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.

learn more… | top users | synonyms

3
votes
0answers
236 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 ...
5
votes
1answer
138 views

POST of MTU + ~798 bytes gets lost

I have a very weird issue with certain packets not arriving on the destination host. It happens when we transmit a POST that is somewhat larger than the MTU. We can reproduce it with this script: ...
0
votes
0answers
79 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 ...
1
vote
1answer
908 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 ...
0
votes
1answer
50 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 ...
0
votes
1answer
55 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 ...
0
votes
0answers
27 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 ...
0
votes
0answers
32 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 ...
2
votes
1answer
80 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 ...
20
votes
6answers
18k 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 ...
1
vote
1answer
51 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 ...
0
votes
0answers
46 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 ...
7
votes
2answers
380 views

How does Intel AMT (Active Management Technology) not interfere with the TCP/IP host stack?

The Intel dev kit I've been using includes a remote management feature (also see the Ubuntu man page here) which allows remote reboots in case the operating system hangs. It has the capability of ...
1
vote
1answer
56 views

Hitting Ephemeral TCP Port Exhaustion

We run a high traffic website. Over the past few days, we've had several customers complain of sporadic downtime that we cannot reproduce. We have several web servers elected to receive traffic from ...
2
votes
4answers
7k views

How do I “Close Connection” like TCPView does, using the command line? [closed]

I'd like to do what TCPView does from the command line, for example, closing a connection used by a particular process (without ending the process). Is there a way to do this?
1
vote
1answer
987 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 ...
0
votes
0answers
29 views

Ghost tcp connections: ss sees them, nothing else does

We have a strange problem. Our remote server shows over 900 connections coming from our office over port 80: # ss -n | grep ESTAB | grep $OFFICEIP | grep :80 | wc -l 935 Netstat shows a similar ...
0
votes
1answer
78 views

Strange entry in open file list on Ubuntu server

On my Ubuntu server I occasionally run the following command to view any open files that are TCP connections from my server: lsof -uroot | grep 104.236.XX.XXX The last time I ran it, I saw this as ...
1
vote
1answer
52 views

No SYN/ACK answer from server

At first I describe my LAN organization. I have 2 Networks (scheme http://take.ms/s3CSy): 192.168.0.0 / 255.255.255.0, router ASUS RT-N65U with internal IP 192.168.0.1, static external IP without ...
0
votes
1answer
20 views

What does the tcp_fastretrans_alert error mean?

I found this error a couple of times in /var/log/messages after experiencing some odd TCP behavior: For some reason, if I connect to for example SSH for the first time in say an hour, the connection ...
0
votes
0answers
118 views

How many concurrent TCP connections are supported in Windows Server OSs?

I am distributing software in the form of a Windows service that can be installed, and am currently trying to ascertain the specifications for supported operating systems. The service communicates ...
3
votes
3answers
3k views

Allow X Client Display through TCP on Lucid

On Karmic, to allow other PCs to open and X-Window on a station, one had to edit /etc/gdm.conf and change DisallowTCP to false. That file no longer exists on Lucid. I tried changing an entry in ...
0
votes
7answers
1k views

Is it possible to redirect/bounce TCP traffic to an external destination, based on rules?

I'm not even sure if this is possible... Also, please forgive my ignorance on the subject. What I'm looking for is for "something" that would allow me to redirect all TCP traffic arriving to host A ...
-1
votes
2answers
64 views

how to force linux to accept packet with loopback ip

i have an embedded system with an Ethernet interface that needs to accept external packets with IP of 127.x.x.xx. is there a way to force Linux to accept external packets with this loop back address ...
0
votes
0answers
49 views

Unable to connect to remote MySQL from VPS

I am trying to establish a remote MySQL connection from one VPS to another. I have tried and done everything, I have allowed the outgoing TCP port (3306) in csf.conf, I have used Iptable rules online ...
33
votes
11answers
26k views

What is the difference between UDP and TCP?

My router has two protocols (and a "both" option) that I can select when setting up port forwarding: UDP and TCP. What is the difference between these two protocols and when would you select one over ...
8
votes
4answers
257 views

Simulate slow connection between two ubuntu server machines

I want to simulate the following scenario: given that I have 4 ubuntu server machines A,B,C and D. I want to reduce the network bandwidth by 20% between machine A and machine C and 10% between A and ...
1
vote
2answers
40 views

Clients phone provider claiming high latency over UDP, how do I test?

A client of our uses a hosted phone solution for his 50 agent call centre. They use a hosted dialer who make the out going calls, once the connection is made the call is passed to my clients user ...
1
vote
0answers
55 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 ...
1
vote
0answers
114 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 ...
0
votes
2answers
70 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
votes
2answers
482 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: # ...
0
votes
1answer
50 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
vote
0answers
184 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 ...
0
votes
2answers
70 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 ...
0
votes
0answers
299 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
vote
2answers
251 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
vote
0answers
38 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) ...
-1
votes
1answer
83 views

Is ARP Connection oriented or connectionless?

Is ARP Connection oriented or connectionless? It uses TCP, but does that consider it connection oriented?
0
votes
1answer
33 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?
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
vote
1answer
95 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 ...
4
votes
1answer
130 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 ...
-2
votes
1answer
98 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 ...
16
votes
6answers
29k 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
vote
1answer
90 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
26 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
vote
1answer
721 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 ...
1
vote
4answers
227 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
31 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 ...