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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Tracking down failed TCP connections [on hold]

Windows performans log full with "More than 10 tcp connection failures per hour" message. Any idea how to track down what cause this? (I think its not normal!?) Thank you
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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
19 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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56 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. ...
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Azure intermittent outbound connection failure to EC2 [on hold]

I have three Linux VMs (Ubuntu 14.04) running in a vnet, like this: Host Internal IP External IP prod1 10.0.1.1 104.45.234.56 <---\__ load balanced prod2 ...
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27 views

Forwarding ports and traffic to VPN tunnel

I've installed OpenVPN on my VPS. I have one question: how to forward traffic going to that VPS to go to VPN tunnel created with my local PC. I will use TCP connection. The whole traffic will be like ...
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30 views

Routing traffic from VPS to private IP [closed]

I have ordered VPS on Digitalocean. I need to route all incoming traffic from this VPS to my local PC, which dont have public IP. I have read about reverse proxy and about VPN. Is it possible to route ...
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3answers
167 views

How can one redirect to a new host all traffic destined for an old host?

We're moving a bunch of services, say from 1.2.3.4 to 5.6.7.8. In order to test that the new services are correctly configured, we'd like to redirect (to the new host) all traffic destined for the ...
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19 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
55 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
27 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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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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2answers
121 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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2answers
43 views

is it normal for NGINX to accumulate connections in writing state?

This is a graph showing connection count from nginx's stab_status, the drops in graph are server restarts done manually. I find this behaviour strange, looks like some leakage. I think there are ...
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1answer
26 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
21 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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37 views

TCP connections drop off after initial build up

A bizarre problem on a production setup. Scenario 1) A server listens on a particular port. 2) There are potentially thousands of TCP connection requests. 3) About 200-300 TCP connections reach ...
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1answer
35 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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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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1answer
51 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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0answers
23 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
1k 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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1answer
42 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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19 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
49 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
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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
127 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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1answer
21 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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113 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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64 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
45 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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1answer
36 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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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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3answers
59 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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PCI says port 36141:TCP is blocked. But 36141:TCP open on iptables

PCI compliant scan fails due to port 36141:TCP is being blocked on website. I verified I cannot connection via 36141 on same server to itself: # nc -zv 127.0.0.1 36141 nc: connect to 127.0.0.1 port ...
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37 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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1answer
87 views

Concurrent TCP connections on Azure can be upto 500K. Really?

Let me be very clear at the outset that I am new to cloud technology. All I know is cloud servers are easily scalable (i.e. adding physical hardware is transparent to applications and users) and ...
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1answer
92 views

Linux clients can't connect, server and TCP Windows Size / Timestamps issue

We have a problem that a number of clients (all linux Ubuntu) are sometimes not able to connect to a remote server over SSH. If the problem occurs, Windows clients don't have that problem and can ...
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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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112 views

NetTcpPortSharing process won't start on Windows Server 2012 R2

I have a problem in Windows Server 2012 R2 : I have searched and try everything I know to fix this, but I cannot start NetTcpPortSharing service and therefore I cannot configure Windows Server ...
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137 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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1answer
67 views

TCP: out of memory - Nginx

I'm running a high traffic site on a nginx server. Last fews days I'm having problems with my VPS locking up (unable to SSH, and nginx seems to be down). When I look in the logs I can see the ...
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1answer
69 views

TCP packet loss against SQL-server

Where I work, we have had some issues with connections to the database. We get a lot of failures which appear as "recv failed" on the client side. I have used Wireshark to try to debug the problem and ...
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54 views

Reverse proxy encrypted java traffic on non-standard TCP ports on Windows Server 2012 R2

I'm trying to find a software that will run on Windows Server 2012 R2 that can reverse proxy TCP traffic without caring about the layer 5-7 details. By reverse proxy, I mean the software needs to ...
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37 views

RHEL6.4 server did not send a SYN/ACK packet in response to a SYN packet from AppDirector intermittent

In my case, client access this RHEL6.4 server thought AppDirector, so the TCP connection is from AppDirector to the server. According to wireshark, sometimes, RHEL server didn't respond for the first ...
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1answer
66 views

PHP-FPM TCP connections not terminating in time

I'm serving Wordpress pages via nginx/PHP5-FPM using APC caching (through the W3 Total Cache plugin). Nginx communicates with PHP-FPM via TCP sockets on port 9000. I've adjusted the number of max ...
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47 views

Bad ping results while testing 6000 TCP clients with 18 mbytes/s total traffic on Windows Web Server 2008

The clients are running on the machine #1. The server is installed on the machine #2. The machines have a gigabit connection through a switch on their private vlan. There are no errors in the switch ...
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1answer
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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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2answers
52 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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1answer
106 views

TCP Upload Speeds Slow to the Internet over LFN

I've got two Linux VMs separated by a 50 mbps WAN connection. There is about 70ms of RTT on this WAN link, so it's got some latency. I've been testing my upload throughput to the Internet from each of ...