I have a server which serves as sms gateway (using kannel) and have multiple client connecting to it, but recently this one client with their particular IP said that they can't send to my server and so I checked on the http access log and it show that the said client getting below error
148:xx.xx.xx.xx - - [29/Jun/2015:18:08:04 +0800] "-" 408 -
296:xx.xx.xx.xx - - [29/Jun/2015:16:41:41 +0800] "-" 408 -
659:xx.xx.xx.xx - - [29/Jun/2015:16:57:22 +0800] "-" 408 -
983:xx.xx.xx.xx - - [29/Jun/2015:17:06:59 +0800] "-" 408 -
1143:xx.xx.xx.xx - - [29/Jun/2015:17:14:20 +0800] "-" 408 -
So I fired up tcpdump to check whether if it's our issue or the client and this what I see from our server and client server. I looked around for someone mentioned that my server is not receiving the ACK. I find it weird since the other client connection are not having the problem. The server are located behind a firewall (Sonicwall) but I don't see the firewall dropping any packet nor the netstat -i showing any dropped packet. I'm not well versed with networking and I am very much lost here but any help are very much appreciated. I can post any more details needed. THANKS!
