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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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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0answers
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in the case of TCP on my linux box, but on the internet you can find really different information most of which is outdated or wrong, so ...
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3answers
3k views

Lower TCP throughput from 1Gbps server than 100Mbps server over large RTT

We've got infrastructure distributed in a few major locations around the world - Singapore, London and Los Angeles. The RTT between any two locations is over >150ms. We've recently upgraded all of ...
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2answers
54 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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0answers
388 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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3answers
1k views

What port does OpenLink ODBC Driver use?

I use Avaya Reporting Services and OpenLink ODBC Drivers for db connection. I know that it uses port 5000 for handshaking but after that I believe it uses an random port for communication. I want to ...
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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
43 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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3answers
1k views

Linux: Invalid TCP Flags

It is often recommended in tutorials and books to filter invalid TCP flags with iptables. I wonder if those aren't already filtered by the kernel itself or the iptables state module. Does anyone have ...
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1answer
94 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
99 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
564 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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0answers
147 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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3answers
477 views

Why does TCP Reno cut the congestion window in half when I get duplicate ACKs?

I'm having a hard time understanding this conceptually. Why does TCP Reno cut its congestion window in half when it detects triple duplicate ACKs and cuts its window to 1 segment when it times out? ...
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3answers
8k views

What are the ramifications of setting tcp_tw_recycle/reuse to 1?

I set both tcp_tw_recycle/reuse to 1 in my configuration file. What are the ramifications of doing this? If a tcp socket is re-used, does that pose a security risk? i.e. 2 different connections both ...
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1answer
97 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 ...
86
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7answers
128k views

How to forcibly close a socket in TIME_WAIT?

I run a particular program on linux which sometimes crashes. If you open it quickly after that, it listens on socket 49201 instead of 49200 as it did the first time. netstat reveals that 49200 is in ...
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1answer
41 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
84 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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2answers
253 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
162 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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0answers
87 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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2answers
1k views

How to edit TCP window size from iptables?

There is TCPMSS target to edit MSS value of connections (including forwarded). How to edit window size (for example, cap to some maximum value) by iptables rule? Expecting something like iptables -...
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1answer
172 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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2answers
2k views

Troubleshooting High TCP Retransmit Rate

I've been attempting to troubleshoot a network issue that presents with very high rate of TCP retransmits. 36 samples (taken with Wireshark 1.10.8 running on 32-bit Windows 7) totaling a little over ...
10
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1answer
445 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
436 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....
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3answers
4k views

Monitor loopback traffic (monitor MS TCP Loopback inteface traffic) with Microsoft Network Monitor 3.4 - possible?

I've downloaded NM 3.4 from microsoft.com and it appears that the software doesn't capture traffic on MS TCP Loopback interface. When I ping 127.0.0.1 address, NM shows no packets flowing. I've tried ...
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4answers
43k views
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1answer
258 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 ...
3
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0answers
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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27 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 ...
2
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1answer
988 views

Disable kernel processing of TCP packets for raw socket

I'm working on a TCP/IP implementation, for an embedded device, that I want to test from a Linux user space process using raw sockets. raw(7) says that Raw sockets may tap all IP protocols in ...
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3answers
2k views

Windows Server 2008 - unable to bind any TCP port

OS: Win Server 2008 RC2 Windows firewall on (no effect when off) I have suddenly been plagued by an issue in which I cannot find any similar ones with a search. I am running about 20 game servers ...
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0answers
29 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
164 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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1answer
107 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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0answers
190 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 ...
4
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2answers
881 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 ...
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1answer
638 views

Openvpn: no response from server in tcp handshake

I am attempting to connect to an openVPN server that I created on pfSense 2.2.3 by using tunnelblick on my Macbook. Whenever I attempt to connect using either OpenVPN version 2.3.6 or 2.3.7 (all that ...
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0answers
49 views

TCP traffic redirection

I am using an open source program called revinetd: revinetd.sourceforge.net On server side, revinet listens for incoming connections on a defined port to act as a relay server. Now, The server ...
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1answer
89 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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0answers
88 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 ...
18
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4answers
92k views

What causes duplicate ACK records?

We're reviewing Wireshark captures from a few client machines that are showing multiple duplicate ACK records which then triggers retransmit and out-of-sequence packets. These are shown in the ...
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0answers
285 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 ...
0
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1answer
177 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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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 ...
5
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1answer
8k views

Unexpectedly shrunk window

I run a major media upload/download site and I noticed these: Is this serious or background noise due to the big file sizes and is there any tweaks I can add to /etc/sysctl.conf to improve and ...
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2answers
187 views

How to run Different congestion control algorithms in FEDORA 17?

I need to use different congestion control algorithms for tcp flow. How can I continue using those flow congestion algorithms from Fedora 11 in Fedora 17?