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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Why does my firefox send TCP packets even when idle? [migrated]

I run firefox on Debian. I've disabled all mumboo-jumboo healthy and crash report tracking. There is no TCP connection to any website, I leave firefox oppen at the 'create new tab' When I turn off ...
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22 views

Monitoring IBM AS400 TCP/IP Traffic

Server Fault! I have been looking at some current IT jobs in my area and notice that a lot of the factories have openings for those with AS400 skills. I have applied for one that states that AS400 ...
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1answer
42 views

Tcp connection breaking, too fast for serial?

I've been having real difficulties getting a tcp connection to work with my web server. I think the issue might have something to do with the speed or ordering of the packets as the connection seems ...
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4 views

Connection interruptions on Debian router, possibly due to excessive duplicate ACKs? [migrated]

I have a Debian server as a house router, which for a year has been working flawlessly. However, I recently moved and switched service providers from FiOS to Comcast, and possibly as a result am ...
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28 views

Why would Windows 7 not complete this TCP handshake?

One of our customers is running Windows 7, and cannot reach some of our servers because it seems Windows 7 cannot complete a TCP handshake. Here's a packet trace to one our servers -- note that a SYN ...
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17 views

Spurious retransmission, Dup ACK and HTTP 408

I have a server which serves as sms gateway (using kannel) and have multiple client connecting to it, but recently this one client with their particular IP said that they can't send to my server and ...
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31 views

How to prevent TCP retransmissions? [closed]

I am using cURL to grab some data from websites. Some times (one out of ten) I get a time-out error from cURL but I am sure that the site is running (I can open it). In Wireshark I see TCP ...
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20 views

Citrix NetScaler sending FIN, ACK for SSL VPN Clients

I realise that it's unlikely anyone here has a definite "Check this box to resolve this" answer, but I'm struggling with this issue and I'm hoping that someone with more knowledge than me can give me ...
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1answer
20 views

TCP Keepalive: Why does an idled ESTABLISHED connection end after 60 seconds, instead of tcp_keepalive_time?

I am investigating ways to mitigate a server against DoS-type attacks. In one scenario, I've opened several hundred TCP connections to my webserver. I do not send any data after the initial TCP ...
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0answers
12 views

Route only on output chain?

I have two machines A and B. I want to send iperf traffic from A to B, but first have it route through a userspace program on A. I did this with a tunneling device: therefore, I used the command ip ...
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20 views

SYN/ACK not received by iperf client?

I have an application that essentially consists of four components A, B, C, D. A and B are on the same machine - B and C are separate machines. Traffic is generated by an iperf client on A with a ...
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3answers
562 views

TCP sequence number

I would like to know if two segments of same sequence number arrive at the destination, which segment will get accepted ? For eg: A clients sends a packet to a server and wait for an ...
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1answer
19 views

ufw status (what does the v6 stand for?)

My ufw status output looks like this: To Action From -- ------ ---- 22 ALLOW Anywhere 80/tcp ...
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29 views

Two processes stuck on network communication

We have had hang on our Oracle extraction process very intermittantly. Nothing obvious from the Oracle side, and starting to think it is more network related. There are two Oracle processes ...
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0answers
27 views

Debian limit number of TCP sockets for a process (especially tor) on OpenVZ

I have a debian 7.8 server, running on OpenVZ. On this server I'm running a tor relay and some other network services (like apache and mysql). However the tor service seems to eat up all my available ...
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0answers
19 views

Network sensor for a TCP connection for collecting statistics each second [closed]

I need a Network Sensor capable to gather basic end-to-end statistics (packet loss, jitter and network delay/RTT) of several TCP connections directed to the very same destination (ip-addr:port) on ...
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0answers
15 views

rsyslog tcp packets containing multiple log messages

I have rsyslog receiving logs over udp and then relaying them over tcp to a load balance (nginx) which passes them along to SIEM collectors. The setup looks like this: network devices/appliances ...
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0answers
9 views

delayed tcp fast retransmission

I operate some HLS servers based on Redhat Linux. I have a big problems. In streaming from HLS server to Client(smartphone), there are occurred some packet dropped. And then, Server received a lot of ...
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21 views

Should I disable the Nagle Algorithm for Outlook / Exchange RPC/HTTP communication?

I'm investigating reasons why several Outlook clients in non-cached mode are having delays communicating... resulting in Outlook hanging. My suspicion is that a Netscaler, or intermediate device (? ...
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1answer
28 views

Can TCP be used like UDP by simply not sending ACK?

Assuming both client & server cooperated, could you emulate the functionality of UDP by not sending ACK packets, and not sending retransmissions? Or would most routers somehow bork the process if ...
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31 views

SSH stalled after a while

I am executing some commands over SSH from a linux client (centos 7) toward a server (wind river linux) and for a reason it always stopped ( not completed ). If i executed a command that take short ...
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1answer
24 views

REDSOCKS goes 'out of file descriptors' when trying to redirect all outgoing (TCP) traffic from my Linux machine

I'm trying to redirect all outgoing TCP traffic from my linux box to the remote SOCKS5 proxy server. Currently I'm using the following rule in the OUTPUT chain: sudo iptables -t nat -A OUTPUT -p tcp ...
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0answers
33 views

Web sites freeze after clicking link - unexplainable ACK packet

We have a sporadic problem accessing some internal links on websites. (Windows Firefox, Internet Explorer, Chrome) Behaviour On first clicking a link, the browser will load infinitely. The second ...
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29 views

How to properly configure security group at AWS?

I'm trying to reach my server's FTP-port by its Elastic IP. I've configured the security group as follows: Inbound Type Protocol Port Range Destination All traffic All All ...
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1answer
58 views

Private communications between AWS EC2 instances

I have three EC2 instances with elastic IPs. Each one contains a server. Each server needs that TCP ports 8181, 2181, 2888 and 3888 are opened on each machine. Each server should have the possibility ...
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88 views

SynProxy can not return syn ack packets with asymmetric dual bridge topology

I have a asymmetric dual bridge topology as shown below when i connect from 172.16.11.5 and 172.16.10.6 with ssh but i can not connect because of SynProxy. ------- ...
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1answer
35 views

TCP - MSS option and different payload

This is a tcpdump from servers side. In line 1 i see MSS=1400. Why server sent in line 6 a packet of 4230 bytes when client want max 1400?
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How does server-side `TIME_WAIT` really work?

I know there are quite a few SE questions on this, and I believe I read as many of them as it matters before coming to this point. By "server-side TIME_WAIT" I mean the state of a server-side socket ...
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7answers
2k views

Why is it good practice to compare checksums when downloading a file?

Websites which supply ISO files for download will often give the md5 checksums of those files, which we can use to confirm that the file has downloaded correctly, and has not been corrupted. Why is ...
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2answers
254 views

Extreme UDP packet loss at 300Mbit (14%), but TCP > 800Mbit w/o retransmits

I have a linux box I use as the iperf3 client, testing 2 identically equipped Windows 2012 R2 server boxes with Broadcom BCM5721, 1Gb adapters (2 ports, but only 1 used for the test). All machines are ...
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1answer
52 views

Outgoing packet has NATed src address

Configuration/Topology: There are 3 machines hadoop2 | hadoop | driver eth0 10.10.15.3 | eth0 10.10.15.2 | tap0 192.168.0.199 ...
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1answer
49 views

No response to TCP SYN packet when padding is not 0's or F's

I have this client which initiates a 3 way handshake with a SYN packet but there is no SYN ACK response. We figured out that it was because the client did not pad the end of the TCP headers with 0's ...
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1answer
22 views

Upgrading Web Application's Systems' Kernels for IW10 & other related improvements - upgrade all machines? LB first? Most important?

Stackers - We're making the push to upgrade the systems for our web app to take advantage of the various TCP improvements becoming more readily available (e.g. ...
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112 views

Nginx TCP Fast Open Issue

I have configured Nginx and Apache on one of my servers. The nginx server listens on port 80 and Apache on port 81. Nginx works as a reverse proxy. In nginx I configured TCP Fast Open: server { ...
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40 views

What happens if a machine gets a SYN/ACK packet without sending initial SYN packet?

I'm thinking of a situation where an attacker manipulates a SYN packet that was sent from A's source IP address to B. The server will receive the packet and think it's a legitimate packet, and send a ...
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11 views

How to make TCPFlow to not store package body?

Is it possible to configure tcpflow to store only package headers without package body? My log simply explodes in production.
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58 views

haproxy get ssl interrupt error, how haproxy tell server to close ssl or tcp?

I use haproxy 1.5 and a windows server build site. my site work under the https protocol, so for haproxy I use tcp mode since I think the ssl can not work on http mode. my problem is the ssl ...
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0answers
27 views

Can I use a domain name for a TCP process hosted in IIS?

I'm trying to set up a WCF service hosted in IIS 7.5, with TCP bindings. I also need to use a SSL certificate for security. From what I have read, I can add net.tcp as a binding type. However when I ...
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1answer
34 views

ssh tunneling lmgrd port what I've missed?

I've got 2 machines: one local , one flexserver I'd like to do a ssh connection for forwarding the TCP port of the flexserver. On the flexserver, lmutil lmstat -c 5280@localhost is working fine So I ...
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1answer
53 views

How to ping a host with different MTU size to simulate icmpv6 packet too big scenario?

As the Title states,I want to check whether my host will actually send a ICMPv6 packet too big if i send a packet with beyond the defined MTU size.I don't have a cisco router(extended ping) to try out ...
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160 views

massive amount of CLOSE_WAIT due nginx (lsof)

My VPS keeps hanging up every 5 days. I can see that the nginx worker processes are eating up my memory over time. I think this is due the massive amount of CLOSE_WAIT's open. When I type LSOF, I get ...
6
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3answers
319 views

Why is my web server dropping connections with a TCP reset at high load?

I have a small VPS setup with nginx. I want to squeeze as much performance as possible out of it, so I've been experimenting with optimization and load testing. I'm using Blitz.io to do load testing ...
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1answer
217 views

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
42 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
166 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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0answers
88 views

Azure intermittent outbound connection failure to EC2 [closed]

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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1answer
77 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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3answers
283 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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0answers
58 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
72 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 ...