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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Squid3 CONNECT imap.gmail.com:993 TCP_DENIED:NONE

I have the following configuration under squid.conf. However, when my Blackberry email client attempts to fetch new emails, etc. Squid access log show the following error: imap.gmail.com "CONNECT ...
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1answer
101 views

Does TCP's MSS hide a mismatched intra-LAN MTU?

I'm trying to understand how mismatched MTUs behave in a network. Suppose two hosts are able to talk to each other through an Ethernet-based network. The network and host A are configured for jumbo ...
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1answer
417 views

what could cause a not so busy redis server to close connection?

We have 17k tcp connection in CLOSING state on redis server. My understanding is that only client would initiate closing a connection, not from a redis server. So I should see 0 connection in CLOSING ...
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2answers
226 views

TCP acks are paused, then resumed, then paused again. Why?

I would like some help finding the reason for the reduced data transfer rate in my application. I have 12 embedded systems and a Linux server. The embedded systems send data to the server over TCP on ...
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3answers
4k views

NAT Gateway - Maximum connection limit

I know just enough networking to be dangerous. The nitty gritty low level details of NAT are not something I am particularly knowledgeable about. I accidentally found myself in a discussion earlier ...
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1answer
274 views

how to determine client side or server side retransmission from a pcap

I am trying to get some clarification on something I read here: how to calculate packet loss from a binary TCPDUMP file The first answer says that the sequence number will be the same from client to ...
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0answers
123 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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1answer
86 views

How to artificially open many tcp connection on a host (testing)? [closed]

I'm trying to build a test setup which test my server's performance under high load. In order to do that I want to open thousands of tcp connection. The problem is that I only have two hosts, one is ...
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1answer
426 views

IIS listening 127.0.0.1 instead 0.0.0.0

I configure binding on my IIS 7 server like: ip address: All Unassigned port: 8080 but in netstat -aon command see only 127.0.0.1:8080 instead 0.0.0.0:8080(which I would like) (0.0.0.0:8080 is ...
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0answers
133 views

After sending Duplicate ack by the server, it stop responding [closed]

My TCP client communicates with multiple 3rd TCP servers. However one particular server produces duplicate ack and stop responding in the specific time only. That particular server is OK other time. I ...
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1answer
210 views

Low throughput on Debian + nginx/apache

On the same LAN/WAN I have a Windows server 2012 server running IIS 7.5 and a Debian (wheezy) server running Nginx 1.4.5. Both servers are connected to the same LAN/WAN. When I download a 10MB file ...
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1answer
148 views

How to filter for the most common problems with tcpdump/tshark

I am currently using the following command in Linux to get specifics on network problems. tshark -r file.pcap -q -z io,stat,1,\ "COUNT(tcp.analysis.retransmission) tcp.analysis.retransmission",\ ...
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1answer
48 views

TCP ACK Window shrinking

(Note: I am not a networking engineer) We are sending files to an outside vendor and getting random timeouts on different services. It seems that we are getting timeouts most often on larger files. We ...
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1answer
2k views
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1answer
67 views

FTP upload slows down when devices are connected via hub [closed]

I have a setup with a network hub and three Ethernet devices. One of them is a PC (running windows XP), two others are hardware components that need to communicate with each other over the network. ...
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1answer
1k views

Windows Server 2012, application needs administrative access to open port

How can I grant an application access to listen on one particular port, without running it as Administrator or disabling UAC? Per policy, had to transition from an old server (Windows Server 2003) to ...
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0answers
22 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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2answers
4k views

TCP Dump, cannot understand these 4 lines?

I need support understanding these 4 lines. looks like tcp dump but im actully not understanding what exactly is happening here. 13:13:22.407445 IP 192.168.246.128.54955 > 192.168.246.13.80: S ...
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1answer
118 views

A LOT of connections from my external IP address to my web server

I installed Nagios recently on a Debian machine running an Apache web server among other things. The thing is that lately, Nagios tells me that the HTTP service is failing intermittently and it seems ...
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2answers
2k views

Recommended TCP keepalive settings for a busy server

We are having some network timeout issues on a Debian server that is quite busy, and maintains multiple connections to a number of other servers on the network. Here are our current TCP keepalive ...
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204 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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4answers
5k views

Is there a way to see what is actually filtering TCP port communication?

nmap -p 7000-7020 10.1.1.1 Will output all the filtered ports Starting Nmap 6.40 ( http://nmap.org ) at 2015-03-04 12:18 EET Nmap scan report for 10.1.1.1 Host is up (0.00091s latency). PORT ...
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4answers
4k views

apache webserver unresponsive with server-status showing all child processes waiting for connection

My setup: i have 3 nearly identical webserver machines serving the same high loaded dynamic website with simple load balancing over dns. The service has been working for over two years with the same ...
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1answer
280 views

How do I open specific ports on Linux (an AWS instance of RHEL v. 7)?

I'm using RedHat version 7. My AWS instances are in a security group with ample permissions for inbound connectivity. I can do Yum updates. The servers can ping each other. I can transfer files ...
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3answers
864 views

tcp-upstream in unbound doesn't work. Use TCP for query upstream DNS servers really work in the real world?

Today I've been playing with some options in unbound.conf just for fun. I've enabled tcp-upstream but it doesn't work with some domains. OS: OpenBSD current. Unbound: 1.4.19 Examples with ...
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3answers
3k views

HTTP not finishing over LAN. Hardware cause?

On a customer server running Apache 2.2 on Windows server 2012 we're noticing that from time to time, some requests to the server never finish. Using wireshark I've found a bunch of duplicate ACKs get ...
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90 views

TCP forwarding IIS

i have a server, let's call it: GATEWAY-SERVER (GS). On GS i installed a custom build TCP proxy/forwarder. This tool accepts connection TCP level and formulates a new request towards a TARGETSERVER ...
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1answer
74 views

SNORT only alerting on inbound traffic

I am trying to raise an alert when someone is setting up a connection to PORT 25 (tcp), whatever source or destination. For this i came up with this simple rule: alert tcp any any -> any 25 ...
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1answer
35 views

Windows Server 2008 sending regular TCP DNS requests to Forwarders

Our organization's primary DNS server is a Windows Server 2008 which two Forwarders set. I happened to notice on our firewall that this server is sending out regular TCP requests to the Forwarders in ...
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1answer
756 views

How to debug why WAN TCP/IP throughput is lower than expected?

I'm trying to figure out why tcp/ip throughput between two hosts I control is much lower than expected. Host A: internet connectivity provided by Comcast (Residential) in Boston Metro -- can ...
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1answer
418 views

(Why) does FreeBSD 'net.inet.tcp.always_keepalive' violate RFC1122?

While working on a server application that runs on FreeBSD and uses TCP, I noticed that TCP keepalive probes get sent even though my application explicitly disables SO_KEEPALIVE on TCP sockets. ...
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2answers
12k views

All connections from this network get stuck in SYN_RECV state, connections from my home or phone properly get ESTABLISHED

My server (a linode VPS) suddenly started to timeout on every request yesterday. I'm pretty inexperienced in networking and would love to learn a process for debugging these connectivity issues. ...
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1answer
11k views

Windows 7 default TCP connect timeout

Is there a way to change default TCP/IP new connection timeout ? In earlier Windows, timout value was stored in registry, as said here: Which is the default TCP connect timeout in Windows? But this ...
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4answers
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Which is the default TCP connect timeout in Windows?

Which is the default TCP connect timeout in Windows? There is a registry key to configure it or it's set dynamically?
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3answers
303 views

Send TCP/IP packets down three routes and pick fastest

Does there exist a way to split TCP/IP traffic across three routes and have the first packets to reach the destination be used? I'm imagining something like multi-homing but with the requirement that ...
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1answer
129 views

length of Tcp segment exceed MSS

I find a weird behavior in my Linux system, when I curling a web page, the received TCP segments are significant larger THAN the MSS. here is the output of tcpdump: 00:00:00.000000 IP ...
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2answers
68 views

Get a website's host machine's OS/server software without access to the server

Is there a good methodology to find the operating system and server software that is being used on a served website that you don't have SSH access to? What I'm doing right now is looking at TCP/IP ...
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100 views

Multipath tcp application level performance measurement

I am working on a project related to Multipath tcp and I want to measure the goodput and the RTT at the application level. I don't want to use a traditional tool(netperf, iperf, ...) and I want to ...
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0answers
762 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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6answers
1k views

Effect of distance from server on page load speed

I measured the load speed of a static image file severed by nginx from my server (using pingdom service). The server should normally process this request within few seconds. My server is located in ...
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564 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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298 views

Cisco ASA firewall blocking requests to internally hosted DNS server

I have a DNS server behind a Cisco ASA firewall. The Cisco firewall is performing NAT. When inside the network, I can NSLOOKUP directly to the server. When the client is external, requests time out. ...
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1answer
128 views

How to redirect all incoming packets to sniffer in Linux using iptables?

I need to redirect all incoming tcp packets from eth0 to current host (change ip address from 1.1.1.1 to 1.1.1.2) and outgoing tcp packets from sniffer from eth1 to another host(from 2.2.2.2 to ...
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1answer
243 views

server is not responding on SYN packets

On the attached tcp dump, the first two SYN packets (#21800 and 21801) came to the server, however SYN ACK was sent for the second SYN. Is that correct behaviour? My understanding is that the client ...
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3answers
197 views

how to use tcpdump to log only certain data in real time

I'd like to monitor network interfaces but only log things likes errors, collisions and dropped packets. The send that to stdout. – Can tcpdump be configured to do this?
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2answers
382 views

Checkpoint FW1 logging

When I view the logs created for my checkpoint fw1, does it log connections on receiving the syn, or does it wait till the three way handshake completes? If it logs after the syn, is there anyway of ...
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3answers
20k views

What's the difference between Unix socket and TCP/IP socket?

It's from this answer: http://stackoverflow.com/questions/2482411/is-this-pdo-bug-fixed-now/2482424#2482424
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1answer
4k 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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1answer
770 views

Unix socket connection limit

This may appear like an already discussed/answered question. But I am specifically looking for info which I couldn't find anywhere answered clearly. I have an Nginx + php-fpm setup which uses unix ...
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95 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 ...