Tagged Questions
0
votes
0answers
5 views
where can I find a table of TCP header options, which lists the kind number and corresponding option
several days ago I came across a table of common TCP header options(tens of), which lists the kind number and corresponding option, now I can't find it through google.
like
kind ...
0
votes
0answers
4 views
HOW TCP get the MSS values for a certain path?
when I TCP client initiates a TCP connection with a remote TCP server, it will announce its MSS in the TCP option.
I'm at a loss how TCP knows its path MSS value. This value is specific to the path ...
0
votes
0answers
30 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 ...
1
vote
2answers
44 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 ...
3
votes
1answer
31 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
votes
0answers
28 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 ...
0
votes
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 ...
1
vote
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 ...
0
votes
0answers
31 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 ...
0
votes
1answer
41 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 ...
0
votes
1answer
60 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!
...
0
votes
0answers
27 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), ...
-5
votes
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
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 ...
0
votes
1answer
49 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 ...
0
votes
1answer
96 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
vote
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 ...
-2
votes
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
...
0
votes
1answer
54 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 ...
0
votes
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
100 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 ...
1
vote
1answer
69 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 ...
0
votes
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
599 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 ...
0
votes
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
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
59 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
174 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.
...
0
votes
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?
-1
votes
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
vote
3answers
78 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 ...
0
votes
0answers
91 views
Windows 7 cannot connect to network shares, Exchange server, Webmail… anything requiring authentication
I have been handed this Asus Ultrabook that had Outlook 2010 that was not connecting to our Exchange server. It used to when in a different office.
On our office network, it can't. I have 36 other ...
2
votes
1answer
90 views
How do I prevent connection resets upon pulling the ethernet cable?
In Windows, when you pull out (trip over it) a network cable, then the connections get reset.
If you do the same on a Linux box or if you put a switch between PC and router and then pull the cable ...
0
votes
2answers
420 views
How can i show only 127.0.0.1 traffic using Wireshark?
Every time I try to filter to just show a specific IP Address, I get an error indicating that it is "not an interface or a field." I have no idea what that means. Furthermore, I don’t really see ...
1
vote
2answers
54 views
Does TCP care about the incoming port?
Does TCP care if the port changes on a SYN/ACK that comes back compared to the destination port asked for?
I.E. If i have a port forward turning 80 into 8080, and the client sends a SYN on 80 and ...
0
votes
1answer
60 views
How to log selected tcp packet
I am troubleshooting a problem where a long TCP transaction (>=60s) would disconnect between my source (Point A) and destination (Point B), whilst passing through an internal Linux Gateway and several ...
2
votes
0answers
47 views
Most network protocols occasionally fail
My Windows 7/64 machine has suddenly started to act funny. Everything will be running fine, when suddenly most network access methods will fail. These things continue to work:
Accessing network ...
0
votes
1answer
98 views
Why does Knoppix mess up my internet connection?
I have this problem that when I boot Knoppix on my Windows box, it screws up the internet connection somehow, so Windows cannot get an IP when I reboot back to XP. I use Verizon FIOS. Normally I have ...
0
votes
1answer
64 views
Do TCP connections work differently within the same subnet?
I've encountered some network behaviour that confuses me while trying to get Java RMI working.
I use netcat to connect to a local machine:
[my_machine]$ nc -w 1 192.168.0.100 60000 && echo ...
2
votes
1answer
66 views
How does a server program distinguish between clients
Why does a web server listening on port 80 not get confused with many packets coming from different hosts. Why does it not confuse packets coming from the same host when different browsers access ...
1
vote
1answer
55 views
My sleeping process accepts TCP connections?
After sending the STOP signal to a process, it stops working as expected, but still accepts TCP connections. So is it working anyhow?
1
vote
2answers
305 views
TCP/UDP hole punching from and to the same NAT network
I was wondering if tcp/udp hole punching would still work when you are in the same network (behind a NAT), and what the packet's path would be.
What happens when using hole punching on the same ...
1
vote
0answers
69 views
TCP connection not timing out, visible on server but not client
On the server both the application and netstat show a connection open. The client however lists no such connection, and the client software is definitely stopped.
I'd already lowered the TCP ...
4
votes
2answers
473 views
How does the link speed affect TCP throughput? [closed]
Can someone explain to me how data is transmitted over a network using TCP/IP? Let's say I currently receive 500 Mbps of data over a 1 Gbps line right now. If I upgrade the line to 10 Gbps, would my ...
7
votes
6answers
2k views
Port scan revealed port 1111 open. What is it?
I am new to systems administration and have a new server running a website with http (at port 80), https (at port 443) and ssh (at port 22).
I did an nmap port scan using my personal laptop and other ...
2
votes
1answer
52 views
Can't connect to the web
I have 2 laptops. One is Windows 7 PC, another is Apple.
I also have a DSL modem and a router.
The problem is I can't connect from the Windows 7 but can from Apple.
I can ping the router without any ...
1
vote
1answer
194 views
Testing network equipment, TCP window size matters
We are currently testing some network equipment (consumer routers with 1 Gbit/s ports) with Jpef 2.0. All kinds of connection parameters are tested: wired and wireless, different wireless standards, ...
0
votes
1answer
126 views
In TCPView, what does the * mean in the Remote Address field
In TCPView what does the * mean in the remote address field.
5
votes
1answer
672 views
In TCPView, why does the svchost.exe process need to listen on so many TCP and UDP ports
Looking at TCPView I can see over 25 svchost processes using TCP and UDP ports. If these svchost processes are the various services required by Windows, then why would so many be using the network?
