Questions tagged [tcp]

For questions about Transmission Control Protocol (TCP), a transport protocol used to encapsulate data across a network for reliable communication.

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How can I connect two PCs on two different LANs with java sockets? [closed]

I know how I can connect two PCs on the same wifi SERVER: ServerSocket servSock = new ServerSocket (6666); servSock.accept (); CLIENT: Socket clntSock = new Socket ("192.168.1.8", 6666); ...
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1answer
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TCP/IP conditions to end an etabilished connection

What happens if the Client crashes and never closes the connection? Or the server crashes before being able to send a ACK FIN packet. Are those cases implemented in software?
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Can the network devices run out of ephemeral ports due to high use of websockets?

This might be a really stupid question, but something I really want to understand. My understanding is a tcp connections staying open indicates that each of the network devices between the client and ...
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1answer
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how to send a number of TCP packets and capture only those packets using tshark?

I'm using iperf3 to send 1005 TCP packets with the commands: iperf3 -s -i 1 -f m -p 5200 -D iperf3 -c 10.60.0.113 -k 1005 -bitrate 0 --reverse --omit 2 -p 5200 In server, client respectively. The ...
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2answers
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multicast udp streaming dst and src address assignment

If I am streaming on a host using the internet outside my nat, how is multcast addressing work with respect to streaming for example, if the application outside sends to 224.0.0.1 how is the packet ...
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1answer
36 views

TCP Handshaking Meaning of RST

I am trying to implement TCP handshaking but receive RST instead of ACK: No. Time Source Destination Protocol Length Info 62 24.622012890 192.168.0.147 ...
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2answers
278 views

Is TCP's MSL value equivalent to IP's TTL value?

Definition of MSL according to RFC 793: Maximum Segment Lifetime, the time a TCP segment can exist in the internetwork system. Arbitrarily defined to be 2 minutes. Definition of TTL according to ...
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2answers
249 views

Prevent TCP sequence prediction attack

Let's say an attacker gets the sequence number between me and my client. Now he continues the conversation with me and has changed the IP address. How do I prevent packages from being sent to ...
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2answers
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Modify the IP in TCP/IP packet

My ip address is specified in the ip packet sent to the next node. I wonder if a device that handles this packet can modify the ip address before forwarding it to the final destination? In theory ...
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1answer
21 views

Why we use IP address in sockets? [closed]

When a server want to create a socket, it will use a combination of its IP address and some well-known port, let us say 80. So, when a segment arrived, both the server IP and port 80 will be used to ...
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1answer
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Is it valid to send consecutive tcp packets having overlapping data?

Assuming: TCP Window Size of client: 2000 bytes MSS (maximum segment size) of client: 1500 bytes Now server want to send 3000 bytes to client B1..B3000. Server sends: Packet-1: Contains B1..B1500 ...
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1answer
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Length of Version field in IP Datagram header

I have doubt regarding length of "version" field in IP datagram. I have read the possible values are either 4 or 6 but they can represented in binary as 100 and 110, which are 3 bits in length. Then ...
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re transmission happened before receiving Three ACKs packets

In the following wireshark trace, the packet with seq=41030 was sent, after some time the packet before it got acknowledged. after that a retransmission happened the packet seq=41030, then 3 ACKs ...
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1answer
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What is the relationship between message size and message loss rate under different network delays?

I am trying to develop a real time data streaming application with different size of messages using tcp. In fault injection tests it is observed that when the network delay is less than 150 ms, ...
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How many times is the data packet copied before finally reaching the NIC? [closed]

On a typical linux machine, how many times would packets be copied from the application layer to all the way in its journey to the network card. I am assuming the protocol being used here is TCP/IP ...
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1answer
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When the first bit reaches the host B, which bit is exit from the host A?

When the first bit reaches the host B, which bit is exit from the host A?
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1answer
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What steps must be accomplished in each layer of the TCP/IP model to connect a website?

What steps must be accomplished in each layer of the TCP/IP model to connect a website?
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1answer
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Determining the sequence numbers of sent packets in TCP [closed]

I'm trying to learn TCP well from a textbook, and this is a problem that I am having trouble solving. A sender using TCP Reno (with fast retransmit and fast recovery) is going to transmit 15 packets ...
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1answer
16 views

Why and how slow clients slow Websockets (RFC 5455) network? [closed]

I want to ask why a Websocket connection RFC 6455 - https://tools.ietf.org/html/rfc6455 Usually websocket connection is fast when clients are fast enough however, when slow clients connects to it the ...
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Why does the sender assume that packet n is lost if it receives 3 back to back ACKs of packet n-1? [duplicate]

I came across an unjustified statement in my study notes regarding TCP: If sender receives 3 duplicate ACKS back-to-back, it assumes that the next packet in sequence was lost, and re-transmits. ...
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1answer
37 views

Juniper SRX Application Inactivity Timeout

Will the inactivity timeout set for the application "TCP-ALL" of 900 trump the default value of 1800 for junos-ssh if the application-set were matched in a security policy? Does it matter if the order ...
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4answers
365 views

Layering unicast addressing over multicasts

My question has to do with layering of unicast over multicast and has two parts. Part 1. IP unicast over MAC multicast First part of the question is whether there is a standard that prohibits use of ...
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1answer
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Real time video streaming over TCP [closed]

One of the topics I have been following for quite sometime is real-time streaming. Over the course of my research everyone suggested and says WebRTC (based on UDP) is the only solution to achieve real-...
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1answer
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When port-forwarding, will a port only be listed as OPEN if the service host is actually reachable?

I'm fiddling around in my lab today and attempting to learn more about port-forwarding. I've noticed that when I set up port-forwarding for a given port and run a port scan from outside the network, ...
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1answer
49 views

TCP Bandwidth and delay guarantees

I was wondering if TCP can provide bandwidth and delay guarantees? Or does it have to implemented on the application layer?
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Understanding TCP congestion control

Why is the congestion avoidance here [6,14] and [18,25]. Why not [6-10] and [18-22]? Other examples I have seen online suggest otherwise: For example here: https://www.researchgate.net/figure/TCP-...
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1answer
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Is there a difference between SYN-ACK and SEQ-ACK?

I've been trying to understand if there's a difference between the two, if any. Wireshark mentions SEQ-ACK under their TCP information of a packet, but I've typically heard this referred to as SYN-ACK....
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1answer
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Why there is a statement of FIN packet is easy to discard in the networking?

In Nmap port scan there is a Covert scanning which use FIN for scanning, but it is not accurate, because the FIN packet easy be discard in transmission. Why there is a statement of FIN packet is ...
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2answers
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Best ports to use for proprietary protocols that might get inspected/blocked by firewalls

We use software from Genesys that uses its own proprietary protocols (all TCP) and we often run into issues with customers firewalls. The ports we are using are 2000, 2200 and 3010 - I'm not sure ...
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Whether every TCP segment of Data Transmission Stage have ACK flag and ack number?

In classic TCP lifecycle, there shows every TCP segment have a flag(SYN, ACK and so on). In 3-times handshake and 4-times wave-leave, there must be flag in every TCP segment, I can understand. But ...
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Which of TCP flags will use a timer, and what Timer will use?

When I study the TCP protocol life cycle, There are 3 stages: Establish Connection Data Transmission Connection Removal TCP have 6 Flag types: SYN, ACK, PSH, FIN, RST, URG. TCP has 4 Timer: ...
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How do ACK packets get matched to SYN numbers? [duplicate]

I'm a newbie at networking, learning TCP for fun. I've been looking at packets on Wireshark, and I was wondering: How do the two sides know that an ACK packet was in response to a specific SYN packet?...
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1answer
343 views

Is TCP slow start supposed to be enabled for VoIP SIP?

TCP slow start mechanism generally is pretty useful in most cases. But it is not so good and reasonable for short-lived TCP connections. Hence the question: Should TCP slow start be used with SIP-over-...
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Confusion about TCP/IP data flow in layers

I'm confused about how the data flows through the layers of the TCP/IP model, so I'll just tell what I think it happens (using an email example) and I'd appreciate if you can point my mistakes. ...
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1answer
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What type of address is this?

As the title says I'm curious as to the type of address this is as its clearly not IPv4 or v6, yet it is using TCP.
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1answer
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TCP Checksum Calculation

I recently started with networking and tcp/ip. The RFC 793 document tells the checksum is made of: pseudo header+tcp header+tcp payload+zeroes(if not divisible by 16). So I have to take 16bit ...
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What if ACK FLAG is not set? [duplicate]

I read the RFC 793 section 3.1 , which says Acknowledgment Number: 32 bits If the ACK control bit is set this field contains the value of the next sequence number the sender of the ...
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What is the value of the Acknowledgement Field in TCP header when ACK flag is not set? [duplicate]

I am interested in knowing that what would be the value in the acknowledgement field of a TCP segment in case the ACK flag is not set? I read the RFC 793 section 3.1 , which says Acknowledgment ...
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2answers
60 views

Why can some people use public ip address to access a server from an internal network with the client device within the internal network

As the title suggests. I find it mind breaking to think how network architecture can differ to allow/not allow using public IP address to access a server within internal network from within the ...
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1answer
68 views

Which exact bytes are transmitted while TCP zero window probing?

I read the post about TCP zero window probe and it seems that such a probing segments transmit some payload. But I can't figure out which exactly bytes are sent in probing segments? Is it one (or more)...
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How does loopback address check if TCP/IP stack is correctly working or not? [duplicate]

I have been reading about loopback addresses and most of the online material says that it is used for testing purposes and it validates if TCP/IP stack is installed and working correctly. How does ...
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2answers
62 views

Best way to Fast Reconnect TCP with dynamic IP

I am aware of TCP Fast Open, all though, I'm pretty sure it doesn't apply when the IP of the server changes dynamically. Getting the IP of the server quickly isn't the problem. The problem is that I ...
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0answers
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Packets lost with correct TCP sequence number. Is it possible?

I'm analysing some communication issues that we have between a server (SCADA) and remote terminal units (RTU) that we have in the field. The communications are IEC104 protocol which use TCP/IP. The ...
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How can I configure a Cisco router 4300 to allow internal server ip:80 to be accessed on public ip:4500

I have an internal web server on port 80. I need help commands maybe to configure port forwarding to access the server on my private network from a public IP Current running config interface ...
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0answers
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Why do corporate networks prefer application-level over network-level proxies? [closed]

I was recently using an application at work, which was unable to download needed files because proxy settings were not configured for the application. The company firewall blocks non-proxy connections....
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2answers
136 views

Can TCP stand for “Transport Control Protocol”

I know it might sound like a silly question, but afaik TCP stands for transmission control protocol. However I found a couple of websites using the term Transport Control Protocol. So I was wondering ...
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1answer
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Unable to receive logs from a device to our SIEM Syslog server via TCP 514 [closed]

I want to collect logs from a security device (McAfee Email Gateway) to our SIEM Syslog server. This security device can forward logs only via TCP syslog on any port (in our case it is 514). We are ...
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1answer
44 views

How does triple handshake avoid establishing connection for duplicate packets(coming later down the line)

The idea behind triple handshake seems to be for duplicates to not cause issues. The way I understand it host sends a sequence x to server. Server acknowledges it and sends it's own sequence y. Host ...
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1answer
77 views

Do sequence and acknowledgment numbers treat 3-Way Handshake differently?

1- Just as the message ID that is assigned to each message in PAR, the "sequence number" is a means of providing reliability in a transfer of a byte stream. So sequence numbers are assigned to every ...
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latency in the network layer and transport layer [duplicate]

We have several way to measure latency (ping command (ICMP packets), hping(TCP SYN), iperf..).What is the difference between measuring the latency in the network layer and measuring in the transport ...

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