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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25 views
Can anyone explain how the loopback interface works? [duplicate]
I got to understand how TUN/TAP works from the following illustration:
TUN/TAP illustration
I'm at a loss how the loopback interface works. Can anyone explain a bit about how the loopback interface ...
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2answers
34 views
If there are 2 NICs on the same machine, can a TCP client on one NIC connect to a TCP server on the other NIC?
I use TUN/TAP to create a tun NIC tun0 with IP 10.10.10.2, and I have a real NIC eth0 with IP 202.112.34.49
Then I run a TCP client which binds its socket to 202.112.34.49 and a TCP server binding ...
1
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1answer
22 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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1answer
52 views
The best way to do TCP/IP over USB on Linux
I want to establish a TCP/IP link between two Linux machines that have several USB 2.0 ports as the only connection options. Since both host and slave ports are available, I can connect them via a ...
3
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1answer
29 views
TCP header option: SACK-permitted (Selective Acknowledgments) negotiation
I'm doing a research project, which needs to split tcp connection.
so I have some pecular questions, which may happen in my development.
The problem is understanding of TCP SACK-permitted ...
1
vote
1answer
16 views
is it possible to update tcp window scaling factor after 3-way handshake by sending a syn/ack?
tcp window scaling factor is notified during 3-way handshake period
is it possible to update tcp window scaling factor after 3-way handshake
for example, by sending a SYN/ACK with tcp header option ...
4
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0answers
25 views
What type of TCP connections are counted?
In Windows 7's Resource Monitor, in the TCP Connections graph at the top right -- how are those connections being counted? Does a "listening" state count, for example? Does it matter what state a ...
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2answers
26 views
Port forwarding beginner
I have been trying to set up port forwarding for the past 48 hours and I can't quite get it. I have used online port scanners to see what ports are open and they are saying none, not even the port I ...
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2answers
29 views
Sending TCP command from external network to specific device in home network
I'm working on a mobile phone application which has to send a TCP command to from external network (like a coffee shop or it's connecting to 3G) to a specific device in home network. Let's say
A ...
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1answer
42 views
DNS: can't dig 8.8.8.8 directly
me@ubuntu:# dig @8.8.8.8 google.com
; <<>> DiG 9.9.2-P2 <<>> @8.8.8.8 google.com
; (1 server found)
;; global options: +cmd
;; connection timed out; no servers could be ...
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0answers
30 views
can firewall send RST packets in response to a TCP SYN?
I used tcpdump to capture packets on a host 6.23.33.44 when a program on it sends some TCP packets, these TCP packets are crafted using raw socket. So, actually there is no tcp connection between ...
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1answer
38 views
Scapy: TCP Retransmission error
I've been using Scapy to send SCCP or Skinny packets to my Cisco Desk Phone. However I keep getting these TCP Retransmission errors, and I believe this is causing the Cisco Phone to not respond. I ...
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1answer
56 views
MTU, RWIN, and MSS
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!
...
1
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0answers
15 views
How to use NetLimiter to block inbound TCP traffic?
I'm using NetLimiter to block TCP traffic. (Rule type: Firewall, Direction: In, Action: Deny)
I can block outbound, but not inbound. You can try blocking inbound TCP on Chrome to see it is not ...
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0answers
23 views
how tcp stack deal with the ack_seq number and seq number of tcp FIN/ACK packet?
from my knowledge, seq and ack_seq are processed by tcp stack independently.
when a packet arrives with a inconsistent ack_seq number
if: 1) the ack_seq number is obsolete(smaller than expected), ...
3
votes
1answer
30 views
Automating an IP Phone
I've been very interested in Automating an IP phone, currently I am automating phone calls by using PuTTY to a Dial-Up modem through simple AT commands. However, this is a poor method because it does ...
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0answers
13 views
Windows Vista SP2 firewall blocks ports again
My System is using all available updates / patches.
I am developing of server software which open a specific TCP port, so the Vista firewall asks for permission which I grant.
Later I start a ...
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0answers
22 views
Do routers block out going TCP client connection requests ? [closed]
I want to know if routers block client connection requests that which try to connect to a TCP Socket which is hosted on Internet
Please tell me some details
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1answer
80 views
Can't connect to SSH over VPN when using 3G only
I'm having a bit of a strange problem that I'm not sure how to debug/fix. I have a Raspberry Pi connected to a Windows VPN via either a wired interface or 3G dongle. With the wired interface I can ...
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2answers
47 views
TCP Throughput versus Packet Loss
How does the packet loss rate affect the TCP throughput rate: throughput rate reduce exponentially with respect to loss increase or throughput rate reduces by the same amount as loss increase?
2
votes
1answer
34 views
find the process which is listening on a specific port
I want to find some processes which are running on a specified port
for example 80
I ran
fuser 80/tcp
and got nothing
and then
netstat -tulpn|grep "80\|PID"
and got
Proto Recv-Q Send-Q Local ...
3
votes
3answers
78 views
How to pipe data over tcp from the command line?
I would like to pipe data from one machine in the command line to another machine over tcp. I guess I could write a socket server but this must already be implemented. For example I could use it to xz ...
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1answer
46 views
using iptables to prevent RST related to a specific port
I have a program which uses libpcap to capture incoming TCP SYN packets, these SYN packets are destined for a specific port.
But I have no tcp listening socket for that port, so in practice, the OS ...
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1answer
93 views
Why is my UDP so slow?
I'm using Iperf on two VMs and when using TCP I find the performance is as follows:
notroot@ubuntu:~$ iperf -s
------------------------------------------------------------
Server listening on ...
1
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1answer
47 views
Is it possible for a PC to use two net connections simultaneously?
We have two net connections in our office - a 10mb Wired DSL provider and a 3mb Wireless backup provider. The wireless is a backup, but it has the advantage of 3mb upload speeds whereas the wired is ...
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1answer
31 views
is it possible to create a server which can receive different packets from a specific port [closed]
I want to run a server process on a computer, it is binding to a port
and then I want to process can receive all packets that is destined to that
specific port
and then I want to parse the packets
...
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1answer
53 views
How do NAT or proxy react to incoming TCP SYN packet?
In some messaging systems, two messaging clients send/receive packets directly from each other in chatting or voice call. I think the basic mechanism is (TCP for example): these client programs open a ...
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0answers
18 views
running ab multiple times slows requests down, how to diagnos this?
I have a simple website that I run apache bench with like:
ab -n 10000 -c 10 -k http://localhost:8080/
After running it once, the second time around the responses slow down allot.
How can I ...
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0answers
22 views
Can't establish Reverse tcp connection while launching exploit
I'm running a pen testing with two machines: BT5 and Win 7. Both of the machines are sitting behind a NAT (192.168.1.x) and can ping eachother. Each time I tried to exploit the Win 7 with Client side ...
0
votes
1answer
24 views
No Internet access when second dial-up connection in Windows 7
I have a dial-up connection set apart from my normal internet access. When I connect to that dial-up , I loose Internet access (from the 1st network). When the dial-up is not active, Internet works ...
1
vote
1answer
90 views
Virtual Windows Server 2008 R2 system unexpectedly responds on TCP echo port 7
We have a virtual system running Windows Server 2008 R2, and it responds on TCP port 7 (echo). (I.e, in response to a SYN it sends ACK,RST, which is enough to make InetAddress#isReachable() return ...
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0answers
67 views
what is the difference between TCP ACK packet and TCP DATA packet [closed]
I see that in TCP DATA packet,
there are two possibilities,
1 PSH and ASK is set
2 only ACK is set
for 2, if the data field is null, I mean the data length is 0,
it degenerate to an ACK packet, is ...
3
votes
0answers
98 views
intercept TCP/UDP Packets on a host before they are sent to or recevied from the network [closed]
for example,
1
when I'm using some programs, like visiting websites using firefox
if the webserver send my program some data, my program TCP stack will issue
an ACK packet. Is it possible to ...
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0answers
25 views
Win7 firewall does not respect inbound rules
The win7 firewall blocks port 9000 tcp even if I set the inbound rules. What could be the problem?
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1answer
61 views
is tcp header timestamp mandatory or optional? and how to generate tcp timestamp
I noticed that in all tcp communications,
in the tcp header option parts, tcp timestamp is always there
is it mandatory or not?
so if there is no tcp timestamp in a tcp packet, the tcp client or ...
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0answers
28 views
Secure TCP based protocol through an application layer firewall
I have two networks, one considered secure, lets call it A and one considered insecure, B. The software I need to use, uses HSMS, a protocol based on TCP with no security built in.
Now the problem is ...
2
votes
1answer
571 views
How is TCP/UDP checksum working?
I used raw socket to create some UDP packets
and then send them to a UDP server
I notice that when I put a wrong UDP checksum number
the UDP server doesn't accept it, but if I put all 0 on the ...
1
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0answers
83 views
tcp port numbers reused on wireshark
I used raw socket to build a tcp client program on machine A to reproduce tcp 3-way handshake with a simple regular tcp server on machine B
I captured packets on the client host and server host, and ...
0
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1answer
47 views
sent packet is different from received packet
I use raw socket to create TCP packets, with focus on the sequence number and TCP flags(SYN, ACK)
I used one machine S to send a tcp ACK packet (flag ACK is set to 1)
and another machine R to receive ...
0
votes
0answers
38 views
how to block rst, ack packet on windows 7 x64
As the title says, I my trying to block a specific RST, ACK packet coming from my win7 machine. My machine is Win 7 x64, but all the firewall solutions I have seen so far (wipfw, pcktfilter) all seem ...
0
votes
1answer
41 views
Simple program to turn a server into a client and vice-versa?
What would be a simple to use program for Windows that would do the following:
Computer A unknown TCP client wants to connect to computer B's unknown TCP server.
Both are behind a NAT.
Computer A ...
0
votes
1answer
58 views
TCP number of connections differ from client to server
How can this be ? netstat shows x 'established' connections from the client to y 'established' connections on the server. Situation stays like this for 10 minutes, then x and y change, then another ...
0
votes
1answer
55 views
How does the browser know which packet is the response to a specific request?
I am sniffing the in/out packets over TCP. I have some GET output, but I want to know which of the packets is the input? How does the browser determine this?
Simpler explaination: I'm sniffing and I ...
1
vote
1answer
58 views
What does this tcpdump printout mean?
I'm not very experience with networking, so on my free time, I usually try and learn some more things about the internet and how it works. While at school, I came across tcpdump and wanted to give it ...
3
votes
1answer
168 views
Is there a way to kill an open connection without killing the process?
I've search around and all the suggestions just say to kill the process. But I'm surprised I can't find any simple way to force a "connection" to close, without killing a pid associated with it.
...
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votes
1answer
24 views
What is the “-nolisten tcp” parameter for X
I have just found that my latest kubuntu comes preconfigured with the following:
in directory /etc/X11/xinit there is xserverrc
#!/bin/sh
exec /usr/bin/X -nolisten tcp "$@"
But the -nolisten tcp ...
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0answers
98 views
Artificial network delay tcp/udp (bigger ping) for defined application? (windows)
I have a game where people can easy detect who i am looking at my ping, i want to make my ping highter.
How can i set network delay for all network connections for defined application?
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1answer
48 views
What happens if i send html over tcp without using the http protocol? [closed]
Will the html be delivered properly to the browser, or will it lack formatting? Will it get delivered at all?
1
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3answers
76 views
Is the following analogy to describe the relationship between TCP and HTTP correct?
TCP as a hose-pipe and HTTP as the water flowing through it
I've just been reading some, and trying to conceptualize the difference between TCP and HTTP. I stole the analogy from here ...
1
vote
2answers
225 views
Get the current/default value of TCP initcwnd on Linux
I can manipulate such value with:
ip route change ... initcwnd 10
and then have a feedback with:
ip route show
But what about the default value before any modification? Is there a way to query ...
