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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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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
43 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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1answer
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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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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
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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
266 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
36 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
125 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
95 views

Can anyone Explain me difference Between PSH and URG flag 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 ...
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4answers
138 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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0answers
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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
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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
56 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
76 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
50 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
19 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
150 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
164 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
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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
44 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
81 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 ...
3
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1answer
315 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
232 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
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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
370 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 ...
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2answers
46 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
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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
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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
3k 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
94 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
302 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
59 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
349 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
105 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
184 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
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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
2k 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
996 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
1k 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
164 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 ...
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1answer
551 views

Relationship between TCP window size and TCP congestion control

Am I correct that TCP receive window(which is a send window for the sender) has nothing to do with TCP CUBIC congestion control? TCP receive window is solely a property of TCP flow control?
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3answers
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How is tcp/ip implemented

Well, first of all I am new to networking. And I have studied the layered structure of tcp/ip protocol stack. I know that the layered structure is an abstract model, but I didn't know how the ...
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1answer
492 views

How do data packets travel without merging?

I have been very interested in networking for quite a while, and I have been wondering this question. I've been thinking about this in complete binary, meaning how does a 0 of a data packet not get ...
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1answer
186 views

Does 1-byte transmission for probe segment operate based on Timeout?

I wonder what ACK number would be if the receive buffer of receiver side is full. For example, Consider a case that sender transmits a segment whose SEQ is 800, and 100 bytes size. Because the receive ...
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1answer
94 views

Can you vlan tag and assign a priorty (0-7) to SCP traffic

My question is in relation to the file transfer protocol SCP. I have a local time sensitive network built. In time sensitive network you can give priority to traffic by vlan tagging and assigning ...
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4answers
427 views

Port Numbers related doubt

Assume we have two browsers (Chrome and Firefox) running simultaneously, and both are requesting a web page. Lets assume Chrome is requesting www.facebook.com, and Firefox is requesting www.youtube....
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1answer
55 views

TCP Vegas: formula for expected number of backlogged packets

While reading Issues in TCP Vegas by Richard J. La, Jean Walrand and Venkat Anantharam (available online here), I stumbled across the following sentence (Part 3 - Rerouting, page 4): When the ...