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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5
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3answers
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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 ...
1
vote
1answer
891 views

TCP Zero Window with no corresponding Window Update

I am trying to debug a network issue and am using Wireshark and tcpdump to grab packets from my server. I have one client application that is grabbing all my available connections and then holding ...
1
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0answers
84 views

trying to reach a port forwarded server from the subnet using the public IP not working

I set up a server which is connected to my router. The router forwards a port of my server. So when I scan that port using http://www.t1shopper.com/tools/port-scan/ I got: 188.143.126.14 is ...
2
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1answer
936 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
1answer
966 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 ...
0
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2answers
47 views

TCP - TAP performance

Linux. Is there a performance loss from using a tap device vs a hardware one like eth0 ? The goal is to create a user space tcp/ip stack and avoid the kernel as much as possible. I would like to be ...
0
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2answers
56 views

Implementing TCP Sticky Sessions With HAProxy to Handle SSL Pass-through Traffic

How can we implement session stickiness in HAProxy when SSL must terminate on the backend servers? We need the stickiness because backends cannot share sessions. This is my original configuration: # ...
3
votes
4answers
2k 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
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1answer
28 views

Proxy-attack simulation

I have a WS2008 x64 server, that has NodeJS application working on its 80 port. Server constantly receives queries from different IP-addresses that are trying to use my application as a proxy. NodeJS ...
1
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0answers
46 views

Cannot make TCP Connection with OpenVPN Server

Client OpenVPN assigned IP: 10.8.0.2 ↓ TCP on 1194 Internet ↓ Router port-forwards 1194 to server- Public IP 104.162.67.198 ↓ Server LAN IP: 10.8.0.1 I think the above is what I am trying ...
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0answers
32 views

Route 53 TCP Health Monitoring with NC

We have multiple servers which are running UBUNTU 12.04 OS. We would like to create health monitoring for all of the servers. Since none of the servers are running web server I would like to create ...
0
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2answers
31 views

Display IP & TCP statistics per interface (netstat -s with interface)

Linux has the ability to display protocol statistics with netstat -s. The output looks something like: Excerpt: 7487 times unabled to send RST due to no memory TCPDSACKIgnoredOld: 817 ...
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0answers
44 views

WSAECONNREFUSED SAP Gui unable to connect on SAP server on hp ux - inetd.conf file reference

I have a sap server installed on HP-UX vm, up and running. when I try to connect to the server from SAP client GUI installed on windows machine I get the following error --------------------------- ...
1
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2answers
236 views

How is a TCP request routed from a virtual machine to an outside resource and back again?

Scenario: Computer A has a local ip of 192.168.1.100, which is running a VM inside of it. The VM now makes a tcp request to an external IP address (74.125.225.98). Could someone explain how the ...
1
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0answers
17 views

delay in ACK packets for ldap abandon request

we have migrated from an openldap server on linux to a DirX on windows 2008. The ldap server und normal serch request behaves as expected. However with some applications (weblogic deployed webapps) ...
0
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1answer
61 views

Is ARP Connection oriented or connectionless?

Is ARP Connection oriented or connectionless? It uses TCP, but does that consider it connection oriented?
0
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1answer
31 views

What is the maximum number of characters in a service name?

In TCP/IP, a service name (like http or smtp) is an alias name for the port number. What is the maximum number of characters that can be used in a service name?
0
votes
2answers
1k views

How do I get my ubuntu server to listen for database connections?

I am having a problems connecting to my database outside of phpmyadmin. Im pretty sure this is because my server isn't listening on port 3306. When I type: sudo netstat -ntlp on my OTHER working ...
3
votes
1answer
2k views

Block all incoming DNS requests EXCEPT from IPs x,y,

I want to block all incoming requests on my two DNS servers APART FROM certain IP addresses e.g. IP of 1.2.3.4 will be allowed to make requests but NOBODY else will. How do you do this with iptables? ...
1
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1answer
76 views

Limit Number of TCP connections in Linux Server, to avoid attack

I want to limit the number of TCP connections in Linux server, I have used the following command. iptables -A INPUT -p tcp --syn --dport 80 -m connlimit --connlimit-above 25 --connlimit-mask 32 ...
0
votes
1answer
2k 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 ...
1
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2answers
813 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 ...
4
votes
1answer
117 views

Change TCP wait for ACK timeouts in Win7/WinServer

Is there any possibility to change default wait for ACK timeout in TCP network on Windows 7 or Windows Server ? I'm using very slow network ( 1200 bps ) and want to tweak TCP. When using default ...
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votes
1answer
52 views

What is the best way to measure latency via a “telnet to port” test, preferably with built-in Linux tools?

I'm writing a Graphite/Diamond collector measuring network latency. Specifically it should measure the time it takes to open up a connection to a port on a remote server. And it needs to work via ...
15
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6answers
26k views

How to capture ack or syn packets by Tcpdump?

I want to use a filter rule to capture only ack or syn packets. How do I do this?
1
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1answer
49 views

Tuning Linux TCP for large number of TIME_WAIT

It looks like we have a bunch of tcp connections hanging around on a busy webserver, this is the output from ss -s: Total: 366 (kernel 1037) TCP: 72108 (estab 130, closed 71964, orphaned 0, synrecv ...
0
votes
0answers
15 views

windows firewall , some ports not listening

I've added an inbound connection rule for my windows 8 firewall on windows server 2012: I've restarted the Windows Firewall. When I check that port using this program, it says that it is not ...
1
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1answer
584 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 ...
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4answers
207 views

Is there a netstat -s equivalent for windows?

I know that netstat -s exists on Windows, but it displays way less informations than on Linux/OS X. It only gives 8 counters about TCP, while on Linux it's more than 50. I'm looking for any ...
0
votes
1answer
16 views

Solaris 11 / OpenSolaris - stop processes from listening?

I would like to write a script to secure Solaris 11 servers in preparation for internet access. In addition to enabling ipfilter, I would like to disable network-accessible services that are not ...
0
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0answers
19 views

Dropped TCP Packets over two-stage IKEv2 VPNs

Something of a weird setup this: There are two Virtual Private Clouds (10.100.240.0/20 = prod1 and 10.101.0.0/24 = control), which have a valid router between them. Control hosts a VPN that is meant ...
5
votes
1answer
1k views

Finding short-lived TCP connections owner process

Running tcpdump on local connections to an apache server, I found TCP connections being established and closed immediately every 2 seconds. How do I find which process is responsible for these? ...
3
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3answers
3k views

Easy way to “edit” the traffic coming from a tcp host (linux)

I need to make some small modification to incoming traffic from a known tcp host:port before the process handling the connection get the stream. For example, let 192.168.1.88 be a remote host which ...
0
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1answer
66 views

NTttcp shows slower throughput on loopback (127.0.0.1) than on network

I am using NTttcp to find a baseline for what throughput I can expect between a client and server on windows. When I ran the client and server on two different machines on our LAN I got the following ...
1
vote
5answers
69 views

Get number of TCP established connections

On a Linux server one can use netstat -tan | grep ESTABLISHED| wc -l but this will not work on a high load server with watch -n1. Such approach works fine if the server is not very busy or the ...
11
votes
13answers
21k views

How to discover the MAC address of machines in a network?

How do I discover the MAC address of machines in a network? I need to discover the machines that are available just with only BIOS installed (no operating system). And I need to find the MAC address ...
0
votes
1answer
41 views

TCP Load balancing

I need to implement an architecture that can serve 3 million GPS Devices sending Location Updates/Alerts (every 10 secs) to our system for processing. Features: 1) TCP communication. 1) Long lived ...
3
votes
2answers
3k views

Netstat -s showing (and growing) “packets pruned from receive queue” and “packets collapsed in receive queue”

we are seeing the following: [root@primary data]# netstat -s | grep buffer ; sleep 10 ; netstat -s | grep buffer 20560 packets pruned from receive queue because of socket buffer overrun ...
6
votes
2answers
822 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 ...
0
votes
1answer
60 views

How does an IP address goes down from an Application Layer to IP Layer? [closed]

Using the classical TCP/IP layers model, I am thinking about an application (for example a browser) acting as a client wanting to talk with a server (e.g. a web server). Of course it has to use the ...
2
votes
1answer
93 views

TCP piggybacking introduced by a man-in-the-middle network node beween the client and server?

When wireshark trace taken on the client side it appears to be: ---SYN---> <-SYN-ACK- ---ACK---> -HTTPGET-> But when wireshark trace taken for the same traffic on the server side it ...
7
votes
2answers
825 views

Varnish running out of open ports, lots of SYN_SENT connections

Recently we've been experiencing issues with our Varnish (3x) -> Apache (3x) setup, resulting in a huge spike in SYN_SENT connections. The spike itself is due to the amount of new traffic hitting the ...
3
votes
0answers
88 views

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 ...
2
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0answers
52 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 ...
0
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2answers
90 views

Proxying TCP by hostname

I've got multiple game servers TCP ports on my single host machine. The goal is to have users be able to connect to server1.domain.net and have their directed based on that subdomain. My first ...
0
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0answers
55 views

TCP ignores some packets for no reason

I have a weird problem which I can't understand. The actual network configuration is quite complex, because I am using Openstack and Docker to build a virtual network. However, the problem is not ...
3
votes
0answers
107 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 ...
32
votes
1answer
904 views

Random TCP RST's on certain websites, what's going on?

Short version: One Windows Server 2012 machine on my network is getting persistent but intermittent TCP RSTs when connecting to certain websites. Dunno where they're coming from. Check out the ...
0
votes
2answers
104 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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votes
2answers
54 views

TCP/UDP Small Package Size optimization [closed]

I currently have the problem, that when a LOT of RTP streams (>800) go to one server the max. speed is onlynabout 70-80 Mbit (on a Gigabit LAN - all Hardware components are Gigabit components) 130 ...