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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What could be the cause for outbound TCP/IP traffic beeing blocked while ICMP is still working?

On a Windows Server 2003 there is a strange issue. Every 6 hours the server don't accept outbound TCP/IP traffic while inbound traffic working fine. If the problem occurs I can connect with RDP to ...
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1answer
431 views

Is it fine to turn off tcp window scaling and tcp timestamps on server?

Our application is running on Amazon server and we were continuously facing the issue related to tcp handshaking. Sometimes we were not able to connect to our application or telnet on port 80 of our ...
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1answer
90 views

How do I know that my TCP connection is safe from the Firewalls/NAT?

Being on the Azure cloud, I found that the firewalls there drop connections between the Web server and the database quite often. Mostly when there was some inactivity, I think something between 5 and ...
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1answer
237 views

TCP Duplicate Acks are received

We are trying to get to maximum throughput on ftp over an LTE link. When we are downloading a file using ftp some duplicate ACKs are seen. Reading about the duplicate ACKs, I gather they are sent so ...
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1answer
1k views

How to capture retransmitted packet info with tcpdump?

TCP retransmission rate on a host are often a good indicator of network problems. How do I find out the source and destination IPs for the packets that are being retransmitted? For context, on hosts ...
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2answers
45 views

Three Duplicate acknowledgements

I understand the process of congestion avoidance where you trying to control the level of congestion in a network, and avoid loss of packets. But how can there be three acknowledgements, even if one ...
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1answer
910 views

Reverse proxy for mixed tcp, udp, and http services

I'm building an architecture that will be hosting various services which individually maybe listening on a variable number of ports that could be mixed protocols. I want to map these services to ...
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3answers
9k views

Excessive 'TCP Dup ACK' & 'TCP Fast Retransmission' causing issues on network. What's causing this?

I'm getting excessive TCP Dup ACK and TCP Fast Retransmission on our network when I transfer files over the MetroEthernet link. The two sites are connected by one sonicwall router, so the sites are ...
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1answer
672 views

HTTP, TCP, UDP and connectionless

I am a bit confused with HTTP lately. Some facts are that TCP can operate connection orientated or connectionless, this I understand. TCP though is connection-oriented while UDP is connectionless ...
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2answers
2k views

How can I take advantage of IW10 in kernel 2.6.33?

I've read that 2.6.33+ allows setting custom cwnd. if the IW is 10 by default (for all distros? only some?) how does one view what the current IW is on a particular compiled kernel? references: ...
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1answer
922 views

HTTP 502 Bad Gateway error response

I'm debugging an issue and running out of ideas. I have a server with SharePoint code hosted at port 8080 and a WCF REST service at port 8801. From another machine on the domain, I can connect to the ...
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0answers
255 views

XenServer open vSwitch performance downgrade

I'm trying to capture part of an inter hypervisor traffic between 2 virtual machines running over XenServer 6.2. I want to mirror some TCP sessions to a 3rd virtual machine with minimum affect to the ...
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1answer
1k views

pfSense routing between two routers with shared network

I have a network set-up using two pfSense routers arranged like this:- DMZ1 WAN1 WAN2 DMZ2 | | | | | | | | \___ PF1 PF2___/ | ...
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0answers
56 views

Throughput decreases after MTU 5000

I am trying to test throughput between two computers directly connected through 1 Gb and testing with iperf. I am getting a throughput around 980Mbps when MTU is between 5000 and 5050, however it ...
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1answer
28k views

What does “net_ratelimit: 44 callbacks suppressed” mean on a linux based router?

I'm trying to tune Snort performance on a Debian based router. I was seeing stuff like: snort packet recv contents failure: No buffer space available So I upped the buffers to 8M and when that ...
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1answer
817 views

Dropped ACK FIN, ACK RST, RST packets on webserver with iptables

I run a webserver (Apache) on a Debian 7 machine, with iptables on the same machine. iptables rules are generated by the ConfigServer Firewall (CSF) script. The websites hosted there are fine on my ...
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1answer
633 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 ...
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1answer
333 views

rmem_max more than rmem_default

I just installed centos 6.3 freshly and noticed the following: [root@localhost user1]# cat /etc/redhat-release CentOS release 6.3 (Final) [root@localhost user1]# [root@localhost user1]# cat ...
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1answer
525 views

How to find source of TCP failed connection attempts? [closed]

I've got a host that has experienced a sudden increase in the rate of failed TCP connections. It's gone from something like 0.3/sec to 1.5/sec. Regardless of the severity of my particular issue, ...
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2answers
64 views

Is recipient's MAC address necessary for TCP connections across the internet? [closed]

I want to estabilish TCP connection over the internet between 2 computers which are in different local networks (the local networks use wifi). I have looked for description of TCP protocol, ...
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0answers
73 views

Tomcat fails to return syn requests to F5

I have an F5 LTM sitting in front of two tomcat servers which host 4 applications. When I initially create the pools and add the members to the LTM I can hit all applications. This is the weird part, ...
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3answers
76 views

How many packets will it take to send particular data?

If I know the maximum packet size is 1500 bytes say for Ethernet frame v2 then for example I want to transfer 1 KB over the Internet which is roughly 1024 bytes. Will the packet be split into many ...
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3answers
4k views

Why is UDP slower than TCP on Ubuntu Server?

I transfer data between two Ubuntu Servers (12.04) via iperf on 1Gb LAN. iperf -s <-> iperf -c <addr> -n2G TCP speed = 925 Mbits/sec iperf -su <-> iperf ...
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2answers
377 views

Clustering TCP servers, so can send data to all clients

I'm developing a real-time mobile app by setting up a TCP connection between the app and server backend. Each user can send messages to all other users. (I'm making the TCP server in Python with ...
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1answer
118 views

TCP packet filter based on TCP sequence

I need to build a test environment with a very precise packet loss based on specific TCP sequence or, optionally, on payload content. I couldn't figure out how to do it with tc or iptables. What tool ...
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1answer
44 views

Off-loading HTTP traffic

Need help in off loading HTTP traffic. My web server is having a lot of traffic resulting in slow response. It is also getting requests on port 80 from various mobile applications too. Traffic from ...
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1answer
407 views

Troubleshoot Broken TCP From OpenVPN Client To Server; But ping, traceroute Work

I'm troubleshooting an OpenVPN Server setup on OS X Mavericks. Prior to the 10.9 upgrade, this all worked, and I'm trying to isolate the problem to something fundamental or my server/client setup. ...
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2answers
104 views

Network In greater than Network Out?

Stat Image: http://carzz.co/network.png Running a small image website on EC2 without much traffic to speak of (800 user sessions per day). In looking at the EC2 Monitoring on the newly created ...
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2answers
194 views

MySQL connection errors when client server bandwidth is exhausted

I have several servers with a lot of outgoing traffic using nginx. When the bandwidth is exhausted (1Gbit), I have problems connecting to my mysql server from those servers. The connect always fails ...
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1answer
4k views

Root cause of “curl: (56) SSL read: errno -5961” errors

I was evaluating some SSL failures, and noticed that when I use curl to one of the failing sites, I got curl: (56) SSL read: errno -5961; however, my google queries for that error didn't show the ...
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1answer
184 views

How does a file get sent over an HTTP connection? [closed]

A teacher of mine says when you are browsing a web server such as apache2 that has file/directory listing enabled then it secretly opens an ftp server to transfer the file. This confuses me, though ...
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1answer
164 views

Oracle 11g TNSLSNR LAST_ACK connection flooding

We have Windows 2k3 EE SP2 with Oracle 11.2.0.1.0 DB installed. The DB is used by different applications (including web-apps and services). From time to time, we have some problems with the web ...
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1answer
122 views

TCP 443 Connection goes into server but never reaches Apache2 (Passenger)

We have some weird problems, when external servers try to connect to our Website on Port 443(TCP) which is an Apache2+Passenger and a Rails Application. The problem only happens rarely. I started to ...
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2answers
215 views

VMWare NAT releasing SYN packets from guest but not admitting SYN/ACK packets to guest

VMWare Server 2.0.2 Host OS is Windows Server 2008 R2 Standard Guest OS is Windows XP I am using VMWare VMNet8, the NAT network. The VM guests can't see out to the network around the VM host. Packet ...
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1answer
372 views

problems simulating TCP SYN flood

I'm trying to simulate a TCP SYN flood to tune a web server (planning to deploy on AWS). I setup a 'target' VM, disabled iptables and running hping (hping -p 80 -i u1000 -c 1000 -S destaddr) from ...
2
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1answer
190 views

Simulate tcp disconnect using socat

I am trying to use socat command to simulate a tcp disconnect between my client service and EMS broker process on a remote host. I am running this socat command socat TCP-LISTEN:8123,fork ...
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2answers
195 views

once in a while windows / .net application ignores the tcp fin flag

i've run into a network problem which i cannot solve. on a few computers running windows 8.1 and communicating with linux http server tcp connections dangle on the windows side instead of being ...
29
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3answers
4k views

Tuning iSCSI storage

This is a Canonical Question about iSCSI we can use as a reference. iSCSI is a protocol that puts SCSI commands as payload into TCP network packets. As such, it is subject to a different set of ...
2
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1answer
2k views

tcpdump capturing tcp resets by host

I am trying to figure out where my tcp resets on my webserver happen. I have the following capture: tcpdump -fnni bond0:-nnvvS -w dump.pcap 'tcp[tcpflags] & (tcp-rst) !=0' When I look at the ...
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2answers
168 views

Optimizing OS for HTTP requests

We make a lot of HTTP requests. Recently, we've started thinking about optimizations at the OS level to make more requests from a single machine. In order to check the performance of our OS, I've ...
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1answer
92 views

TCP syn cookie calculation on Windows Server

Windows Server uses uses TCP syn cookies to protect itself from syn-flooding attacks. Is it known, how the operating system (Windows Server 2008 R2 and Windows Server 2012) calculates the syn cookie? ...
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1answer
499 views

How to enable/disable TCP DELAYED ACK parameter on SUSE linux?

I want to disable TCP DELAYED ACK parameter on SUSE Linux Enterprise Server for some performance tuning operations. I have used sysctl command but it does not list this parameter. also in SUSE ...
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0answers
131 views

How can i detect and diagnose local network problems on a multi-server environment?

I'm a software engineer who trying to detect (and solve if possible) weird local networking problems since 2 weeks on multi-server hosting environment. We bought 3 dedicated boxes with 32GB ram 8 ...
2
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1answer
92 views

How do you change tcp_congestion_control on OpenVZ?

I have a network of OpenVZ machines that I am testing various congestion control methods on. I need to know how to change the congestion control. Currently I get nothing but permission denied. Is it ...
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1answer
2k views

TCP: Treason uncloaked! shrinks window Repaired

I have this error. The server works fine but sendmail doesn't. I can't reach it for download emails but it sends them. I have this when I type dmesg: TCP: Treason uncloaked! Peer ...
9
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4answers
23k views

How do I make cURL use keepalive from the command line?

I'm trying to verify that HTTP persistent connections are being used during communication with a Tomcat webserver I've got running. Currently, I can retrieve a resource on my server from a browser ...
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6answers
15k 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 ...
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1answer
56 views

routed network, subnetwork clients has broken tcp connection

I manage a linux server which works also as a router, and route between following networks: PPPoE (to connect to ISP) (default gw) wired network 2x VPN networks (PPTP and openVPN) wireless AP (DHCP) ...
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1answer
60 views

Routing between two PC

I have two computers connected by wire directly: PC-1 ============= PC-2 PC-1 configuration: IP Address: 192.168.1.1 netmask: 255.255.255.0 PC-2 configuration: IP Address: 192.168.1.2 ...
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1answer
55 views

What packet to ignore to not have ssh terminated on brief connectivity loss?

It seems like sometimes there are some connectivity problems around the edge of our network to certain other networks, and my ssh sessions with some remote servers, which themselves have no ...