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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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
656 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 ...
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1answer
109 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
343 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
223 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 don'...
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51 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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166 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
137 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
86 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
65 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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5answers
3k 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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49 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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161 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 ...
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28 views

Why might a connection stay in TIME_WAIT for hours or even days?

Our environment is ubuntu 12.04 on EC2. I know TIME_WAIT is a good thing, and I know generally it's OK to see connections remain in TIME_WAIT for up to 2 minutes according to all the reading I've ...
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1answer
105 views

On-the-fly decoding HTTP bodies on Linux?

My wish is to monitor HTTP exchanges between my server and a browser. At present time, I use the localhost because I'm developping the app. I installed and used tcpflow and found it quite useful but ...
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39 views

Logging Simultaneous Open Connection Establishment With Iptables

Simultaneous Open Connection Establishment: TCP is also set up to handle the situation where both devices perform an active OPEN instead of one doing a passive OPEN. This may occur if two clients are ...
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2answers
54 views

Can a poor client VPN connection corrupt a database?

We have a small office with one server and one client that connects to the server’s database for the Sage 300 accounting software. The server is also being used as a workstation for the Sage 300 ...
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1answer
130 views

Ubuntu 14.04 TCP established hash table entries

A bit of background I am running two servers under high traffic one with ubuntu 12.04 (linux 3.2.0-69-generic) and one with ubuntu 14.04 (linux 3.13.0-52-generic). I am now trying to secure both. ...
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14 views

(Windows Media Encoder) TCP connection randomly fails/succeeds

We have a windows media server running and are pushing a stream using Windows Media Encoder 9 software on the client. Sometimes, it can't connect to the server and sometimes it can. I ran wireshark ...
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47 views

TCP Syn cookies is it always turned on when enabled?

For Linux kernel 2.6.32 if I set net.ipv4.tcp_syncookies = 1 will that be always used or only during a SYN flood attack? I found 2 sources which says the opposite. 1: "There are, however, two ...
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1answer
70 views

Stopping exploits based on Reversing TCP [closed]

One of the most common exploits on msf, reverse tcp by buffer overflow i guess is my concern. Can i, by any means stop of manage my tcp ports to deny giving access to rhosts and become safe from this ...
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3answers
306 views

Strange limit of 65536 max tcp incoming connections

I have a Linux server with an Erlang application which shows an odd limit of exactly 65536 max tcp incoming connections. The Erlang application is written with the Cowboy framework. I have tuned the ...
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1answer
257 views

tcp_tw_reuse and tcp_tw_recycle not working in specific environment

We are running HAProxy to direct mysql traffic from PHP to a set of mysql servers. However, due to an issue with the way the mysql-client sends TCP packets, we get a ton of connections in TIME_WAIT ...
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119 views

TCP Established connection spike in AWS

We are using AWS ELB in HTTP mode and are observing a spike in TCP established connection on Tomcat server. We have Apache HTTP server with mod_proxy between ELB and Tomcat. Apache and Tomcat run on ...
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109 views

Network speed between Windows 7 machines sharing over samba/SMB not reaching 10Gb/s

I have two Windows 7 Machines that are connected via 10Gb/s Intel Server Cards on a 10Gb/s Switch an a subnetwork(Physically separate from the larger main domain network). I'm trying to copy files ...
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1answer
135 views

random server timeout connections

I am searching for a solution for this issue for 2 days now. I have a centos server, and I get random timeout connections error, about 10-20% of the times. yesterday it happened to one of my users, ...
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114 views

TCP Out-of-order packets over GRE causing disconnect

I'm experiencing an issue with a small percentage of TCP connections over a GRE tunnel between two servers. The topology is basically Internet <-> GRE Tunnel <-> Backend The GRE tunnel and the ...
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1answer
274 views

Can I use HAProxy to load balance telnet connections?

We use HAProxy as load balancer for regular HTTP requests. I see no reference to telnet connections in the HAProxy configuration guide: HAProxy config guide. I was hoping to reuse HAProxy (or spin up ...
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89 views

Wireshark RST against TCP Zero Window

During application sharing with Microsoft Lync Client (Mac OS X), TCP ACK with RST flag is sent from my application end to Lync end against TCP Zero Window packets and call gets dropped. Image Link. ...
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2answers
56 views

SMB / CIFS / Samba Connectionless or Not whilst transfering files?

I have been researching this for a bit, but I have been getting conflicting answers, does samba, from my gatherings, SMB runs on ports TCP & UDP 137-139 & 445. But I have no idea therefore ...
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28 views

Is there an option that influences the RTO time in TCP?

I'm just trying to understand how retransmission feature works in the case of TCP on my linux box, but on the internet you can find really different information most of which is outdated or wrong, so ...
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1answer
163 views

slapd running fine and listening on port 389, but still can't contact

Here is my ldapsearch command with debug (I've masked my real IP address): $ sudo /usr/local/bin/ldapsearch -H ldap://99.99.99.99 -b dc=my-domain,dc=com -x -d -1 ldap_url_parse_ext(ldap://99.99.99.99)...
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147 views

how to get parameters of Linux module when it is compiled NOT as a module

when a part of Linux Kernel is compiled as a module on could read available parameters with modinfo and set them when loading with modprobe. Is it possible to get the values of paramters of ...
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2answers
51 views

What is the cause for TCP flow control misinterpretation?

The client cannot connect to our web server. I sniffed the client and web server only to found out that the client sees the TCP connection to be successful while the server see it as a failure. What ...
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352 views

Sometimes unable to tune Linux TCP stack for improved high-latency performance

I have been unsuccessfully trying to apply the TCP Tuning techniques discussed at http://fasterdata.es.net/host-tuning/ As you'll see when you read through the entire question, sometimes the es.net ...
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0answers
31 views

CentOS appliance becomes unresponsive with lot of outgoing http connections [closed]

I have an ESXi VM running CentOS-7. My application is deployed inside a tomcat instance running on this server. The application periodically makes 1200 "outgoing" http connections every 15secs. I am ...
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1answer
86 views

notify when a TCP port start listening

I need to be notified exactly when an application start LISTENING on any/specified TCP port. is there anything like configuring an application to log this event using a library in any programming ...
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0answers
91 views

Should I change the value of TcpTimedWaitDelay after increasing the MaxUserPort's value?

I have Apache running on Windows 2008 R2. I had an issue where my Windows Server is reaching maxing outbound TCP connection which caused many connections to be interrupted and my application started ...
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1answer
461 views

Server 2012 R2 TCP Timestamps

We will be having some penetration testing performed shortly and looking to clean up a few things. One of these is TCP timstamps in Windows. A simiple NMAP scan shows me a guess of the TCP timestamp ...
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1answer
42 views

Why is the same socket in TIME_WAIT many times?

I have read other threads regarding sockets in TIME_WAIT, but I am clearly still missing something. Below is a few lines from a "netstat -an". How could it get into this situation? If I understood ...
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1answer
38 views

Send proper UUID over tcp

I have a small ingest TCP server that should accept a device UUID as a first message, which is only 16 bytes. I'd like to test this manually from terminal, but sending a string won't work, since it ...
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1answer
75 views

Is “keeping alive connections” the smartest approach to access devices behind a router? [closed]

The problem I'm developing an IOT device that will connect to a common Wifi router. As you know in order to make this device publicly accessible from WAN you'll have to do some ports forwarding or ...
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140 views

tcp previous segment not captured when NAT

I have a client request web service on a server behide NAT. My client IP is 10.54.10.193 NAT address: 10.54.28.183 Server address: 62.209.39.203 When client request web service on server we have TCP ...
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2answers
225 views

Keeping TCP connections alive to track which clients are online

I am developing an application where a server needs to stay in touch with lots of simple IoT devices. Nearly no information exchange is needed between the server and each device, but devices need to ...
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0answers
152 views

Inconsistency in TCP and HTTP connection management

I observe following scenario in WireShark: The problem I see here is that after receiving [FIN, ACK] from server (4090) and acknowledging it (4092), http client attempts to send another HTTP ...
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1answer
95 views

Packets being routed to the wrong IP

Looked around, can't find a similar issue anywhere... I have been having some very strange and hard to explain problems on my network lately, and in my efforts to find the cause, I came across an ...
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77 views

What exactly constitutes a bad TCP segment?

What constitutes a bad segment as in bad segments received in the netstat output below? I would think a TCP header's checksum could do it, but are there other things? If a segment arrives after its ...
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1answer
152 views

(Completely) randomize IP addresses in PCAP file

I have several PCAP files which contain network traffic. To perform some experiments for a network experiment, I need real data with completely randomized IP addresses. I am well aware about the ...
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1answer
97 views

Configure Squid Proxy Server to use TCP for DNS lookups? [closed]

Is there a way to configure squid 3.5.1 to use TCP for DNS lookups? I've setup up the proxy server to use TCP for lookups by adding "options tcp" to my /etc/resolv.conf, but squid seems to be doing ...
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1answer
401 views

Nginx Configuration:504 Gateway Time-out error

We are using Nginx as a Load balancer. Nginx having IP address of :10.110.0.200 and address of host machines are 10.110.3.20|10.110.3.21 this is the configuration file: upstream test1 { server 10....