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.

learn more… | top users | synonyms

1
vote
1answer
22 views

What are the default nmap options?

Which options are used by default, when the user fires # nmap target without any explicit option? I am going to write the defaults of the three options I consider the most important. It would be ...
0
votes
1answer
24 views

how can i get SYN & SYN+ACK value for current tcp connection of any website on Browser?

As I know that '$sysctl | grep net.ipv4.tcp' gives the system wide TCP parameter value,I need to make a script in Bash for my college practical file in which If we open Browser and input the ...
-2
votes
4answers
105 views

Why do computers have 65,535 TCP ports? [closed]

Why do computers have 65,535 TCP ports? Where does this number come from? What does it represent?
2
votes
1answer
30 views

How get the value of TCP connection establishment timing,retry timing in ubuntu 14

how i get the value of TCP connection establishment timing ,retry timing for any TCP connection and also Quality of services parameters in Ubuntu .
3
votes
2answers
49 views

IPTables - Redirect traffic based on country

Is there any way how to allow TCP traffic only from specified countries on a specified port and the rest of traffic redirect to another IP/port using iptables ?
1
vote
1answer
19 views

Wireshark's reassembled PDU consists of TCP segment size > MSS?

I'm looking into a Wireshark record provided by someone, to analyze something for them. Wireshark has conveniently reassembled 3 TCP segments that all transported a single TLS packet. The TLS packet ...
0
votes
1answer
17 views

TCP connection with multiple proxies in between

Client sends an Proxy-Connection: Keep-Alive header, the intermediate smart proxy sees this header and replaces it with Connection: Keep-Alive and sends to the web-server. All good and fine. What if ...
0
votes
1answer
23 views

are TCP connections made while typing the URL

Do browsers make TCP connections while typing the URL in address bar? I launched nettop utility, and was surprised of how active my connections are, even while only typing an address and not visiting ...
1
vote
1answer
12 views

Tcp Re-transmission timeout in a very short time?

I have two Windows 2012 R2 machines (122 and 115) hosted on the same VMWare host. We have a heartbeat at application layer between those two machines, from time to time there will be tcp ...
1
vote
0answers
20 views

Strange response from a HTTP server

I noticed an unfamiliar device when scanning my local wireless network. It had two open (listening?) TCP ports; TCP/80 (http?) & TCP/443 (https?). In an effort to identify the unfamiliar ...
0
votes
0answers
16 views

Unable to find traffic for specific device w/ Wireshark (over Wi-Fi)

I have a device communicating with a TCP server running on my machine. My machine is normally connected to the network via ethernet, however I also have a wireless adapter that I can use to connect to ...
0
votes
0answers
11 views

Direct host SMB - Ports

It's well known that SMB uses port 445, and that NetBIOS uses ports 137-139. However, according to all official MS documentation (https://support.microsoft.com/en-us/kb/204279), SMB uses both TCP and ...
0
votes
0answers
36 views

TCP congestion control

I was curious to know which are the default TCP congestion control method used in latest version of MacOSx, linux kernal, windows 8, windows 7 and windows xp. Does it use newreno or anything newer?
0
votes
1answer
12 views

DrayTek Vigor 2830 open port issue

We're using a Vigor2830 for routing VoIP/SIP traffic. One of the ports required to be open is 5090 for TCP/UDP. Going into the open ports section of the Vigor menu we have opened all the ports ...
0
votes
1answer
7 views

Reason for TCP Slow Start in Subsequent Connections

From my understanding TCP slow start is used to compensate and prevent congestion and loss. When a connection is successfully established and used for a while, the bandwidth of the TCP connection is ...
0
votes
0answers
8 views

pfSense does not close connections coming from LAN

I created a NAT rule that redirects external_ip:1234 of modem (pfSense itself) to 192.168.1.100:1234. I also wrote a server application which listens for connections on 192.168.1.100:1234. When I ...
0
votes
1answer
50 views

Socat not closing tcp connection

I use socat 1.7.3.1-r0 and run following command on an alpine 3.3 linux server: socat -d -d -d PTY,link=/dev/ttyFOOBAR,echo=0,raw,unlink-close=0 TCP-LISTEN:7000,forever,reuseaddr Socat will listen ...
0
votes
1answer
13 views

Connecting from WAN to LAN

I'm developing an app for my family that uses sockets to comunicate between devices in LAN or WAN. As IP addresses change constantly I am planning an FTP server for address book and TCP/IP for ...
0
votes
2answers
24 views

TCP: Disable pure ACKs?

I have a scenario where I wish to disable pure ACKs (TCP ACKs with no data), but I can't find how to do this. Is there an option that I can set so that ACKs are always piggybacked onto the next data ...
0
votes
1answer
46 views

ping works but iperf3 doesn't show any traffic for TCP

machine A has IP (eth0: 192.168.1.1, eth1: 10.10.xxx.yy) machine B has IP (eth0: 192.168.1.2) A and B are connected through RJ5 on eth0, both sides. ping works fine on both side, but when running ...
-2
votes
2answers
65 views

Why game latency fluctuates aggressively during day?

I play World of Warcraft (uses TCP) from India, on a server located in France. I get 180-200ms in-game past midnight which is quite comfortable for me, and unfortunately the best I can get due to the ...
0
votes
0answers
23 views

How to add latency to TCP packets?

I have tried netem and wanem neither seem to be affecting the TCP packets. How can I add latency to TCP packets?
1
vote
2answers
42 views

RST sequence number and window size

RFC793 states the following about RST processing: In all states except SYN-SENT, all reset (RST) segments are validated by checking their SEQ-fields. A reset is valid if its sequence number is ...
0
votes
1answer
29 views

Can two different applications bind the same port on a host if they use different protocols?

 my question is quite clear I think. If two applications use different transport layer protocols (e.g. TCP and UDP or something else) can they open the same port number? How does the OS do the ...
0
votes
0answers
15 views

tcp sesssion duplicate acknowledgement and retransmission

Please help in understanding why the receiver keeps sending duplicate acknowledgement yet the senders keeps sending old packet sequence (re transmitting of old packet seq)
0
votes
0answers
23 views

Duplicate and retransmission

Please help me understand why the receiver keeps sending duplicate acknowledgements, yet the senders keeps sending old packet sequence (re-transmitting of old packet seq) in the below capture: Please ...
0
votes
1answer
18 views

A bunch of tcp unseen segments and duplicates on wireshark?

Recently, my Mac has been unable to use the internet well. Even though it said my ping was between the ranges of 10-20 ms and my download speed was around 20 Mbps along with around a 10 Mbps upload ...
-1
votes
1answer
38 views

TCP RST Connection - Netflix - Only on Linux

I wouldn't have asked this here, but I am at wit's end, this makes absolutely no sense at this point. I have been trying everything. I have a single iptables rule: -A POSTROUTING -o eth0 -j ...
0
votes
0answers
45 views

Drop resilient tcp tunnel

I'm looking for a tcp tunnel that can provide connection drop resilient TCP connections to my VPS. Currently when I have some tool connected to my VPS and I switch from Wifi to LAN or my internet dies ...
0
votes
0answers
111 views

No connection could be made because the target machine actively refused it

On Windows machine, I start a server on port 62325 $ netsh firewall show state shows: Ports currently open on all network interfaces: Port Protocol Version Program ...
3
votes
1answer
78 views

Is it necessary for an RST packet to have an acknowledgement number?

I am studying about TCP reset attack. I know that some RST packets have an acknowledgement number (with the ACK bit set), and some RST packets do not have an acknowledgement number (the ...
1
vote
1answer
20 views

Acknowledgement number of an RST packet

This question states that the acknowledgement number of an RST packet should be 0, but I have found it to be other than 0 when I captured some HTTP packets using Wireshark. So when does the ...
2
votes
1answer
15 views

Can't get windows host file to forward HTTPS headers

I'm currently trying to write a proxy in C# using the host file to redirect requests (specific request). I only want it to intercept one address. It's on Windows and the proxy is run locally on the ...
0
votes
0answers
24 views

Still Lost on Blocking TCP Port Connections form Terminal

I'm still not 100% understanding what to do in Terminal to block certain URLs for specific ports. And I don't want to use Little Snitch. I really want to wrap my head around this. So if someone can ...
2
votes
2answers
92 views

Send TCP with incorrect checksums

I'm having trouble sending large files to an OpenStack machine. Our Internet connection is over LTE so bad packets are to be expected. However, even sending data over TCP results in corrupted data ...
-1
votes
2answers
39 views

what distinguished OSI from TCP/IP in practice?

so i am going through cisco ccent/ccna. working through the text on my own just for general useful knowledge. so in the early part of the book it goes into describing the different layers of the ...
0
votes
1answer
37 views

Close a TCP connection using nmap

I am trying to close connections in command line. For instance, I am trying to close my SSH connection with this Nmap command: $ sudo nmap -p 22 --scanflags RST <mySSHServerPublicIP> $ sudo ...
1
vote
1answer
20 views

Where do I start to troubleshoot this strange activity from my firewall?

I noticed that my firewall yesterday blocked outgoing attempts starting at port 61494 and worked its way up to 62381, making a TCP outgoing attempt at each port once. The remote IP address seems ...
0
votes
0answers
22 views

TCP and UDP do not work with firewall

I can not connect my TCP-Client to my TCP-Server. Here is my Code: http://stackoverflow.com/questions/35661591/tcp-server-does-not-work-with-firewall I have already opened my TCP-Port "8888" in the ...
0
votes
2answers
34 views

During queuing delay, do TCP, IP, and Data Link headers act as a packet or 3 different packets?

According to the definition from wikipedia, I found processing delay to be the delay caused by router processing the packet header. I am just wondering are TCP, IP, and Data link Headers all ...
-2
votes
2answers
40 views

Why ICMP is different that TCP and UDP? [closed]

what is the difference between Internet Control Messaging Protocol over Transmission Control Protocol and User Datagram Protocol
0
votes
1answer
48 views

Can HTTP deliver video over the internet or is that TCP?

The post below talks about delivering video content to users via HTTP. Is it confusing it with the TCP protocol? ...
0
votes
0answers
53 views

How to simulate TCP simultaneous open and close conditions?

I am learning TCP/IP protocol. I want to see simultaneous open, close, half open/close, etc conditions in practice. I have created simple TCP server and client program. How can I simulate simultaneous ...
0
votes
0answers
46 views

Is there a way to completely disable TCP keepalive?

I'm trying to disable TCP Keepalive in a linux machine. If I set the three keepalive parameters to 0, the machine refuses connections. sysctl net.ipv4.tcp_keepalive_time=0 sysctl ...
0
votes
0answers
14 views

Ubuntu IPTables

I started hosting my game-server on Ubuntu Linux 14.04 I am having an issues ، some enemies/bug abusers log in 2+ characters in the same second then they spam a certain spell/word that lags/stops my ...
0
votes
0answers
23 views

How to know that I passed the firewall from the TCP connections?

In my company, in order to access some intranet-sites, I have first to login to webpage (which I suppose is a firewall or something) with my account. If I login from FF for example, I can access the ...
0
votes
0answers
47 views

NAT doesn't allow TCP ACK for sent TCP SYN

We are using TCP Simultaneous Open for connecting TCP socket. Lets call one SideA and other SideB. From the wireshark log I see that first two SYN sent from SideB is blocked by SideA NAT. Then SideA ...
0
votes
2answers
42 views

How does a Router/Modem obtain the Port Number from an IP Datagram?

The IP datagram header is a layer below the TCP segment which contains information on the port. Therefore before a firewall can inspect a port number, must the IP datagrams be rebuilt into the TCP ...
0
votes
0answers
24 views

Wireshark FTP multiple ACK?

I'm trying to visualise somes frames that correspond to a file transfer between two machines on Wireshark. The thing is that there are multiple ACK for each FTP-DATA segment and I don't understand ...
0
votes
0answers
65 views

Replay captured TCP packets

I captured a tcp traffic using wireshark and saved the traffic in pcap file. I did two tests: Test 1: sudo tcprewrite --infile=capturedtraffic.pcap --outfile=temp.pcap ...