TCP连接; 未收到ACK

我无法从Linux发送邮件到Exchange服务器。 当我从端口25从Linux telnet到Windows时，我没有收到来自Exchange的任何消息。 等待几秒钟后连接自动终止。

使用tcpdump我可以看到，Windows持续发送SYN + ACK，并最终closures连接。 即使Linux响应ACK消息，Windows也不会看到它。 如果我发送一些消息（远程logintesting）而不等待Exchange的“问候语”，则连接工作。

我已经validation了Windows防火墙，并且允许来自Linux机器的连接，并且我在防火墙日志中找不到任何数据包丢弃消息。

从Windows到Linux端口25的连接工作正常。

• nfs-kernel-server在Ubuntu中保持失败
• Monit“检查程序”并根据退出码重新启动
• 当g + w在用户的主目录上时，请允许ssh
• IBM System x3850 M2 Ubuntu服务器安装
• 可以在两个不同的独立域之一中识别和validationldap用户？

细节：

Windows：xxx243 / 255.255.255.128; 网关= xxx129

Linux：xxx145 / 255.255.255.128; 网关= xxx129

Linux到Windows tcpdump

root@yy01:~# tcpdump -nni eth0 host xxx243 and port 25 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes 05:03:58.846266 IP xxx145.45104 > xxx243.25: Flags [S], seq 3228055127, win 29200, options [mss 1000,sackOK,TS val 659649138 ecr 0,nop,wscale 7], length 0 05:03:58.849071 IP xxx243.25 > xxx145.45104: Flags [S.], seq 37978062, ack 3228055128, win 8192, options [mss 1460,nop,wscale 8,sackOK,TS val 316999749 ecr 659649138], length 0 05:03:58.849097 IP xxx145.45104 > xxx243.25: Flags [.], ack 1, win 229, options [nop,nop,TS val 659649139 ecr 316999749], length 0 05:04:01.858960 IP xxx243.25 > xxx145.45104: Flags [S.], seq 37978062, ack 3228055128, win 8192, options [mss 1460,nop,wscale 8,sackOK,TS val 317000050 ecr 659649138], length 0 05:04:01.859001 IP xxx145.45104 > xxx243.25: Flags [.], ack 1, win 229, options [nop,nop,TS val 659649891 ecr 316999749], length 0 05:04:07.874811 IP xxx243.25 > xxx145.45104: Flags [S.], seq 37978062, ack 3228055128, win 65535, options [mss 1460,sackOK,TS val 317000651 ecr 659649138], length 0 05:04:07.874872 IP xxx145.45104 > xxx243.25: Flags [.], ack 1, win 229, options [nop,nop,TS val 659651395 ecr 316999749], length 0 05:04:19.875384 IP xxx243.25 > xxx145.45104: Flags [R], seq 37978063, win 0, length 0 

Linux向Windows tcpdump发送一些数据而不用等待问候

 root@yy01:~# tcpdump -nni eth0 host xxx243 and port 25 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes 05:06:30.521152 IP xxx243.25 > xxx145.45234: Flags [R], seq 1489851708, win 0, length 0 05:06:31.253677 IP xxx145.45246 > xxx243.25: Flags [S], seq 3514263924, win 29200, options [mss 1000,sackOK,TS val 659687240 ecr 0,nop,wscale 7], leng th 0 05:06:31.256475 IP xxx243.25 > xxx145.45246: Flags [S.], seq 3020263353, ack 3514263925, win 8192, options [mss 1460,nop,wscale 8,sackOK,TS val 317014 989 ecr 659687240], length 0 05:06:31.256520 IP xxx145.45246 > xxx243.25: Flags [.], ack 1, win 229, options [nop,nop,TS val 659687241 ecr 317014989], length 0 05:06:34.255733 IP xxx243.25 > xxx145.45246: Flags [S.], seq 3020263353, ack 3514263925, win 8192, options [mss 1460,nop,wscale 8,sackOK,TS val 317015 289 ecr 659687240], length 0 05:06:34.255782 IP xxx145.45246 > xxx243.25: Flags [.], ack 1, win 229, options [nop,nop,TS val 659687990 ecr 317014989], length 0 05:06:36.720344 IP xxx145.45246 > xxx243.25: Flags [P.], seq 1:3, ack 1, win 229, options [nop,nop,TS val 659688607 ecr 317014989], length 2: SMTP: 05:06:36.924198 IP xxx145.45246 > xxx243.25: Flags [P.], seq 1:3, ack 1, win 229, options [nop,nop,TS val 659688658 ecr 317014989], length 2: SMTP: 05:06:37.176212 IP xxx145.45246 > xxx243.25: Flags [P.], seq 1:3, ack 1, win 229, options [nop,nop,TS val 659688721 ecr 317014989], length 2: SMTP: 05:06:37.680210 IP xxx145.45246 > xxx243.25: Flags [P.], seq 1:3, ack 1, win 229, options [nop,nop,TS val 659688847 ecr 317014989], length 2: SMTP: 05:06:38.688207 IP xxx145.45246 > xxx243.25: Flags [P.], seq 1:3, ack 1, win 229, options [nop,nop,TS val 659689099 ecr 317014989], length 2: SMTP: 05:06:40.271716 IP xxx243.25 > xxx145.45246: Flags [S.], seq 3020263353, ack 3514263925, win 65535, options [mss 1460,sackOK,TS val 317015890 ecr 659687240], length 0 05:06:40.271765 IP xxx145.45246 > xxx243.25: Flags [.], ack 1, win 229, options [nop,nop,TS val 659689494 ecr 317014989], length 0 05:06:40.708211 IP xxx145.45246 > xxx243.25: Flags [P.], seq 1:3, ack 1, win 229, options [nop,nop,TS val 659689604 ecr 317014989], length 2: SMTP: 05:06:44.748217 IP xxx145.45246 > xxx243.25: Flags [P.], seq 1:3, ack 1, win 229, options [nop,nop,TS val 659690614 ecr 317014989], length 2: SMTP: 05:06:44.751495 IP xxx243.25 > xxx145.45246: Flags [P.], seq 1:93, ack 3, win 65533, options [nop,nop,TS val 317016338 ecr 659690614], length 92: SMTP: 220 EXxx.yyyy.local Microsoft ESMTP MAIL Service ready at Thu, 4 Feb 2016 05:06:44 +0100 

请告知这个问题的可能原因。

注意：我在stackoverflow上问过同样的问题，他们build议在这里问一下。

谢谢，