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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Expected delays accessing server via IP locally via DNS locally and globally [on hold]

I would like to know the expected delays (if any) in accessing a server in the same network and via the internet. Hypothetically I am on the local network and my IP is 10.16.140.74 I access a ...
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19 views

Why are PTO and RTO high compared to early retransmit time?

The detection and retransmission of a probably lost packet via early retransmit or RACK takes roughly 1*RTT, at least in high latency environments. In case of a tail loss, a probe Timeout (PTO) will ...
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15 views

Port Forwarding testing [on hold]

I am working on a task where i had to disable port forwarding. For this, I turned AllowTcpForwarding and X11Forwarding to No. What i am looking to do now is to do some sort of Port Forwarding test to ...
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10 views

A tcp based client-server system using ns3 [on hold]

I am completely new to ns3. All the tutorials that are given in the repo mainly consist of echo servers where they are sending a packet of specific size and receiving the echo. I want to design a real ...
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2answers
309 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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18 views

Modbus URI scheme [closed]

Is there a standardized URI scheme for the Modbus TCP protocol to access ressources? It seems to me that it does not exist, can somebody explain to me why not? I found a document, which uses the ...
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1answer
38 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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19 views

Very strange: Where in the network stack is linuxmint.com blocked system wide [closed]

I am using windows. I can access it from a bridged VM on the same device with the same DNS configuration. It continues to be blocked even with third party upstream DNS providers and local revolvers, ...
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2answers
34 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
39 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
23 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
33 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
41 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
18 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
73 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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92 views

why iperf3 UDP throughput is lower than the TCP throughput?

I'm running an iperf3 throughput test from my PC to another one, going through a router. I've tried the same configuration for TCP traffic and for UDP traffic. However, for UDP traffic, I get worse ...
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2answers
50 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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38 views

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
74 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
61 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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142 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
52 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
75 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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1answer
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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11 views

Can a UDP service and TCP service use one port? [duplicate]

When we open a UDP or TCP connection, there will start a port in server. there I have a question, can a UDP service and TCP service use a same port?
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1answer
39 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
55 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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24 views

When read() rates is slower than arrived TCP packet rate [closed]

I have a question about TCP behavior. At receiver side, when the system call read() processing is slower than the TCP packets arrived rate, Does the packet loss and re-transmission occur? I know ...
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1answer
65 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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49 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
49 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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51 views

Rebuild video stream of TCP packages

I would like to rebuild a live stream that I captured via WireShark. I receive several decrypted TCP packages but am not able to export them as mp4 file or something similar. Here is an illustration ...
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1answer
32 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
76 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
113 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
285 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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26 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
47 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
90 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
63 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
69 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
165 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
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1answer
65 views

Why the Ack number is bigger than the last Seq number?

Why the Ack number is bigger than the last Seq number? you see the Ack response for each two TCP packages. but there I have a question, you see the Ack response for Seq=19997, Seq=22893 and Seq=...
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1answer
157 views

Dropping packets between router and firewall without firewall rule

I have a user that is trying to access his company network resources on his home network. He is able to access SMB shares and other resources, but he is unable to access their AS400 on any computer in ...
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1answer
56 views

Wireshark captures TCP packet with no flag [closed]

In our network, I captured a TCP packet by Wireshark that has no flag set. What's that mean? Is it normal?
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95 views

Behaviour of TCP SACK

I will ask the question based on the following scenario. Assume I have to send 10 packets using TCP using a window size of 5. I send 1, 2 and receive ACK for them, I send 3 and the ACK is lost, I send ...
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1answer
68 views

Why server cannot send data in TCP three-way handshaking?

In the three-way handshaking, only from the ACK packet we can send data. Why cannot the server send data with SYN-ACK packet? I understated why a client cannot send data to a server (preventing, for ...
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3answers
172 views

What's the use of an acknowledgement number without the ACK flag set?

Isn't it redundant if the ACK flag in the header isn't also on? Do you ever mix an acknowledgement with a normal message - send data and acknowledge a message in the same TCP segment? I feel like ...