecr 2940665034], length 1448
13.442769 IP theirsite.37999 > mysite.https: Flags [.E], ack 27859, win 492, options [nop,nop,TS val 2940665133 ecr 3624190486], length 0
13.442795 IP mysite.https > theirsite.37999: Flags [.EW], seq 27859:29307, ack 627, win 506, options [nop,nop,TS val 3624190585 ecr 2940665133], length 1448
13.541819 IP theirsite.37999 > mysite.https: Flags [.E], ack 29307, win 503, options [nop,nop,TS val 2940665232 ecr 3624190585], length 0
13.541880 IP mysite.https > theirsite.37999: Flags [.EW], seq 29307:30755, ack 627, win 506, options [nop,nop,TS val 3624190684 ecr 2940665232], length 1448
13.640911 IP theirsite.37999 > mysite.https: Flags [.E], ack 30755, win 515, options [nop,nop,TS val 2940665331 ecr 3624190684], length 0
13.640976 IP mysite.https > theirsite.37999: Flags [.EW], seq 30755:32203, ack 627, win 506, options [nop,nop,TS val 3624190783 ecr 2940665331], length 1448
13.740069 IP theirsite.37999 > mysite.https: Flags [.E], ack 32203, win 526, options [nop,nop,TS val 2940665430 ecr 3624190783], length 0
13.740153 IP mysite.https > theirsite.37999: Flags [.EW], seq 32203:33651, ack 627, win 506, options [nop,nop,TS val 3624190882 ecr 2940665430], length 1448
13.839252 IP theirsite.37999 > mysite.https: Flags [.E], ack 33651, win 537, options [nop,nop,TS val 2940665530 ecr 3624190882], length 0
13.839316 IP mysite.https > theirsite.37999: Flags [.EW], seq 33651:35099, ack 627, win 506, options [nop,nop,TS val 3624190981 ecr 2940665530], length 1448
13.938391 IP theirsite.37999 > mysite.https: Flags [.E], ack 35099, win 549, options [nop,nop,TS val 2940665629 ecr 3624190981], length 0
13.938444 IP mysite.https > theirsite.37999: Flags [.EW], seq 35099:36547, ack 627, win 506, options [nop,nop,TS val 3624191080 ecr 2940665629], length 1448
14.037553 IP theirsite.37999 > mysite.https: Flags [.E], ack 36547, win 560, options [nop,nop,TS val 2940665728 ecr 3624191080], length 0
14.037618 IP mysite.https > theirsite.37999: Flags [.EW], seq 36547:37995, ack 627, win 506, options [nop,nop,TS val 3624191179 ecr 2940665728], length 1448
14.137132 IP theirsite.37999 > mysite.https: Flags [.E], ack 37995, win 571, options [nop,nop,TS val 2940665827 ecr 3624191179], length 0
14.137200 IP mysite.https > theirsite.37999: Flags [.EW], seq 37995:39443, ack 627, win 506, options [nop,nop,TS val 3624191279 ecr 2940665827], length 1448
14.236282 IP theirsite.37999 > mysite.https: Flags [.E], ack 39443, win 583, options [nop,nop,TS val 2940665927 ecr 3624191279], length 0
14.236354 IP mysite.https > theirsite.37999: Flags [.EW], seq 39443:40891, ack 627, win 506, options [nop,nop,TS val 3624191378 ecr 2940665927], length 1448
14.335398 IP theirsite.37999 > mysite.https: Flags [.E], ack 40891, win 594, options [nop,nop,TS val 2940666026 ecr 3624191378], length 0
14.335459 IP mysite.https > theirsite.37999: Flags [.EW], seq 40891:42339, ack 627, win 506, options [nop,nop,TS val 3624191477 ecr 2940666026], length 1448
14.434551 IP theirsite.37999 > mysite.https: Flags [.E], ack 42339, win 605, options [nop,nop,TS val 2940666125 ecr 3624191477], length 0
14.434616 IP mysite.https > theirsite.37999: Flags [.EW], seq 42339:43787, ack 627, win 506, options [nop,nop,TS val 3624191576 ecr 2940666125], length 1448
14.533722 IP theirsite.37999 > mysite.https: Flags [.E], ack 43787, win 617, options [nop,nop,TS val 2940666224 ecr 3624191576], length 0
14.533789 IP mysite.https > theirsite.37999: Flags [.EW], seq 43787:45235, ack 627, win 506, options [nop,nop,TS val 3624191676 ecr 2940666224], length 1448
14.632926 IP theirsite.37999 > mysite.https: Flags [.E], ack 45235, win 628, options [nop,nop,TS val 2940666323 ecr 3624191676], length 0
14.632993 IP mysite.https > theirsite.37999: Flags [.EW], seq 45235:46683, ack 627, win 506, options [nop,nop,TS val 3624191775 ecr 2940666323], length 1448
14.732801 IP theirsite.37999 > mysite.https: Flags [.E], ack 46683, win 639, options [nop,nop,TS val 2940666422 ecr 3624191775], length 0
14.732857 IP mysite.https > theirsite.37999: Flags [.EW], seq 46683:48131, ack 627, win 506, options [nop,nop,TS val 3624191875 ecr 2940666422], length 1448
14.831963 IP theirsite.37999 > mysite.https: Flags [.E], ack 48131, win 650, options [nop,nop,TS val 2940666522 ecr 3624191875], length 0
14.832026 IP mysite.https > theirsite.37999: Flags [.EW], seq 48131:49579, ack 627, win 506, options [nop,nop,TS val 3624191974 ecr 2940666522], length 1448
14.931211 IP theirsite.37999 > mysite.https: Flags [.E], ack 49579, win 662, options [nop,nop,TS val 2940666621 ecr 3624191974], length 0
14.931297 IP mysite.https > theirsite.37999: Flags [.EW], seq 49579:51027, ack 627, win 506, options [nop,nop,TS val 3624192073 ecr 2940666621], length 1448
15.030409 IP theirsite.37999 > mysite.https: Flags [.E], ack 51027, win 673, options [nop,nop,TS val 2940666721 ecr 3624192073], length 0
15.030478 IP mysite.https > theirsite.37999: Flags [.EW], seq 51027:52475, ack 627, win 506, options [nop,nop,TS val 3624192172 ecr 2940666721], length 1448
15.129575 IP theirsite.37999 > mysite.https: Flags [.E], ack 52475, win 684, options [nop,nop,TS val 2940666820 ecr 3624192172], length 0
15.129632 IP mysite.https > theirsite.37999: Flags [.EW], seq 52475:53923, ack 627, win 506, options [nop,nop,TS val 3624192271 ecr 2940666820], length 1448
15.228699 IP theirsite.37999 > mysite.https: Flags [.E], ack 53923, win 696, options [nop,nop,TS val 2940666919 ecr 3624192271], length 0
15.228766 IP mysite.https > theirsite.37999: Flags [.EW], seq 53923:55371, ack 627, win 506, options [nop,nop,TS val 3624192371 ecr 2940666919], length 1448
15.327877 IP theirsite.37999 > mysite.https: Flags [.E], ack 55371, win 707, options [nop,nop,TS val 2940667018 ecr 3624192371], length 0
15.327942 IP mysite.https > theirsite.37999: Flags [.EW], seq 55371:56819, ack 627, win 506, options [nop,nop,TS val 3624192470 ecr 2940667018], length 1448
15.427060 IP theirsite.37999 > mysite.https: Flags [.E], ack 56819, win 718, options [nop,nop,TS val 2940667117 ecr 3624192470], length 0
15.427128 IP mysite.https > theirsite.37999: Flags [.EW], seq 56819:58267, ack 627, win 506, options [nop,nop,TS val 3624192569 ecr 2940667117], length 1448
15.526297 IP theirsite.37999 > mysite.https: Flags [.E], ack 58267, win 730, options [nop,nop,TS val 2940667217 ecr 3624192569], length 0
15.526368 IP mysite.https > theirsite.37999: Flags [.EW], seq 58267:59715, ack 627, win 506, options [nop,nop,TS val 3624192668 ecr 2940667217], length 1448
15.625481 IP theirsite.37999 > mysite.https: Flags [.E], ack 59715, win 741, options [nop,nop,TS val 2940667316 ecr 3624192668], length 0
15.625552 IP mysite.https > theirsite.37999: Flags [.EW], seq 59715:61163, ack 627, win 506, options [nop,nop,TS val 3624192767 ecr 2940667316], length 1448
15.724607 IP theirsite.37999 > mysite.https: Flags [.E], ack 61163, win 752, options [nop,nop,TS val 2940667415 ecr 3624192767], length 0
15.724650 IP mysite.https > theirsite.37999: Flags [.EW], seq 61163:62611, ack 627, win 506, options [nop,nop,TS val 3624192866 ecr 2940667415], length 1448
15.823665 IP theirsite.37999 > mysite.https: Flags [.E], ack 62611, win 764, options [nop,nop,TS val 2940667514 ecr 3624192866], length 0
15.823717 IP mysite.https > theirsite.37999: Flags [.EW], seq 62611:64059, ack 627, win 506, options [nop,nop,TS val 3624192966 ecr 2940667514], length 1448
15.922871 IP theirsite.37999 > mysite.https: Flags [.E], ack 64059, win 775, options [nop,nop,TS val 2940667613 ecr 3624192966], length 0
15.922946 IP mysite.https > theirsite.37999: Flags [.EW], seq 64059:65507, ack 627, win 506, options [nop,nop,TS val 3624193065 ecr 2940667613], length 1448
16.022042 IP theirsite.37999 > mysite.https: Flags [.E], ack 65507, win 786, options [nop,nop,TS val 2940667712 ecr 3624193065], length 0
16.022113 IP mysite.https > theirsite.37999: Flags [.EW], seq 65507:66955, ack 627, win 506, options [nop,nop,TS val 3624193164 ecr 2940667712], length 1448
16.121191 IP theirsite.37999 > mysite.https: Flags [.E], ack 66955, win 798, options [nop,nop,TS val 2940667811 ecr 3624193164], length 0
16.121223 IP mysite.https > theirsite.37999: Flags [.EW], seq 66955:68403, ack 627, win 506, options [nop,nop,TS val 3624193263 ecr 2940667811], length 1448
16.220324 IP theirsite.37999 > mysite.https: Flags [.E], ack 68403, win 809, options [nop,nop,TS val 2940667911 ecr 3624193263], length 0
16.220371 IP mysite.https > theirsite.37999: Flags [.EW], seq 68403:69851, ack 627, win 506, options [nop,nop,TS val 3624193362 ecr 2940667911], length 1448

輸出中的標誌[E]和是Explicit Congestion Notifications。[W]``tcpdump

當您看到theirsite.36652 > mysite.https: Flags [.E]這意味著接收方檢測到鏈路擁塞並要求發送方（您的站點）放慢速度，並且發送方回應Flags [.EW]表示它已確認請求並減少了 TCP 視窗。

您可以像這樣禁用 ECN：sysctl -w net.ipv4.tcp_ecn=0

引用自：https://serverfault.com/questions/1089202