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.

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TCP Window Scaling Problem over MPLS

After extensive troubleshooting why the TCP speed over an MPLS circuit is slow in one direction, I figured out that by adjusting the TCP window size the situation improved a lot. Maybe you can tell me ...
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403 views

TCP congestion collapse

I am experiencing suboptimal performance on an EC2 instance connecting to an RDS instance. This particular instance was built before VPC's existed, so all the traffic is flowing through a single ...
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580 views

TCP connection stuck in SYN_RECV state despite ACK received

My client and server are both internal machines. tcpdump on both client and server show all three parts of handshake are communicated, however netstat on server shows SYN_RECV, and on client shows ...
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434 views

snmp MIB-TCP::tcp not showing any usage

I am trying to configure MRTG on all of my servers for making a network weathermap, this requires running SNMP which MRTG gets the information from. So, I installed it on two servers the exact same ...
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40 views

TCP buffer sizes and ethernet bonding

(This question was originally posted on stack overflow; Andy told me that I could get faster help here, so it is re-posted here now.) I am experimenting with TCP buffer size tuning on Linux, but ...
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79 views

Does Fast Retransmit and Retransmission Timer work at the same time?

When Fast Retransmit is implemented, if I received packet 1, then I will send an ACK that says I need packet 2, and then if I received packet 3, I will send a duplicate ACK that says that I need ...
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736 views

What does “connections reset due to unexpected data” in netstat -s mean

I'm running a memcached server under heavy load from multiple web servers. While investigating some odd app level behaviour, we spotted that netstat -s on the memcached box was showing a lot of ...
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739 views

TCP connections in FIN-WAIT-2 state on linux not timing out according to tcp_fin_timeout

We run a service with lots of embedded devices in the field, their tcp stack is a bit buggy and sometimes does not close connections properly, resulting in some connections being stuck in FIN-WAIT-2 ...
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9k views

ksoftirqd process overloads CPU with high-bandwidth and multiple network connections

I got a 10GBit Server with proxmox 2.1 installed. There's an OpenVZ container running with Ubuntu 10.04 64bit. I can get 200-300MB/sec with wget from data-center internal servers (-O /dev/null) which ...
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32 views

TCP Handshake fails when ICMP Redirects are enabled

So it seems that due to ICMP redirects it's not possible to connect to a server behind a VPN connection. It immediately responds with a TCP RST (with manifests itself in SSH as ...
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113 views

How to change tcp's window size?

I've tried changing the tcp's window size by modifying net.ipv4.tcp_wmem and net.ipv4.tcp_rmem values, however the changes which I make have no effect on actual window size which I can check using a ...
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142 views

Why is SQL Server using all ephemeral ports connecting to itself and causing TIME_WAITs?

I've got an AWS server with Windows 2008 R2, SQL Server 2012, and Tomcat 7. When I run netstat -ano the screen is flooded with TIME_WAIT. I posted the output in a Gist. When I run CurrPorts, filter ...
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105 views

Linux - Outgoing connections from process timeout after the process restarts

banging my head against the wall with this one... I have an Ubuntu Linux server, on top of which our own process which holds 40K persistent connections to external services. When the process ...
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639 views

TCP Connection Issue Between Linux Machine and VMWare Windows Server

I have a TCP connection issue as follows. The setup: VMWare Virtual Machine: Windows Server 2008 R2 DataCenter SP1, IP: 192.168.2.111, DG: 192.168.2.254 Host Machine: Windows 7 Professional SP1, IP: ...
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841 views

TCP connection timeouts that persist - listener queue backlog?

I have an app running on AIX 6.1 that has a single server process that listens for and polls tcp connections and simply forwards on messages to another process using an IPC message queue. It's been ...
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996 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 ...
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1k views

Should I set rto_min for a route inside data center?

We have a few dedicated server rented in a data center with debian 7, kernel 3.2. We use one of those servers as a database server. The network between our application server and database server is ...
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959 views

mysql client can't read query result?

So I have this machine running an XMPP server which connects to its MySQL database. When I start load-testing it, all goes fine up until after about 500s when I notice: Caused by: ...
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296 views

what can put linux process managing connection pool into bad state, so it restarts them continously?

I have an application with pool of connections to MySQL. At some point, in production, every 1-3 seconds some socket is closed. As a result my app restarts this connection. This is pretty big pool ...
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149 views

Tcp window size won't go above 130048

I have 2 servers set up with about 80ms latency between them. Both are centos 6 and run a java app that transfers data from on location to another. Both are on 1gbps connections. I have been trying ...
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648 views

haproxy tcp transparent mode on the same box as service

I'd like to set up transparent HA Proxy for TCP protocol. It works flawlessly when HA Proxy is in front of the boxes that are running the service. But when I try to set up HA Proxy in transparent mode ...
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361 views

A tool to measure overhead of establishing TCP connections

I need a tool which would while doing port forwarding measure how much time was spent establishing TCP connections vs total time passed. Charles debugging proxy has the port forwarding feature and ...
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1k views

In Windows 2008R2 there is a TCP port that is stuck LISTENING but the process that has it open is terminated?

I have a program, NC_net that allows Nagios to monitor Windows machines for various metrics and it seems to have caused a sporadic issue where when the service stops, the TCP port remains open. The ...
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42 views

Nginx log to syslog on TCP port

I need to redirect Nginx access and error logs to a remote syslog server. From http://nginx.org/en/docs/syslog.html I saw that I can do: error_log syslog:server=192.168.1.1; However I need to ...
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13 views

TCP tuning for DPM on Windows 2012

I've got a pair of servers on opposite ends of a fast (1-10Gb depending on the server) but higher latency (40-60ms) link. Various network tuning options have been set resulting in iperf3 yielding ...
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18 views

Measure goodput before sending a response

My idea is to make it possible for web applications working on slower connections to fallback on alternative smaller asset versions(like images, videos, etc.). HTTP Live Streaming has similar behavior ...
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46 views

Server socket sitting in FIN_WAIT_1 whilst network doesn't see its traffic

We've been trying to get a grip on a really weird problem where we can wget a page from Apache 2.2.19 on solaris 10 and some permutations of requests reliably take various fixed lengths of time to ...
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20 views

Iperf Tcp Client and Server

I'd really like to know why the bandwith in the client is higher than the server, i can´t find the answer explaining why this happens. Thank you, Tiago Melancia Values of the bandwidth: Client ...
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45 views

Can iptables log all type of tcp connection?

Can iptables log tcp Split-Handshake and Simultaneous-Open connections as well as tcp Three Way Handshake? Here is these two kind of tcp connection descriptions. Here I find how to log new tcp ...
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141 views

Apache timeouts and TCP retransmission

The documentation for the timeout directive in apache states that: When writing data to the client, the length of time to wait for an acknowledgement of a packet if the send buffer is full. But ...
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28 views

Why might a connection stay in TIME_WAIT for hours or even days?

Our environment is ubuntu 12.04 on EC2. I know TIME_WAIT is a good thing, and I know generally it's OK to see connections remain in TIME_WAIT for up to 2 minutes according to all the reading I've ...
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46 views

TCP Syn cookies is it always turned on when enabled?

For Linux kernel 2.6.32 if I set net.ipv4.tcp_syncookies = 1 will that be always used or only during a SYN flood attack? I found 2 sources which says the opposite. 1: "There are, however, two ...
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89 views

Wireshark RST against TCP Zero Window

During application sharing with Microsoft Lync Client (Mac OS X), TCP ACK with RST flag is sent from my application end to Lync end against TCP Zero Window packets and call gets dropped. Image Link. ...
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134 views

tcp previous segment not captured when NAT

I have a client request web service on a server behide NAT. My client IP is 10.54.10.193 NAT address: 10.54.28.183 Server address: 62.209.39.203 When client request web service on server we have TCP ...
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139 views

Inconsistency in TCP and HTTP connection management

I observe following scenario in WireShark: The problem I see here is that after receiving [FIN, ACK] from server (4090) and acknowledging it (4092), http client attempts to send another HTTP ...
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72 views

What exactly constitutes a bad TCP segment?

What constitutes a bad segment as in bad segments received in the netstat output below? I would think a TCP header's checksum could do it, but are there other things? If a segment arrives after its ...
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27 views

What technology do data center use to guarantee low RTT?

I was reading about data-center-tcp DCTCP and the paper was talking about the low retransmission timer (RTT) of about 250µs, but didn't state how that is being done. Somewhere else I read that DCTCP ...
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77 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 ...
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262 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 ...
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91 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 ...
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95 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 (? ...
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100 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 ...
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506 views

Nginx TCP Fast Open Issue

I have configured Nginx and Apache on one of my servers. The nginx server listens on port 80 and Apache on port 81. Nginx works as a reverse proxy. In nginx I configured TCP Fast Open: server { ...
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157 views

What happens if a machine gets a SYN/ACK packet without sending initial SYN packet?

I'm thinking of a situation where an attacker manipulates a SYN packet that was sent from A's source IP address to B. The server will receive the packet and think it's a legitimate packet, and send a ...
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25 views

How do I cap each individual tcp stream, to a fixed maximum rate?

I've read but not in depth all the various traffic shaping docs and seen the long question on HSFC scheduling Does anyone really understand how HFSC scheduling in Linux/BSD works? looked at the ...
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249 views

TCP High Send-q coupled with FIN_WAIT1 status

I'm having a problem with one of my webservers, which is taking minutes to completely render a web page. I had a look at the TCP connection and noticed that I have a very high value in the send-q ...
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677 views

tcp connection reset [RST, ACK]

getting this errors looks like server is restating the connection because of some packet loss any possible suggestion's to figure out this 37713 591.925575000 ...
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34 views

Split TCP packet - Data layer vs IPv4Layer

What is the different between split TCP packet in the Data layer compare to split the packet in IPv4Layer ?
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1k views

HAProxy resetting backend connections

I'm in the process of setting up a series of servers as proxies to our application server, primarily to obscure the application server's IP as part of a suite of anti-DDOS measures. My goal is to ...
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573 views

Always keep socat alive

I have a socat running nicely, executing my command when a connection comes in with the arguments provided. However, the issue I am having is that the socket is at EOF and the next time a connection ...