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 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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45 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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36 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
33 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
83 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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13 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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34 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
52 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
183 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
172 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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88 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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78 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
69 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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86 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
165 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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73 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
42 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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25 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
77 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 ...
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2answers
87 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
47 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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166 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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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
68 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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72 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
152 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
36 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
34 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
54 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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104 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
117 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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97 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
79 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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55 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
104 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
77 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
187 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 ...
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1answer
75 views

Is it possible to run 2 concurrent tcpdump with different options?

I need to run 2 concurrent tcpdump commands with different arguments/options. Why ? Because we wrote some long long scripts compatible with following options : tcpdump -ixenbr0 -s 400 -n -A 'port sip ...
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79 views

Does Fast Retransmit and Retransmission Timer work at the same time?

When Fast Retransmit is implemented, if I received packet 1, then I will send an ACK that says I need packet 2, and then if I received packet 3, I will send a duplicate ACK that says that I need ...
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21 views

Why is server refusing new connections?

One of our proprietary closed source server applications sometimes stops accepting new connection from remote nodes on its server port. Remote nodes that are already connected work fine. Any new ...
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1answer
161 views

Millions of TCP FIN-ACK retransmissions blocking traffic on my desktop machine

In a few minutes I have received about 7 millions(!) FIN-ACK packets from IP address that belongs to Google 74.125.133.188 what totally blocked network traffic on my desktop(!) machine. Other ...
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27 views

What technology do data center use to guarantee low RTT?

I was reading about data-center-tcp DCTCP and the paper was talking about the low retransmission timer (RTT) of about 250µs, but didn't state how that is being done. Somewhere else I read that DCTCP ...
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1answer
110 views

Does ColdFusion use TCP Ports?

I am trying to access a link on our network. Whenever I try, the page times out. I have discovered that this link is a Adobe ColdFusion web page. Does ColdFusion use a TCP port other than port 80? I ...
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51 views

Can I use MS Host Integration Server to connect to an IBM without using SNA

I'm sorry, this will represent a lot of information, but I'd like to avoid some of the back and forth I'm having with various forums trying to resolve this issue. So please, bear with me. I've taken ...
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2answers
301 views

better alternative for tcp_syncookies in linux

In an effort to prevent DDOS attacks I followed suggestions to leave /proc/sys/net/ipv4/tcp_syncookies value set to 1 in my linux box to enable TCP syncookies. However, when I look at this URL: ...
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1answer
506 views

Slow Upload to IIS Server

I have a Windows 2012 R2 Server running on an Amazon EC2 instance with IIS 8.5. It hosts a web application, and a custom WebDAV server that interacts with the same database as the web application. I ...
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128 views

How to fix the amount of bandwidth of iperf in tcp mode?

I'm working on some experiments about my master's degree project. I'm studying some load-balancers (I'm not supposed to cite them here) and the aim is to get for each bandwidth the cpu % usage of a ...
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1answer
82 views

How to prevent TCP network flood triggered by KVM VPS clients?

How to to protect nodes/ detect and block KVM VPS clients that TCP flood the network ? I use SolusVM VPS management system. Recently one abuser toke several VPSs and flood it the datacenter network. ...
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2answers
261 views

lsof doesn't show the established TCP connection

On my system, if I run the netstat for a port, it returns: $ netstat -nat | grep "60964" tcp 0 0 192.0.0.1:60964 0.0.0.0:* LISTEN tcp 59 0 ...
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2answers
437 views

TCP sequence number randomization

In a recent interview, my friend was asked about firewalls’ TCP sequence number randomization feature. The interviewer mentioned that we know that a firewall randomizes the TCP sequence number, but an ...