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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Measure goodput before sending a response

My idea is to make it possible for web applications working on slower connections to fallback on alternative smaller asset versions(like images, videos, etc.). HTTP Live Streaming has similar behavior ...
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26 views

PLC actively refusing connection

I have a problem building a TCP connection between a PC a PLC. In short words: The PLC is waiting for connection attempts of the PC. The PLC has a static IP and two Ports (3011 and 3021) I can ...
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1answer
51 views

TCP connection; ACK not received

I am having trouble sending mail from Linux to Exchange server. When I telnet from Linux to Windows on port 25, I am not receiving any message from Exchange. The connection is automatically terminated ...
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11 views

Kamailio CPU usage very high and not accepting new registrations

I am facing a very strange issue with Kamailio, our Azure VM is D2 configuration with 2 cores and 7 GB of RAM, Ubuntu 14.04 LTS, through-out the day we see high CPU usage from Kamailio, and ...
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Troubleshooting for TCP exchange between an embedded Linux dist (OpenWRT) and a Fedora dist on a computer

I am facing an issue I did not succeed to solve. I have a device (Arduino Yun) using the OpenWRT distribution, on which I run a nodeJS machine to execute some function, and especially to send tcp ...
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1answer
23 views

rsyslog server listen only on tcp 514

I'm trying to set rsyslog client- server to listen to tcp messages with port other then 514, however it doesn't work. Only when using 514 it receives messages. I'm using EC2 vms. input(type="imtcp" ...
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1answer
588 views

Under HTTP2, how often are new TCP connections initiated?

I understand that HTTP2 aims to keep everything under a single TCP connection, and I was wondering how often TCP connections would be torn down. For example, if I visit youtube, do some browsing, ...
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10 views

ss vs iftop. send XMbps doesn't match

I'm troubleshooting a cross data center network issue, and I found this mismatched. In most case, the data is send from A to B, the port on B is 38790. @Host A [root@**** zhifan]# watch "ss -ati ...
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11 views

TCP ACK delay by app / windows on VirtualBox Windows VM

I have a .NET windows service that uses an open source library (Asterisk.net - C#) to listen to TCP connections on a specific port. This service is deployed on a number of VM instances of Windows 7 ...
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1answer
43 views

Server send TCP ACK with wrong number after receiving SYN

I have a client establish new TCP connection then sends request to a server per second. Both client and server are on the same linux box (via loopback interface). The client periodically reports ...
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17 views

Why my firewall rules aren't working in my NanoStation m2?

I have two NanoStation m2 as AP and Repeater for a wireless network (make them device1 and device2), both working in BRIDGE mode. Both devices are connected as WDS pairs to each other because they ...
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1answer
20 views

kill tcp port binding by deleting proc/[0-9]/net/… in linux

I have a script to call syscall Kill the process that holds a certain TCP port in Linux (ubuntu). But even if I do that, sometimes the port still remains in /proc/[0-9]/net directory binding the port. ...
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1answer
57 views

RST ACK with Reset cause

We have a device that connects over Wired LAN (Ethernet) to our cloud servers. At certain customer locations, when the device tries to send data, we are getting RST ACK from the customer server to ...
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1answer
79 views

What are the ports needed for L2TP VPN on Mac OS X Server 5.0.15?

I'm configuring a Mac as a server with a VPN service. So, I opened the ports listed as used by VPN in Apple documentation: UDP 500 -> 500 (+ESP and AH) UDP 4500 -> 4500 Any UDP -> 1701 (I got to ...
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2answers
745 views

TCP Messages Merged?

I have an application that sends 100 of 186-byte (excluding headers) TCP messages back to back without gap from host A to host B. I ran tcpdump to capture the packets on host A (where the sender is), ...
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31 views

Determine which equipment is causing packet loss

I'm connecting from my office to two servers (server 'A' and server 'B') hosted by two different providers. Since a few days, my connection speed to server 'A' has dramaticaly slowed down. Even when ...
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1answer
46 views

Linux: How to configure TCP wrappers in /etc/hosts.allow for manually started processes?

An internal server in the company I work for has been compromised and I would like to harden CentOS machines in the organization in order to avoid any future incidents so I've been reading about ...
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25 views

nginx monitoring failed to load status page under load

Nginx monitoring script so-called ztc failing to load nginx test page (mostly under highest load to nginx about 2000 rps, which used as proxy), causing errors like "nginx is down" on zabbix, and, in a ...
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15 views

socat Resource temporarily unavailable

I am using socat as a bridge between some devices and running socat (a couple hundreds of instances) like this: socat -d -d -d -x -d -lf "/var/log/some_log_file" ...
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24 views

How does TCP PSH and HTTPS works?

Right now I monitor traffic on my VPN server. I'm using tcpdump for it and it works pretty good. sudo tcpdump -n host SENDER_IP In this example you can see one HTTPS request from SENDER_IP to ...
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0answers
112 views

Why would Windows Server 2012 not respond on ports above 6000?

This is a new question but similar to this previous one. I've inherited the management of a Windows 2012 Server (not R2) and I'm unable to get a response from any ports above 6000. I have services ...
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0answers
36 views

Server socket sitting in FIN_WAIT_1 whilst network doesn't see its traffic

We've been trying to get a grip on a really weird problem where we can wget a page from Apache 2.2.19 on solaris 10 and some permutations of requests reliably take various fixed lengths of time to ...
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32 views

TCP buffer sizes and ethernet bonding

(This question was originally posted on stack overflow; Andy told me that I could get faster help here, so it is re-posted here now.) I am experimenting with TCP buffer size tuning on Linux, but ...
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0answers
74 views

How to change tcp's window size?

I've tried changing the tcp's window size by modifying net.ipv4.tcp_wmem and net.ipv4.tcp_rmem values, however the changes which I make have no effect on actual window size which I can check using a ...
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1answer
32 views

Why does data sit in Send-Q? TCP sessions freezing

Issue I run an IRC server for 20-50 users. We sometimes have issues with messages not arriving in a timely fashion or at all. After some packet captures we determined that messages sit in the ...
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1answer
30 views

Reduce TCP send buffer

I have a windows 2008 R2 server, an app is constantly polling another server (using a Flash Socket) while waiting for a certain event to occur on that server. We are talking about milliseconds. When ...
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29 views

Too Many TIME_WAIT Connections [duplicate]

We have issue that our application sometime can not connect to DB server which is a separate server. The application server and DB server communicate locally. So I search and found out that we have ...
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2answers
50 views

Does UDP includes of source address?

Both UDP and TCP does not include source address, but how does it say UDP IP spoofing is easier than TCP? For example, the following webpage also says about UDP vulnerability. "Unlike TCP, UDP does ...
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52 views

TCP RST/ACK packets not being sent back to NAT client with Forefront TMG

With Forefront TMG, we have an issue where all TCP connections to allowed ports work just fine when the connection is accepted with SYN/ACK, but when they are rejected with RST/ACK, the response does ...
4
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1answer
516 views

Why are connections in FIN_WAIT2 state not closed by the Linux kernel?

I have an issue in a long-lived process called kube-proxy being part of Kubernetes. The problem is that from time to time a connection is left in FIN_WAIT2 state. $ sudo netstat -tpn | grep ...
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1answer
59 views

TCP connection not established: Can't Connect to MySQL Server on Remote Connection (10060)

I'm running MySQL 5.6 on a WinServer 2012 system. It works great. The server is on our office intranet, not accessible to the outside world. I normally administer MySQL remotely from my office on my ...
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12 views

Iperf Tcp Client and Server

I'd really like to know why the bandwith in the client is higher than the server, i can´t find the answer explaining why this happens. Thank you, Tiago Melancia Values of the bandwidth: Client ...
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2answers
42 views

A small puzzle about routing

This is a followup to this question I saw on SuperUser, to which no answer has been provided. A user deleted the second route in his routing table, # ip route show default via 192.168.73.1 dev ...
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40 views

Configure a websocket server in front of HAProxy

I have a small python server script which creates a websocket connection and accepts base64 encoded IP packets (very similar to this). As of now my script decodes the IP packet and sends it out into ...
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1answer
90 views

Access to Proxy Protocol address within HAProxy

I am running HAProxy that is receiving layer 4 proxy protocol from an upstream source. I have a need to create a custom HTTP header with the address contained there. I can't seem to find how I can ...
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1answer
58 views

How to select different backend based on URI when using “mode tcp”

I am using haproxy version 1.6.2 I have enabled http2 using the config below which I need to use "mode tcp". But once I have switched from "mode http" to "mode tcp" I couldn't use acl path_beg to ...
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22 views

Not getting TCP Update Window packet after TCP Zero Window begins

Once I get TCP Zero Window during data transmission, I can't send data anymore in that desktop sharing session. Even I stopped the data sending to check if it can resume but no benefit! In my test ...
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78 views

Windows Telnet Could Not Open Connection On Any Port, Connect Failed

Configuration: Host: Hyper-V Windows 2008 R2 Guest: Windows 2008 R2 No firewall, no antivirus Problem: After 5 or 6 days, the guest cannot make any TCP connection to outside, neither can do to ...
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2answers
123 views

TCP timeout for established connections in Windows

I have the following situation: Application (Firebird DB client) on a client computer opens a TCP connection to server on port 3050 Application crash on client, application terminated netstat on the ...
2
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1answer
54 views

Permissions to ports Alfresco

When I restart Alfresco, it starts... I got the page... But on the logs I got the error: 2015-11-10 09:58:55,282 INFO [management.subsystems.ChildApplicationContextFactory] [localhost-startStop-1] ...
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1answer
104 views

Difference between net.core.rmem_max and net.ipv4.tcp_rmem

What's the difference between net.core.rmem_max and the third value of net.ipv4.tcp_rmem? Which has the higher priority for tcp connections? For below two examples, what's the max buffer for tcp ...
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1answer
92 views

Wireshark shows “TCP Dup Ack” on SACK after each regular ACK

I have a TCP session captured via switch port mirroring and tcpdump. When viewing it (in Wireshark), I see the same pattern whenever I send a message; here's an excerpt of the outbound packets (I ...
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35 views

TCP and UDP ports usually blocked [closed]

Which are TCP and UDP ports most likely to be blocked? I refer especially to the client edge of the network. To start I guess SMTP (25), SIP (5060) for TCP, Traceroute (33434) for UDP.
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1answer
74 views

Server sends ACK in response to SYN causing a reset in TCP request from the client

We are getting 7% reset messages for our TCP layer messages. We have two sets of logs. The first of Wireshark logs shows a good request and response Here the client was replied with sync ...
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1answer
62 views

tcp retransmit via curl and netcat

I'm trying to setup iptables to cause realistic network failures between docker containers. On the server, I run both netcat -lk 1234 and an Erlang cowboy server. On the client I run clients: echo ...
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2answers
56 views

Run ncat in background

from some time I'm trying to resolve very annoying issue: I need to have simple server which will listen on particular TCP port and throw all information which it recieve to trash. I'm doing it by ...
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1answer
48 views

Why is Apache2 serving as an iperf server?

My Question: Does anybody know why an apache2 server can act as an iperf server? I thought that an apache2 server does only answer HTTP requests. My Situation: I accidentally realized that an apache2 ...
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4answers
1k views

Netcat fails to start in listening mode

I'm using CentOS 6.7 (Final) system, and when I try to run nc in listening mode it prints the following: # nc -l 1234 nc: Protocol not available The port is not bound. I tried other port numbers ...
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39 views

Can iptables log all type of tcp connection?

Can iptables log tcp Split-Handshake and Simultaneous-Open connections as well as tcp Three Way Handshake? Here is these two kind of tcp connection descriptions. Here I find how to log new tcp ...
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88 views

Apache timeouts and TCP retransmission

The documentation for the timeout directive in apache states that: When writing data to the client, the length of time to wait for an acknowledgement of a packet if the send buffer is full. But ...