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Questions tagged [transport-protocol]

For questions about or in relation to the transport protocol or OSI layer 4. For instance the best-known transport protocol of TCP/IP is the Transmission Control Protocol (TCP).

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2answers
33 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
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
79 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
41 views

How is port 80 associated with application port?

I'm new to networking, just a question on port numbers. We know that port 80 is for HTTP. But if I want to access a web application whose web server handles http requests, normally I type below url ...
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1answer
30 views

What's the word of a Transmission Control Protocol port in the Wireshark captured package?

What's the meaning of the dict there? why the port have the paraphrase? you see the Destination port 39578 (39578) do not have.
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1answer
33 views

How does browser decide which destination port to use?

Suppose I have a Vanilla machine and this is the first time I am connecting it to Internet. There is no Cache at any level. I access a website through browser by typing example.com (no http//: or ...
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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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2answers
45 views

Overload PAT Question

Learning details of NAT PAT. I understand basics wherein the PAT router incorporates a source port to ID the private address computer communicating out on the public address, enabling the public ...
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1answer
67 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
168 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 ...
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6answers
4k views

Could IPv6 make NAT / port numbers redundant?

From what I can tell, each process could get its own IP address, with loads of IP's to spare. What would the drawbacks be? Essentially, your host would become a router and each process is a host (in ...
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0answers
45 views

Why do I observe a 4-way TCP handshake instead of an expected 3-way when establishing a connection? [duplicate]

I'm doing a simple HTTP GET query on a localhost from curl to a local webserver. After I did a tcpdump I noticed these packets to be sent each time a request is done: 11:11:27.537300 IP 127.0.0.1....
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1answer
334 views

TCP Three Way Handshake?

I have the following query about the tcp handshake. To establish a connection the server must send a packet with SYN flag to 1 Then the server replies with a SYN,ACK flag to 1 , and afterwards the ...
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1answer
47 views

Why does TCP need segments if the network layer automatically breaks things up into fragments?

I'm trying to better understand the difference between IP fragments and TCP segments (https://www.shubhsblog.com/tech/difference-ip-fragmentation-tcp-segmentation.html) and there's one thing I'm not ...
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2answers
136 views

If an old FIN is delivered, will TCP terminate the new connection?

Two programs use a TCP connection (3-way handshake) to open, communicate, terminate the connection and open a new connection. If a FIN message sent to shut down the first connection is duplicated and ...
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2answers
1k views

Can anyone explain to me the difference between the PSH and URG flags in TCP segment?

According to me when PSH flag is set, it indicates that data will have to be sent immediately to the wire and on receiving side the data has to be pushed to the application immediately. When URG flag ...
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4answers
175 views

WAN encapsulation

I am having some trouble understanding why does a WAN link need encapsulation, such as MPLS or frame relay? Is it merely to encrypt the info from one LAN to another LAN across the internet?
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28 views

what protocols does EAP AKA use?

can someone please explain me what protocols does EAP AKA use with respect to the OSI model? (for example what protocol it uses in data link layer and what protocol in transport layer)
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1answer
65 views

Is an RST only segment ever legitimate?

Is a TCP segment with RST but no ACK ever legitimately encountered today? While some kernels emit such an RST when a SYN segment is sent "illegitimately" from themselves (e.g., nmap half-syn, scapy, ...
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Does Selective Repeat (SR) ARQ protocol, retransmit all currently unacknowledged segments in the window, or just the base?

I've read several conflicting resources, from text books and different slides, where some even seem to contradict themselves through examples. When an SR ARQ packet is lost, and the timer expires is ...
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1answer
91 views

TCP - correlation between ACKs and receive window

EDIT: I think i get it now. So a simple sliding window mechanism basically assumes the correctly received data is processed immediately. Therefore an acknowledgement implies the data was received AND ...
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1answer
158 views

TCP or UDP for Stop & Wait / Go Back N

I'm creating server/client classes for "Stop & Wait" and "Go Back N" (variant of sliding window) protocols, though I'm unsure on whether I should pursue TCP or UDP. From my current understanding I ...
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1answer
52 views

Of what layer is socket a concept?

In network layer, IP address is a concept. In transport layer, port is a concept. Is socket a concept of transport layer? If not, what is the corresponding concept to socket in transport layer? Of ...
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1answer
20 views

Do different IP addresses correspond to nonoverlapping sets of ports?

If a network interface has two different IP addresses 1 and 2 assigned to it. and the port numbers in (IP address 1, port number) and (IP address 2, port number) are the same number, does it mean the ...
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1answer
371 views

How do TCP connections work?

The TCP establishes a connection between the source and the destination. My questions are: What do we mean by end-to-end communication? What is the role of that connection?Couldn't reliability be ...
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2answers
323 views

How does a TCP segment fit into a smaller IP packet?

The IP protocol can handle fragmentation and it includes the fragmentation offset and identifier. I know this comes into play when your IP packet is too big for some specific network or link where the ...
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1answer
158 views

How does the transport layer tell UDP apart from TCP?

So I'm reading Computer Networking: A top down approach (where these images are from) and I was looking at the Transport layer. A generic segment in the transport layer has a pretty simple structure: ...
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1answer
48 views

How MPTCP closed connection?

how MPTCP connection with more than one subflow closed? what would happen to MPTCP connection if a client decide to close one of the subflows? it would be very kind of you if you explain it step by ...
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1answer
114 views

Understanding acknowledgement mechanism in sliding window protocol

I came across following problem: Node A sends packets to B through router R. The link A-R is instantaneous , but the R->B link transmits only 1 packet each second , one at a time . Assume A sends ...
11
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3answers
2k views

acknowledgment by TCP does not guarantee that the data has been delivered

In RFC 793 there is a part about the acknowledgment of TCP segments: When the TCP transmits a segment containing data, it puts a copy on a retransmission queue and starts a timer; when the ...
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1answer
386 views

How can a UDP Client and a packet sniffer run on the same machine?

In my understanding, if you have a UDP socket client that is bound to a particular port, then a second UDP client on the same machine can't bind to the same port. If this is the case, then how can a ...
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2answers
248 views

tcp connection and stream flow question

Could anyone explain the main principe of tcp flow when making a session ? I have take a tcp dump when i'm trying to browse a site. when I analyse the packet by wireshark, i have found many Three way ...
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1answer
30 views

Is it possible to implement virtual network based on MAC in IP instead of MAC in UDP?

We know that flannel use MAC in UDP to create a overlay network. My question is: UDP header only provides an extra port number fields, let's suppose that one physical machine only run one flanneld ...
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1answer
31 views

Question about output of 'lsof -i' and UDP being connectionless

I'v got a simple setup: Server (IP 10.0.0.33) listening on port 7770 using the command: $ netcat -lup 7770 And a client (IP 10.0.0.2) that communicates with the server using: $ nc -u 10.0.0.33 ...
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2answers
481 views

How does the Transport Layer construct the Pseudo-Header for TCP checksum?

THE TCP Psuedo Header needs sender and destination IP Address and protocol type. All of this informations is present in the network layer/IP header. Since the transport layer cannot access the data ...
3
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2answers
52 views

How could a response be sent to the requestor without requestor's address?

I'm reading this talking about the differences between two fire-and-forget message (for example, under UDP) and a request-response communication (for example, under TCP). I came across this: The ...
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0answers
58 views

Processing received SACK information in case of reordering

I would like to understand how TCP receiver in established state should treat SACK information of out-of-order and fully within receive window segments, where rcv_nxt < seq_no < rvc_nxt + ...
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4answers
3k views

Why is a TCP Socket identified by a 4 tuple?

Newbie to networking here. I'm reading the Computer Networking (3rd edition) book, and in section 3.2 they are discussing multiplexing / demultiplexing for both UDP and TCP. In the UDP protocol, a ...
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1answer
4k views

How can a TCP window size be allowed to be larger than the maximum size of an ethernet packet?

I know that TCP window sizes can be scaled to over 64KB, but looking at an ethernet packet datagram, such as this one: it looks like a layer 2 packet is limited in size to be much smaller than that. ...
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1answer
122 views

Questions about TCP packets

I am currently in college learning about networks, and I just wanted to make sure that I understood part of the TCP correctly. The question is "What does TCP use to reassemble packets in the correct ...
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1answer
560 views

Session ID vs Port number

How does the session ID differ from the port number? at the Application layer, Port Number Identifies the service, same for session layer. right? and these port numbers are assigned at Transport layer....
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1answer
61 views

How TCP and firewall handle security?

I'm a newbie in networking, still don't quite understand about security. Let's say a person A uses TCP to establish a TCP connection with a server. And there is a hacker B who is sniffing, so B ...
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1answer
467 views

Sender and Receiver timers in GBN, SR and TCP?

So basically for each of the GBN, SR and TCP's retransmission method, i have 2 question: 1.Is there a Timeout timer for EACH packet or one timeout timer for all of the packets? 2.Is there a ...
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1answer
150 views

Computer networking dwdm [closed]

Why do we use digital cross connects, which define permanent cross connect between source and destination in core network while the PSTN allocated circuits dynamically as both are types of circuit ...
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1answer
239 views

TCP close 2-way handshake with tcpdump package

Well, I got a pcap package that uses the tcpdump command. In this pcap, the TCP closes in 2-way handshake! Questions: In this picture, can anyone determine who initiated the signal to close the ...
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2answers
77 views

Why is ARQ (Automatic Repeat reQuest) named so?

I can't make sense of a naming for Automatic Repeat reQuest. The idea is that ARQ is a method for transmitting data without negative ACKs, so standard ARQ flow is: Sender sends a packet If sender ...
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2answers
3k views

Error control in Transport Layer vs Data Link Layer

I understand that under the TCP/IP Protocol Suite, error control, flow control and other such services are provided by both, the Transport Layer and the Data Link Layer. My doubt is specific to error ...
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2answers
1k views

TCP's three-way handshake and Denial of Service attack

Hi I'm a newbie in networking, still confused with the relationship between three-way handshake and Denial of Service attack. As we know that if the client does not send an ACK to complete the third ...
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2answers
2k views

TCP Fast Retransmit and duplicated acknowledgements Ask

Hi I read an Textbook(Computer Networking : a top-down approach / James F. Kurose, Keith W. Ross.) describes the process of TCP's Fast Retransmit, basically TCP retransmits the lost paclet when it ...
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2answers
274 views

Send TCP request to closed port, In which layer will the request be discarded

Client send TCP packet to server to a closed port, ie 80. In which layer will the sync packet be discarded? I guess for Client, the request will timeout, for server it should discard the request ...