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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RabbitMQ message broker unable to open unused port 61613

On a Windows Vista system, RabbitMQ fails to open port 61613 which is not used (as netstat and TCPView show). The server log indicates that it is possible to bind port 5672, but the next lines show ...
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5answers
5k views

Server not sending a SYN/ACK packet in response to a SYN packet

Using iptraf, tcpdump and wireshark I can see a SYN packet coming in but only the ACK FLAG is set in reply packet. I'm running Debian 5 with kernel 2.6.36 I've turned off window_scaling and ...
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2answers
109 views

How can I release a port that is still in use but not bound to a process?

I'm running a Python application that spawns multiple processes. It uses port 56008 to listen for client requests. Sometimes after closing it the port it used is still "in use". There are still some ...
3
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1answer
412 views

How to expose a UNIX domain socket directly over TCP

I'd like to have a UNIX domain socket, say /var/program/program.cmd for example, exposed via TCP, lets say on port 12345. I'd also like this to be running full time in the background. What's the best ...
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0answers
40 views

IIS6 poor throughput from higher latency

I've been having a crazy issue with Windows 2003 + II6 where the throughput goes down as the latency goes up. This is exactly the type of thing that TCP Window scaling is supposed to solve so I ...
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2answers
165 views

Can a duplicate computer name be known before attempting to join the domain?

Techs in the field are deploying windows 7 pcs onto a domain. They complete one entry screen, which should give them a unique computer name. However, they are human and end up giving the pcs the ...
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0answers
964 views

How do I prevent TCP connection freezes over an OpenVPN network?

New details added at the end of this question; it's possible that I'm zeroing in on the cause. I have a UDP OpenVPN-based VPN set up in tap mode (I need tap because I need the VPN to pass multicast ...
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1answer
4k views

Why does WireShark think this frame is a TCP segment of a reassembled PDU

Please find a small pcap file here illustrating my problem. I have a three-way TCP handshake, followed by two FIX logons. (FIX is a protocol used in trading.) The first FIX logon (frame 4) is ...
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1answer
56 views

TCP Implementation in Micrsoft Windows XP + 7 [closed]

I'm looking for the TCP implementation in MS Windows, especially for Windows XP and 7 in case they are different. To be more specific, I'm interested in the following parts of the TCP implementation: ...
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2answers
180 views

Linux : Send a tcp message to a url/endpoint [closed]

I want to send a xml message to a URL like tcp://localhost:6060/services/test What are the available tools for this?
3
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1answer
181 views

Enabling TCP md5 signature option in centOS?

I'm trying to enable md5 checksum/signature for tcp packets in centOS (the main use case to stop tcp RST attacks, etc). It seems like I may be able to do this for individual ports using netcat or via ...
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1answer
86 views

can I filter TCP SYN packets with seq=0

My servers appear to be targeted by a SYN-flood attack. Between 50-600MBit/s, spoofed IPs. Packets look like this: IP p.q.r.s.1234 > my.ser.vers.ip.80: Flags [S], seq 0, win 5840, length 0 with ...
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1answer
706 views

Newbie, need help deciphering firewall log files (Cisco ASA 5520)

I'm not very familiar with firewall log files, or many of the terms involved in server connections. The lines in question involve a foreign, unauthorized IP interacting with a firewall (Cisco ASA ...
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3answers
94 views

TCP application accessible remotely but not locally

I am trying to help a friend figure this out, so I don't know all the details, but I figured I would post on here to see any possibilities. We have a custom application that communicates using a ...
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0answers
80 views

Only ICMP traffic allowed inbound on ISA Server 2006

I have recently set up a connection to a remote site. The connection between the sites is done at the ISP level (ie, this is not a B2B tunnel on ISA). I'm fairly lightweight in the networking realm, ...
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2answers
1k views

server will not reply (syn -ack)

I like to use the following commands to manage 'TIME_WAIT', in the hope to free up resources. echo 20 > /proc/sys/net/ipv4/tcp_fin_timeout sysctl -w net.ipv4.tcp_tw_reuse=1 sysctl -w ...
2
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2answers
93 views

Minimal size of TCP communication

I am sending small amounts of data (up to 100 bytes) every 10 minutes from devices to TCP server. In my case overhead seems to be huge (we pay for each byte). I found that I have at least 7-10 packets ...
20
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5answers
17k views

How passively monitor for tcp packet loss? (Linux)

How can I passively monitor the packet loss on TCP connections to/from my machine? Basically, I'd like a tool that sits in the background and watches TCP ack/nak/re-transmits to generate a report on ...
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1answer
113 views

How do I change the source address of a tcp packet?

Is it possible to change the source address of any TCP packet ? I am aware of the fact that I will not receive those packets if I change the address, I only need to place a request on the server. How ...
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2answers
2k views

TCP connection stuck in SYN_RECV state despite ACK received, Linux 2.6.18, embedded, ARM

My client cannot connect to my protocol port (TCP) after some network glitches, even though all other protocols (telnet/HTTP/FTP) work fine. netstat shows that my server is listening and tcpdump on ...
3
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1answer
409 views

How to debug why WAN TCP/IP throughput is lower than expected?

I'm trying to figure out why tcp/ip throughput between two hosts I control is much lower than expected. Host A: internet connectivity provided by Comcast (Residential) in Boston Metro -- can ...
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1answer
139 views

Can't connect to my own machine through public IP

I couldn't figure out why I can't make a connection through my public IP. When using a local IP it works. I have the proper firewall port exceptions, and my router NAT has the configurations for port ...
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2answers
4k views

A lot of TCP: time wait bucket table overflow in CentOS 6

we have the following output from dmesg: __ratelimit: 33491 callbacks suppressed TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: ...
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1answer
48 views

How to host a TCP / UDP service on the Internet which is currently running on my local machine? [closed]

I have created a TCP server and it's currently hosted on my local machine, but I want to host it on Internet like we host websites. Is there any company which provides this service? And what's the ...
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1answer
82 views

Will traffic control software cause tcp packets to be dropped

I am testing our client-server applications using NetLimiter which is a traffic control software. I found that, when client is receiving files from server and I use NetLimiter to set the download rate ...
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3answers
189 views

Max client TCP connections through a router

I've just been thinking about what the maximum number of client connections would be out of my home LAN to a single server on the internet. My home router is also NAT'ing the connections to convert ...
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1answer
117 views

Socket based byte counts

I see a lot of tools to get the RX and TX byte counts for transmission on interfaces, is there any tool/program that I can use to get a total transmitted byte count for a single specified socket? I'm ...
2
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3answers
742 views

Why is it 3-way-handshake and not more?

TCP uses the 3-way-handshake mechanism. I understand how it works pretty well but I wonder why it's not 4, or even 5-way? Is it because that's too much overhead and is not needed?
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6answers
16k views

How to capture ack or syn packets by Tcpdump?

I want to know the filter rule , thanks!
2
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2answers
1k views

Reduce firewall rules by half - one iptables rule for tcp and udp

I have a number of iptables rules on my firewall that look like this: iptables -A zone_lan_forward -p tcp -d 1.2.3.0/24 -j ACCEPT iptables -A zone_lan_forward -p udp -d 1.2.3.0/24 -j ACCEPT Is ...
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4answers
510 views

Rsyslog not logging from remote server

I am trying to set up a centralized log server. I have central server (A) receiving logs via a remote server (B) on port 514. I know it is receiving these. Here are a few entries from a tcpdump on ...
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1answer
93 views

Minimal handshaking necessary before establishing TCP connection

I have a Windows PC that is running a TCP server on port 9000. I also have an FPGA which is directly connected to the PC via a 10G port. The FPGA can send ethernet frames to establish and maintain a ...
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4answers
243 views

Why is the TCP checksum inverted?

From the Wikipedia page: The checksum field is the 16 bit one's complement of the one's complement sum of all 16-bit words in the header and text. Why, after summing the 16-bits in the header ...
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1answer
149 views

How to disable Xvfb using TCP ports when using pyvirtualdisplay (Python)?

Trying to use pyvirtualdisplay for Python to start some applications with a virtual Xvfb X terminal. However, we've seen port clashes and would like to disable Xvfb from using TCP ports. I have ...
2
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0answers
262 views

How to force use of tcp instead of udp for rpcbind?

I'm trying to use tcp/111 for rpcbind under Debian Wheezy instead of udp/111. The portmap in Squeeze uses tcp/111 without any special configuration, but Wheezy fails. Even numerous sites (as well as ...
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2answers
176 views

TCP vs UDP Error-Checking

I've bounced upon two articles that describe in-depth on how TCP and UDP connections work. However there is some kind of inconsistency. Where one article tells me that UDP does no Error-Checking at ...
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0answers
86 views

tcp recycle and retransmission

TCP recycle reduces TIME WAIT by reusing sockets. It avoids collision with older packets by storing timestamp and receives packets with greater TCP timestamp. What happens when the client retransmits ...
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1answer
86 views

What process does 'own' socket in 'Time Wait' state?

Main question I see following line in netstat. Does it means this socket doesn't belong to any process? #>netstat -tpn|grep TIME_WAIT| head -1 tcp 0 0 ::ffff:127.0.0.1:5555 ...
2
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1answer
676 views

Tuning tcp_keepalive_time for Node.js leak

I'm currently having a socket leak with my Node.js application. This bug is also posted here. I hope to fix this soon. CLOSE_WAIT and FIN_WAIT2 seem to be the major problem. Connections: 1662 ...
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2answers
158 views

IP and Port Forwarding on ASA 5505

I have an ASA 5505 with outside network of public ips 95.123.234.64/26 and inside network of private ips 10.22.33.0/24. I would like to redirect any tcp traffic that hits 95.123.234.67:80 to a public ...
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1answer
156 views

TCP RWIN, MSS and MTU [closed]

I have been doing some reading into TCP Receive Window (RWIN), Maximum Segment Size (MSS) and Maximum Transmission Unit (MTU). Right off the bat I have some questions and I need a power user's help! ...
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1answer
97 views

svnserve -d child process spawning and svn connections under netstat

I see many svnserve -d processes running on my CentOS 6 box, one with the PID 400 and PPID 1 and the rest with PPID 400. I take this to mean the first one is started by init scripts (i know it is) ...
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0answers
335 views

Client does not send ACK after receiving SYN,ACK from server

The question is that my application does not send ACK packet after receiving SYN,ACK response from server. I've managed to get dump when using different connection, but i could not find any critical ...
0
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1answer
131 views

TCP/IP routing: accessing a LAN device with wrong static IP configuration

I forgot to change the static IP of a network device before moving it from my datacenter network to my home LAN. Since it isn't configured properly for my LAN network, I'm not sure how to access it. ...
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0answers
67 views

Cant connect to mysql server

I'm trying to configure a freshly installed mysql server to listen on port 3306. I've removed skip_networking, I have changed bind-address=172.20.33.1 (which is my server ip) and it completely ...
8
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1answer
220 views

Where can I embed proprietary information in a layer 2 or layer 3 packet?

The Citrix Netscaler has an interesting property that embeds information in the TCP packet that gets sent to the host. This property is echoed back to the Netscaler in such a way that the Netscaler ...
2
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1answer
2k views

How to increase maximum connection backlog limit in windows 2008 server

I have a Windows 2008 Server. Its maximum connection backlog limit (TCP) is 200. Is there any way to increase this limit to a higher value – say 1000 or 2000? In this article you will find ...
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0answers
199 views

How to interpret findings on TCP Send/Recv Buffers

I have an application running on a CentOS machine that connects to a remote DB server on another CentOS machine. Every once in a while, without any discernable warning signs, the application seems to ...
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0answers
75 views

reset packet sent when receiving big TCP traffic

A client receives chunks of TCP segments from a server, which total 20MB or more. Sometimes the client will send RST segments to the server before terminating the TCP connection. Before sending RST ...
2
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2answers
121 views

Is TCP RWIN set by application or OS?

I have a situation where an application is listening on a TCP port and every once in a while, as seen in tcp dumps, gets its Receiving Window (RWIN) set to zero. When this happens, its Recv-Q stops ...