Questions tagged [layer4]
For questions about OSI Layer 4 (transport layer).
158
questions
2
votes
1answer
601 views
Which one right, UDP has 508 or 512 bytes payload limits?
We know the size guarantees the datagram won't be fragmented in IPv4 is maximum 576 bytes. But the size when use UDP header 8 bytes and if we take UDP payload 512 bytes and choose maximum header size ...
0
votes
1answer
42 views
Why loss of first Syn + Ack from the server will not establish a connection? [duplicate]
In TCP 3-way handshake, 3 segments will be sent (SYN, SYN ACK, ACK). What if loss of syn+ack from the server will not establish a connection? What if the third segment(ACK) is lost? Is the sender ...
-2
votes
1answer
116 views
Why sender window or congestion window size becomes 2^n mss after nRTT in slow start mechanism?
I seen everywhere in slow start mechanism if initial sender size denoted by cwnd= 1mss , then after 1 RTT cwnd becomes = 2 mss, and after 2 RTT cwnd becomes = 4 mss and so on. My question is why ...
0
votes
1answer
75 views
Is really TCP takes 3*RTT time to make a connection?
TCP takes 3 RTT time I have read from one stack overflow answer to make a connection with server. We know that TCP takes triple (Syn, Syn/Ack, Ack) to make a connection by 3-way handshake with server....
0
votes
2answers
93 views
Why client will send a RESET when it is closed state?
Suppose I have an TCP state transition diagram. And assume that the last ACK is lost. Then, B will think that A did not receive the FIN and will retransmit the FIN. From B point of view this is the ...
-1
votes
1answer
80 views
Why the pseudo-header is not transmitted with the UDP datagram?
I have read from E. Comer - Internetworking with TCP/IP 4th edition that "The purpose of using a pseudo-header is to verify that the UDP datagram has reached its correct destination. The key to ...
0
votes
1answer
89 views
UDP checksum calculation for checksum results in the value zero
I read UDP checksum from Wikipedia that "If the checksum calculation results in the value zero (all 16 bits 0) it should be sent as the one's complement (all 1s) as a zero-value checksum ...
0
votes
1answer
80 views
Why UDP checksum is optional for IPv4?
We know that IPv4 header has checksum for header not for data .Therefore for checking data error we need checksum in transport layer. Suppose we're using UDP in layer 4. So if I remove the checksum ...
0
votes
1answer
48 views
How UDP checksum get IP address to make pseudo header in transport layer?
We know that UDP checksum's pseudo header contains the most important parts of the IP header, that is, source and destination address, protocol number and data length.
I hope that the concept of IP ...
1
vote
2answers
1k views
How is UDP used in multimedia system inspite of being connectionless
We know that UDP does not care about segment (packet) in-order and their arrival on the destination.Then how on YouTube or VoIP (skype) are we able to stream videos?
If a packets is lost (doesn't ...
1
vote
1answer
69 views
What happens to the packets in the sender buffer when "eventually a timeout would be reached" for a **delayed ACK** in a AIMD TCP connection?
In a AIMD TCP connection, What happens to the packets in the sender buffer when "eventually a timeout would be reached" for a delayed ACK for a specific packet at the sender side?
Suppose ...
0
votes
3answers
231 views
What would happen if TCP flow control is turned off hypothetically? [closed]
I understand that TCP flow control provides a way for the receiver to backpressure the sender. But what if we eliminated this from the protocol. Of course, the receiver would still ACK everything ...
1
vote
1answer
35 views
Nature of TCP Timeouts
Are timeouts in TCPs inherently part of sequence numbers, or is it an entirely different component of a TCP packet?
I understand that timeouts provide some level of reliabilty to a data stream, in ...
9
votes
5answers
2k views
Does the destination port change during TCP three-way handshake?
I'm learning networking programming in C and there is a question bothers me a lot, does the destination port change during TCP three-way handshake? Let's say I have a cilent application running on ...
1
vote
1answer
103 views
Does the first TCP FIN packet (active close) goes with just only FIN bit set?
Suppose we have established TCP connection. The active close process assumes the FIN packet been sent to trigger TCP connection closing.
But I can't figure out, is this first (active close) FIN packet ...
1
vote
1answer
69 views
Is there any other network protocol than tcp/udp that works with ports?
Do you know at least one protocol (any OSI layer) that, like tcp and udp, works with ports ?
Thank you
2
votes
2answers
186 views
Why is delayed segment prevention (TIME_WAIT) in TCP only done for one side?
One of the reasons for TIME_WAIT is to prevent old packets/duplicates, coming in late, to screw up subsequent connections on the same (src ip, src port, dst ip, dst port) quadruplet.
That makes sense, ...
44
votes
7answers
15k views
Does UDP do anything at all?
It's my understanding that TCP has logic for ensuring reliable communication, but UDP just naively sends information along the channel set up for it using IP and things in lower layers.
Does UDP ...
2
votes
2answers
414 views
What will happen if a server receives a duplicate SYN for an existing connection?
If a server receives a fresh SYN packet for a connection that is already established, what should it do?
I have already seen What will happen at server side if it received 2 SYN packet from the same ...
1
vote
2answers
213 views
Is this UDP diagram wrong?
I was just wondering if anyone can tell me why all UDP diagrams I have seen list a request from the server to the client as the first point of communication? Take a look at the following diagram for ...
-1
votes
2answers
371 views
What is the window size of TCP pipelined sending?
We know that instead of sending a packet and waiting a RTT then sending another (stop and wait), TCP uses pipelined sending as picture below shows:
So, my question is, what's the maximum number of ...
2
votes
1answer
230 views
Do both sides need to agree on MSS value?
By definition, The TCP Maximum Segment Size (MSS) is the maximum amount of data that a host is willing to accept in a single TCP/IPv4 datagram. And MSS is one of the parameters which is negotiated ...
0
votes
2answers
71 views
Diffie helman Agreement on Prime Number and Generator
So, to start DH, the two parties need to agree upon a prime number and Generator, correct? How do they do do that without someone listening in?
Where does the loop end/start?
Also, Does it matter if a ...
0
votes
1answer
937 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 ...
0
votes
1answer
675 views
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 ...
4
votes
1answer
197 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)...
1
vote
2answers
151 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 ...
1
vote
1answer
158 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 ...
1
vote
1answer
228 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 ...
5
votes
2answers
574 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 ...
1
vote
2answers
1k 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 ...
1
vote
1answer
73 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 ...
3
votes
1answer
2k 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 ...
1
vote
1answer
110 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/...
1
vote
1answer
76 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 ...
0
votes
0answers
21 views
how OSI and TCP/IP layers work? [duplicate]
I am really confused by how the layers these model work. I'm not asking about what are their functions. I read that transport layer provides end-to-end of all packet delivery, and networking also ...
0
votes
1answer
830 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 ...
2
votes
2answers
1k 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)
...
1
vote
1answer
803 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 ...
2
votes
3answers
1k 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 ...
1
vote
1answer
650 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 ...
2
votes
2answers
278 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 ...
9
votes
4answers
13k 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 ...
4
votes
1answer
279 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, ...
2
votes
1answer
479 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 ...
1
vote
1answer
85 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 ...
0
votes
1answer
52 views
Can a ACK or SEQ Number exceed a range and crash the NIC?
I was watching the TCP Stream out of pure curiosity of my FTP Server and saw that the ACK and SEQ number increases by one with each sequence being transmitted successfully. I am not sure, but ...
12
votes
3answers
3k 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
votes
1answer
455 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 ...
1
vote
1answer
137 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 ...
