TCP stands for Transmission Control Protocol and is one of the core protocols of the Internet Protocol Suite. TCP complements the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP.

learn more… | top users | synonyms

0
votes
0answers
2 views

Connection interruptions on Debian router, possibly due to excessive duplicate ACKs?

I have a Debian server as a house router, which for a year has been working flawlessly. However, I recently moved and switched service providers from FiOS to Comcast, and possibly as a result am ...
6
votes
3answers
311 views

Why is my web server dropping connections with a TCP reset at high load?

I have a small VPS setup with nginx. I want to squeeze as much performance as possible out of it, so I've been experimenting with optimization and load testing. I'm using Blitz.io to do load testing ...
0
votes
0answers
23 views

Why would Windows 7 not complete this TCP handshake?

One of our customers is running Windows 7, and cannot reach some of our servers because it seems Windows 7 cannot complete a TCP handshake. Here's a packet trace to one our servers -- note that a SYN ...
1
vote
1answer
2k views

option http-server-close on HAProxy haproxy-1.5-dev19 will result in Connection: close header sent in response

I basically have the following issue: whenever I add option http-server-close to the haproxy config (either in frontend or backend section), haproxy will send a Connection: close header in the ...
1
vote
0answers
17 views

Spurious retransmission, Dup ACK and HTTP 408

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 ...
15
votes
4answers
72k views

What causes duplicate ACK records?

We're reviewing Wireshark captures from a few client machines that are showing multiple duplicate ACK records which then triggers retransmit and out-of-sequence packets. These are shown in the ...
-2
votes
0answers
31 views

How to prevent TCP retransmissions? [on hold]

I am using cURL to grab some data from websites. Some times (one out of ten) I get a time-out error from cURL but I am sure that the site is running (I can open it). In Wireshark I see TCP ...
3
votes
4answers
3k views

Need help troubleshooting intermittant TCP timeout in HAProxy

I have an application where the client connects to a server via a simple TCP based protocol over TLS/SSL. In development, this has worked great for many months while we were building our application ...
0
votes
1answer
912 views

How to increase nginx connections

I am facing the problem of nginx max connection issues. I am not able to increase max active connections(520) made by nginx. Some time it is using whole writing (516) operation connections. and due to ...
1
vote
0answers
19 views

Citrix NetScaler sending FIN, ACK for SSL VPN Clients

I realise that it's unlikely anyone here has a definite "Check this box to resolve this" answer, but I'm struggling with this issue and I'm hoping that someone with more knowledge than me can give me ...
0
votes
1answer
20 views

TCP Keepalive: Why does an idled ESTABLISHED connection end after 60 seconds, instead of tcp_keepalive_time?

I am investigating ways to mitigate a server against DoS-type attacks. In one scenario, I've opened several hundred TCP connections to my webserver. I do not send any data after the initial TCP ...
0
votes
0answers
12 views

Route only on output chain?

I have two machines A and B. I want to send iperf traffic from A to B, but first have it route through a userspace program on A. I did this with a tunneling device: therefore, I used the command ip ...
5
votes
1answer
5k views

Unexpectedly shrunk window

I run a major media upload/download site and I noticed these: Is this serious or background noise due to the big file sizes and is there any tweaks I can add to /etc/sysctl.conf to improve and ...
1
vote
1answer
995 views

How to reset a tcp connection immediately on both ends on a certain condition using linux netfilter/iptables?

Dear Serverfault community, I have the following problem: I need to reset (disconnect) tcp connections on both network sides immediately if a certain string is encountered in the packet data. I don't ...
1
vote
3answers
1k views

Windows Server 2008 - unable to bind any TCP port

OS: Win Server 2008 RC2 Windows firewall on (no effect when off) I have suddenly been plagued by an issue in which I cannot find any similar ones with a search. I am running about 20 game servers ...
0
votes
2answers
3k views

TCP port numbers reused and TCP Retransmission

Facing issues due to TCP Port Reuse and Retransmission for HTTP traffic. My deployment is as follows: enter image description here I have a squid proxy installed on a unix machine which is sending ...
0
votes
2answers
117 views

How to run Different congestion control algorithms in FEDORA 17?

I need to use different congestion control algorithms for tcp flow. How can I continue using those flow congestion algorithms from Fedora 11 in Fedora 17?
0
votes
0answers
19 views

SYN/ACK not received by iperf client?

I have an application that essentially consists of four components A, B, C, D. A and B are on the same machine - B and C are separate machines. Traffic is generated by an iperf client on A with a ...
4
votes
3answers
560 views

TCP sequence number

I would like to know if two segments of same sequence number arrive at the destination, which segment will get accepted ? For eg: A clients sends a packet to a server and wait for an ...
0
votes
3answers
2k views

Test a server using MTR through TCP

Is it possible to use MTR over TCP? If not is there an alternative? I have done some research and I am not finding any way to do such a thing, so I'm wondering if anyone has had any experience with ...
-1
votes
1answer
17 views

ufw status (what does the v6 stand for?)

My ufw status output looks like this: To Action From -- ------ ---- 22 ALLOW Anywhere 80/tcp ...
8
votes
0answers
79 views

SynProxy can not return syn ack packets with asymmetric dual bridge topology

I have a asymmetric dual bridge topology as shown below when i connect from 172.16.11.5 and 172.16.10.6 with ssh but i can not connect because of SynProxy. ------- ...
0
votes
0answers
27 views

Two processes stuck on network communication

We have had hang on our Oracle extraction process very intermittantly. Nothing obvious from the Oracle side, and starting to think it is more network related. There are two Oracle processes ...
1
vote
0answers
25 views

Debian limit number of TCP sockets for a process (especially tor) on OpenVZ

I have a debian 7.8 server, running on OpenVZ. On this server I'm running a tor relay and some other network services (like apache and mysql). However the tor service seems to eat up all my available ...
2
votes
0answers
19 views

Network sensor for a TCP connection for collecting statistics each second [closed]

I need a Network Sensor capable to gather basic end-to-end statistics (packet loss, jitter and network delay/RTT) of several TCP connections directed to the very same destination (ip-addr:port) on ...
23
votes
7answers
22k views

Why would a server not send a SYN/ACK packet in response to a SYN packet

Lately, we've become aware of a TCP connection issue that is mostly limited to mac and Linux users who browse our websites. From the user perspective, it presents itself as a really long connection ...
0
votes
5answers
9k views

netstat shows many times deploy.akamaitechnologies.com connected to my server

Many times, after running netstat on my server, I find one of IP addresses belonging to deploy.akamaitechnologies.com connected to my server, do someone has an idea on what is happening on my server ? ...
0
votes
0answers
13 views

rsyslog tcp packets containing multiple log messages

I have rsyslog receiving logs over udp and then relaying them over tcp to a load balance (nginx) which passes them along to SIEM collectors. The setup looks like this: network devices/appliances ...
-1
votes
0answers
7 views

delayed tcp fast retransmission

I operate some HLS servers based on Redhat Linux. I have a big problems. In streaming from HLS server to Client(smartphone), there are occurred some packet dropped. And then, Server received a lot of ...
1
vote
0answers
21 views

Should I disable the Nagle Algorithm for Outlook / Exchange RPC/HTTP communication?

I'm investigating reasons why several Outlook clients in non-cached mode are having delays communicating... resulting in Outlook hanging. My suspicion is that a Netscaler, or intermediate device (? ...
18
votes
3answers
11k views

What is the “in-the-wire” size of a ethernet frame? 1518 or 1542?

According to the table here, it says that MTU = 1500 bytes and that the payload part is 1500 - 42 bytes or 1458 bytes (<- this is actually wrong!). Now on top of that you have to add IPv4 and UDP ...
2
votes
1answer
924 views

How to force use of tcp instead of udp for rpcbind?

I'm trying to use tcp/111 for rpcbind under Debian Wheezy instead of udp/111. The portmap in Squeeze uses tcp/111 without any special configuration, but Wheezy fails. Even numerous sites (as well as ...
-1
votes
1answer
28 views

Can TCP be used like UDP by simply not sending ACK?

Assuming both client & server cooperated, could you emulate the functionality of UDP by not sending ACK packets, and not sending retransmissions? Or would most routers somehow bork the process if ...
0
votes
0answers
31 views

SSH stalled after a while

I am executing some commands over SSH from a linux client (centos 7) toward a server (wind river linux) and for a reason it always stopped ( not completed ). If i executed a command that take short ...
0
votes
1answer
23 views

REDSOCKS goes 'out of file descriptors' when trying to redirect all outgoing (TCP) traffic from my Linux machine

I'm trying to redirect all outgoing TCP traffic from my linux box to the remote SOCKS5 proxy server. Currently I'm using the following rule in the OUTPUT chain: sudo iptables -t nat -A OUTPUT -p tcp ...
3
votes
1answer
1k views

How to achieve multiple NFS/TCP connections to the same server?

I'm trying to maximize the NFS/TCP bandwidth between a Linux client and a single NFS server over a 10Gbps link. Although each NFS mount has its own device (major/minor), everything comes down to a ...
1
vote
0answers
33 views

Web sites freeze after clicking link - unexplainable ACK packet

We have a sporadic problem accessing some internal links on websites. (Windows Firefox, Internet Explorer, Chrome) Behaviour On first clicking a link, the browser will load infinitely. The second ...
0
votes
0answers
29 views

How to properly configure security group at AWS?

I'm trying to reach my server's FTP-port by its Elastic IP. I've configured the security group as follows: Inbound Type Protocol Port Range Destination All traffic All All ...
0
votes
1answer
56 views

Private communications between AWS EC2 instances

I have three EC2 instances with elastic IPs. Each one contains a server. Each server needs that TCP ports 8181, 2181, 2888 and 3888 are opened on each machine. Each server should have the possibility ...
2
votes
0answers
596 views

No response to some SYN packets when timestamps are enabled

I have a TCP server listening on a machine ("the server") running Ubuntu 12.04.3 (kernel 3.8.0-31-generic). It receives connections from 2 different client machines. Machine A is running Ubuntu ...
0
votes
1answer
1k views

ffmpeg simple RTMP streaming

I am trying to launch up a rtmp transcoder server using ffmpeg; that receives udp MPEG-TS streams as input, transcodes it; and generates an rtmp output to a URL, that can be accessed by users to ...
-2
votes
1answer
35 views

TCP - MSS option and different payload

This is a tcpdump from servers side. In line 1 i see MSS=1400. Why server sent in line 6 a packet of 4230 bytes when client want max 1400?
7
votes
0answers
84 views

How does server-side `TIME_WAIT` really work?

I know there are quite a few SE questions on this, and I believe I read as many of them as it matters before coming to this point. By "server-side TIME_WAIT" I mean the state of a server-side socket ...
13
votes
7answers
2k views

Why is it good practice to compare checksums when downloading a file?

Websites which supply ISO files for download will often give the md5 checksums of those files, which we can use to confirm that the file has downloaded correctly, and has not been corrupted. Why is ...
8
votes
2answers
242 views

Extreme UDP packet loss at 300Mbit (14%), but TCP > 800Mbit w/o retransmits

I have a linux box I use as the iperf3 client, testing 2 identically equipped Windows 2012 R2 server boxes with Broadcom BCM5721, 1Gb adapters (2 ports, but only 1 used for the test). All machines are ...
0
votes
1answer
335 views

Effects of IW10 (initcwnd 10 initrwnd 10) on high speed LAN based TCP/IP communications?

What does changing the number of packets sent during the initial congestion window to 10 have on LAN connections? Via: ip route change default via GATEWAY dev INTERFACE initcwnd 10 initrwnd 10 Is ...
0
votes
1answer
21 views

Upgrading Web Application's Systems' Kernels for IW10 & other related improvements - upgrade all machines? LB first? Most important?

Stackers - We're making the push to upgrade the systems for our web app to take advantage of the various TCP improvements becoming more readily available (e.g. ...
3
votes
1answer
162 views

Common back pressure strategies for services under sustained high load

I'm wondering what are the common backpressure strategies people use for their web services? Imagine your service operates under heavy load, and at some point the load reaches 120% of your capacity. ...
2
votes
1answer
52 views

Outgoing packet has NATed src address

Configuration/Topology: There are 3 machines hadoop2 | hadoop | driver eth0 10.10.15.3 | eth0 10.10.15.2 | tap0 192.168.0.199 ...
1
vote
1answer
49 views

No response to TCP SYN packet when padding is not 0's or F's

I have this client which initiates a 3 way handshake with a SYN packet but there is no SYN ACK response. We figured out that it was because the client did not pad the end of the TCP headers with 0's ...