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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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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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3answers
56 views

Analyzing TCP connection by running Wireshark in two endpoint

I am trying to find the number of lost packets in the network. I have 2 devices say DeviceA and DeviceB. IP addresses are respectively DeviceA : 192.168.0.104 and DeviceB: 192.168.0.105. In order ...
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1answer
49 views

What will be the behaviour of TCP in a case when application layer is changed to send small packets

Assume I have an application layer protocol that segments the packet itself. So if it has 100 MBytes of data, then it will divide the data into 10000 segments and send each segment individually to TCP....
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TCP Payload vs Cellular Data Usage

I have a device that connects to the AWS via a LTE CAT1 modem. In the effort to reduce cellular data consumption, I put some monitoring code to keep track the amount of data usage at the TCP layer. ...
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7answers
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Why does DHCP use UDP and not TCP?

DHCP uses UDP as its transport protocol. DHCP messages that a client sends to a server are sent to well-known port 67 (UDP—Bootstrap Protocol and DHCP). DHCP Messages  that a server sends to a client ...
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1answer
35 views

Transport layer segmentation and Ip layer fragmentation [duplicate]

From the OSI Model's point of view: If we already have Ip fragmentation which happen due to the network limitation, why the transport layer provides the segmentation mechanism via TCP protocol? why ...
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1answer
56 views

TCP flow control active waiting

To perform flow control between a sender and a receiver during a TCP connection, the receiver includes in each packet to the sender, the size of available space ‘rwnd’ in its receiving buffer. This is ...
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2answers
437 views

Is a datagram from an upper network layer converted 1:1 to one of the lower layer?

I know datagrams from upper layers are converted to those of lower layers by adding metadata, but I cannot seem to find this information anywhere. Which one of the below is correct? A single TCP ...
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26 views

Why TCP is not in layer 5? [duplicate]

I read that TCP is in layer 4. But i also read that to send data with TCP i have to establish a session (in the handshaking phase). Does this mean that if we work only up to layer 4 TCP is useless (...
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1answer
35 views

TCP implementation [closed]

Can one speed up TCP transmission of packets if the no.of bits in sequence field and no. Of bits in acknowledgement field are reduced ? If yes , then how much time is saved? Mathematical equations for ...
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1answer
42 views

Is it possible for two TCP connections to have the same SEQ/ACK number?

Say we have many TCP connections established between various ports. Is it possible for two of these connections on different ports (eg. 50000 -> 80, 40000 -> 80) to have identical SEQ or ACK numbers?
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1answer
58 views

TCP handshake immediately RST [closed]

I'm trying to set up a modbus TCP connection on port 502 but get a RST packet immediatly. So the TCP connection handshake doesn't even succeed. This is done on a windows machine on an ESX server. The ...
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1answer
26 views

Does network layer provide connection oriented service

I know that in TCP/IP model the data link layer provides connection less service. While reading IPv6 Header. 'The flow label is used for connection oriented servie'. How does TCP/IP model provide ...
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1answer
27 views

What is the time of the first RTO in the TCP protocol without knowing the RTT?

I know that 3 way handshake is used. But, the first time a connection is established and there is no RTT data, what is the expected time before sending another packet? How does the client know how ...
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2answers
320 views

Why are session states synchronized with high availability?

Like my title says, why are session states synchronized between peers in most HA protocols? I assume TCP states like Esablished, Invalid, New and Related are synchronized, but I don't get why you want ...
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1answer
40 views

Packet analyze on router does not match client and server

thank you for your time. My (virtual) network has 3 objects : a client, a server and a router between them. I'm sniffing the traffic on the 3 machine with the command tcpdump -i any -s 0 -w [path] ...
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2answers
65 views

Sequence numbers of segments in three way handshakes of TCP connection establishment or termination

I was trying to understand TCP connection establishment and termination steps from Forouzan's book. In third step of three way handshake of connection establishment, it says following The client ...
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1answer
52 views

Is TCP aware of MAC adress

lets say I would like to make connection between client and server on port 80. Is 3 way handshake aware of server MAC address? I mean: client send SYN data packet to specific IP:port and MAC. In ...
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1answer
28 views

How retransmission timer is set/reset in TCP after receiving ACK?

I come across following, while reading TCP from Forouzan's book: We can define the following rules for the retransmission timer: When TCP sends the segment in front of the sending queue, it ...
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1answer
48 views

What layers of the TCP/IP model does an SDN involve?

New to Software-Defined Networks. I know that an SDN involves an Application plane, a control plane and infrastructure plane. By definition, I know that the application plane is in the Application ...
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1answer
50 views

Understanding TCP's slow start exponential increase congestion control policy

I was learning TCP slow-start exponential increase congestion control mechanism from Forouzan's book. It says following: The size of congestion window (cwnd) starts with one maximum segment size (...
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1answer
19 views

Question on windowing and determing connection speed

Hi i'm just learning computer networks and i have learned about windowing in tcp And my question is does we determine connection speed using windowing? I mean computer know the number of packets and ...
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1answer
108 views

When TCP sender window shrinks?

I was learning TCP from Forouzan's book. It explains sender side window as follows: In that it defines size of receiver window as follows: rwnd = receiver buffer size - number of bytes waiting to ...
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1answer
86 views

ports and security

I'm thinking about how the "port" operates for the network connections and tried reading the CCNA cert. guide to understand the details, however, I need to clarify doubts: does occupying all the TCP/...
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1answer
39 views

Finding MSS for a remote connection that uses tunnelling

I'm working on a codebase where we're trying to test network health by verifying if we can ping the remote site having payload = MSS without any packet fragmentation (using -df flag). Typically, for ...
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2answers
62 views

Not a four-way handshake in Cisco Packet Tracer?

TCP connection termination is performed by the four-way handshake, as shown below (the image is taken from here). I tried to verify it on Cisco Packet Tracer. With the following topology, I captured ...
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Will Eifel detection algorithm conflict PAWS?

From The Eifel Detection Algorithm for TCP: Given that timestamps are enabled for a connection, a TCP sender always stores the timestamp of the retransmit sent in the beginning of loss ...
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2answers
76 views

Why the three-way handshake use so short time accomplish it?

I use the Wireshark captured the packages: in there you see the number 1594-1596, the three-way hankshake only use 0.0002s(0.2ms) it complete it. but when I in the server(103.215.9.27) ping the ...
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1answer
73 views

what is the definition of out degree and in degree in computer networks?

in wikipedia we have a good definition for in degree and out degree in a graph: " The degree of a node is the number of connections or edges the node has to other nodes. in-degree is the number of ...
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2answers
262 views

Why the TCP client haven't receive the ACK response, it send the FIN package?

I use the WireShark captured the TCP connect. you see the three-way handshake(1-3) and the four-way handshake(5-8): But, from the frame list, I have a question about TCP. You know the TCP should ...
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1answer
55 views

Why the seq number set to random, there will be safer in TCP connect?

From the TCP document I have read this: First, client sends a TCP packet with_ SYN=1, ACK=0 and ISN(Sequence Number)= 5000_. Do not forget, sequence number is random and it could be between 0 to 4,...
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1answer
82 views

is there any limit/role for `syn` initial number and `seq` number of TCP three-way handshake?

We know the TCP three-way handshake, I want to know is there any limit/role for syn initial number and seq number? I hear about the number set random can protect server, who can help talk about this?
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46 views

Is it possible to re-transmit only the last packet at TCP flow?

I try to understand the TCP behavior, especially re-transmission. I did a small experiment and find the curious thing. The only last packet is re-transmitted. Why do this happen? I think if the ...
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1answer
42 views

What's the hook and double hook meaning in wireshark?

What's the hook and double hook meaning in wireshark? you see the two snapshots up there, when I select #7 the #6 will be hooked. when I select the #8, the #5 will be double hooked. What's the ...
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1answer
57 views

The reason a TCP connection generate retransmission

My question is why a TCP flow make a re-transmission when a network has enough link bandwidth. For finding a cause, I used a wireshark. I got the below captured at a host side (10.0.0.1) 85968 47....
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1answer
75 views

If you're behind a firewall and all the ports are blocked, how is your browser able to access the internet?

I'm behind a router and I'm able to run game servers on my home computer after forwarding ports or using the DMZ feature on the router. However, I still don't understand the underlying technology as ...
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1answer
53 views

TCP cwnd is increasing when congestion occur

I am a newbie network engineer. I did a small experiment with iperf3. But I run into a small problem. (1) My question. I think TCP flow do not act properly despite of its congestion control. The ...
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1answer
52 views

How TCP find the correct application?

I am learning how TCP and application communicate with each other. I am not sure if my understanding is correct, I will use below example to illustrate my understanding and want to ask some questions. ...
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1answer
37 views

What technique is my ISP using to censor web traffic? [closed]

BBC news is censored in the country where I live. Out of interest I decided to briefly look at how this is done. First of all they apparently MITM DNS - if I look up BBC domains on Google's 8.8.8.8 I ...
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2answers
172 views

Why do transport layer do data chunking. If there is fragmentation in Network Layer

I just curiously wanted to know about the question regarding L4, L3 Data Chunks, IP Fragmentation : Data chunking happened at Layer 4(Transport, TCP), and Fragmentation at Layer 3(Network, ipv4) ...
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1answer
119 views

How can I accomplish VPN across Dual Wan connections?

How can I accomplish VPN across Dual Wan connections in a optimal way? Idea is to make: Site to site VPN. Make single connection inside the VPN to use full bandwidth of both wan connections using (...
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1answer
291 views

TCP connections hang during handshake [closed]

For the last few days, connections originating behind my LAN's NAT have been having issues completing the TCP handshake (i.e. web pages only load after hitting F5 a few times, network applications ...
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3answers
1k views

Sending less data than the TCP buffer could take

The accepted answer of this question explains: When you send data, your TCP buffers it. So if you send a character it won't send it immediately but wait to see if you've got more. But what if I ...
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1answer
47 views

Juniper EX Switch sending TCP reset on SSH connection randomly

So as stated in Title I'm observing that one of our switch randomly send RESET flag in TCP and ends the ssh connection in the middle and sends and Window size of 0 as well. Randomly it refuses to ...
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1answer
59 views

Does HTTP proxy sends its own TCP packets or bypasses clients packets?

Need help to understand what's happening on TCP level when http proxy is used. When client wants to open a website through a proxy, first connection is established between client and proxy. Then ...
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1answer
113 views

Sending TCP packet to the other device without connection

I think the sending packet to other device works like the following. 1. The server device listens with port. for example 80 2. The client connects to the server devices. for example, the port of ...
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7answers
6k views

Why isn't UDP with reliability (implemented at Application layer) a substitute of TCP?

TCP provides reliability at transport layer while UDP does not. So, UDP is fast. But, a protocol at application layer can implement reliable mechanism while using UDP. In this sense, why isn't UDP ...
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1answer
69 views

TCP sequence numbers in Actual Transmission vs. in Wireshark Capture

Whenever, we do a wireshark capture and Follow--> TCP Stream, we see the sequence numbers as fixed values. In reality, if this were the case, the intruder can easily predict the transmission patterns....
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1answer
74 views

Response time of TCP congestion control

I would like to know about the overall latency of the TCP congestion control for adapting to varying network conditions. Specifically, my questions are: How fast can the system react after a change ...
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2answers
351 views

How to measure max bandwidth with Wireshark?

I'm trying to measure the max bandwidth usage of my LAN with Wireshark. I´ve done several packet captures but I don't know how to obtain the max bandwidth usage. Any Idea? Thank you in advance