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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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6 votes
2 answers
2k 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) ...
23 votes
2 answers
23k views

How multiple client connections are made to single web server?

Actually I am learning Computer Networks and while at it, I am confused in how a web server maintains multiple connections? Simply to state, I learned trough some googling is that sockets handles a ...
0 votes
0 answers
12 views

Flapping RTR Session between RPKI Server and IOS-XR Router [closed]

We are trying to integrate our IOS-XR routers to an RPKI server. The RTR has been established via TCP/3323 but we have noticed that the RTR session is flapping between the router and RPKI server. As ...
3 votes
3 answers
421 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, ...
5 votes
2 answers
750 views

Why is MSS important? Why can't we just rely on the MTU?

Note: I understand both what MTU and MSS do so I am not asking about their function here. I understand that when a TCP connection is being established, the MSS is exchanged and it dictates the maximum ...
0 votes
1 answer
36 views

Where is netmask information stored?

I have some practice with networks, but not much theory. I saw in this question that netmask is not stored in the TCP/IP packet. However, from my experience if I: connect machine A to port 1 of ...
0 votes
0 answers
10 views

The TCP connection is always reset while transmitting a 6M file [closed]

I have a web server, which allows user to upload or download files through HTTP requests. Internet Internet loopback interface LAN ...
8 votes
5 answers
6k views

Is rerouting possible in UDP?

So I am trying to understand routing for TCP and UDP segments. I have a couple of things that I am confused about: In TCP, is there any specification on how many packets would be dropped before a ...
0 votes
1 answer
36 views

Can an L4 Load Balancer shift an existing SCTP/TCP Connection from One Backend Server to another without requiring client to make a new Connection?

I'm currently working on a network setup that uses an L4 load balancer to manage traffic for our services. The L4 load balancer effectively distributes new client connections to various backend ...
2 votes
1 answer
546 views

Message formatting and encapsulation

I've gotten confused when reading about encapsulation and the OSI and TCP/IP models. I first read about message formatting and encapsulation and the diagram I read showed: Destination | Source and ...
1 vote
1 answer
56 views

What happens if the first segment after a 3-way handshake in a TCP connection is dropped

If I have a scenario with two hosts. Host A and Host B. Let's say that Host A initiates a TCP connection to host B. Let's say a connection has been established after a 3-way handshake. What happens if ...
1 vote
1 answer
54 views

Acknowledgment numbers in Wireshark do not match sequence numbers

Recently, I conducted an experiment involving uploading a file to a server. I noticed that the acknowledgment numbers I received did not align with the sequence numbers. Please refer to the attached ...
3 votes
2 answers
2k views

Why don't tcp sequence number start from 0?

In TCP, one purpose of 3-way-handshake is to exchange initial sequence number for both sides. So why not use 0 instead, and the exchange is not necessary. That is to say, sequence numbers can be ...
1 vote
4 answers
1k views

Why the combination of "TCP/IP" is more popular than "UDP/IP" [closed]

According to 7 Layers of the OSI Model, IP is located at layer 3 (Network), while TCP and UDP are located on layer 4 (Transport). Just for the sake of curiosity, why the combination of "TCP/IP" term ...
2 votes
1 answer
2k views

How does wireshark calculate the TCP length when there is no header indiciating such?

In wireshark, you have this field: [TCP Segment Len: 1380] # How is this calculated? My assumption is using the IP headers plus TCP's. TCP Segment Len = IP Total Length - IHL - TCP Header Length In ...
2 votes
2 answers
98 views

Can TCP seq number increment after sending a FIN?

I have an embedded device connecting to a server (on AWS Application ELB if that matters). Both the server and the client are instructed to close the connection after one request. I noticed that the ...
2 votes
1 answer
401 views

How can I configure a Cisco router 4300 to allow internal server ip:80 to be accessed on public ip:4500

I have an internal web server on port 80. I need help commands maybe to configure port forwarding to access the server on my private network from a public IP Current running config interface ...
0 votes
1 answer
85 views

In wireshark, why following a TCP or UDP stream does not remove ICMP packets?

In Wireshark, when I follow a TCP or UDP stream using right click -> Follow -> UDP Stream, if there are some ICMP packets from same endpoints, wireshark will keep them in the stream. Why? Since ...
1 vote
2 answers
5k views

How are websites accessed without port numbers?

I am confused on how requests to websites are received. If I type in 172.217.5.110 to my browser, google.com sends me its home page. I didn't have to specify the port number. How does that work? I ...
0 votes
0 answers
14 views

Clarification of relation between IPv6 and TCP [duplicate]

I thought IPv6 and TCP could be used independently, but IP does not need TCP at all, whereas TCP usually needs IP to function. Is my understanding correct? Does IPv6 need TCP to function? Looking at ...
4 votes
4 answers
1k views

TCP/IP and data cut

I would like to clarify my understand about TCP/IP model and packet cutting. I think it's done by layer 3 (Transport, eg. TCP) but I'm note sure about layer 2 (Network, eg. IP) or even layer 1 (...
0 votes
2 answers
85 views

How to connect TCP server behind NAT

I need to establish TCP connection with a server located behind the NAT. The simple solution is to reverse the connection and ask the server to connect to the client, but then I am unable to use ...
0 votes
1 answer
650 views

What will be the sequence number consumed by FIN flag? [duplicate]

In the connection termination phase, suppose the FIN segment from the client-side contains data ranging from sequence no 100 to 200, So will the ACK no from the server start from 201 or 202? Will the ...
1 vote
2 answers
120 views

How to calculate sampleRTT?

I'm working on a TCP implementation with UDP socket in C, and I'm trying to make the timeout variable with this algorithm estimatedRTT = (1-a)*EstimatedRTT + alpha*SampleRTT devRTT = (1-beta)*devRTT + ...
0 votes
1 answer
122 views

Why is this RST during handshake [closed]

This finally turns out to be a Linux kernel bug which is not fixed yet by 2023/12/18. (See https://lore.kernel.org/lkml/[email protected]) ---------------------------...
80 votes
5 answers
525k views

Ping port number?

Yesterday an interviewer asked me what the port number for ping is and which protocol ping uses: TCP or UDP. After the interview, I searched on the Internet and found different results: someone says ...
0 votes
0 answers
75 views

End to end delay over N link including the (simplified) propagation delay

It is well know (see this question) and easily verifiable that end-to-end delay in case of trasmission of P packets of size L over N equal links (same transmission rate R) with zero propagation delay ...
1 vote
1 answer
51 views

TCP Multiple Segment Acknolegdement

Let's take example where in the example i will use the Independent acknowledgment. Host A has send segment 1,2,3 to the host B, after host b receive each segment it will send a Acknolegdement for each ...
0 votes
1 answer
94 views

TCP Duplicate Acknowledgement

Host A and Host B has establish the connection, Host A will send a segment 1,2,3,4,5,6 but segment number 2 and 5 is lost. Then the receiver will sending an duplicate ACK to sender, so whenever sender ...
0 votes
1 answer
57 views

Reset Connection With RST Flag TCP

When a connection has been established between Host A and Host b, Then there is data exchange between host A and host b,Let's say host A already has 3 segments, segments 1 and 2 have been sent and ...
1 vote
1 answer
35 views

TCP Header Data Field

In TCP header there was a field called a data field which stores data, but does this field store the IPv4 header + datagram or just the datagram?
4 votes
2 answers
375 views

TCP MSS - Dynamic Adjustment

I've seen most of TCP flows having DF bit set. So, can any additional overheads like VXLAN cause TCP packet to be dropped (since DF bit set)? How will the TCP MSS be adjusted dynamically (in absence ...
12 votes
4 answers
44k views

How to know whether a protocol uses TCP or UDP

Well I know that might sound a stupid question and I believe that the most proper answer will be like I will be able to tell as my experience builds up and I learn more and more about the protocols. ...
0 votes
1 answer
61 views

What happens when the sender sends more data then the advertised window by the receiver?

I am relatively new to networking. I am doubting what happens when the sender sends more data than the advertised window by the receiver. I mean that the receiver advertises the window size based of ...
0 votes
0 answers
48 views

TCP blocked until the acknowledgment received

I am currently facing an issue in my application where the TCP messages seem to be blocked until an acknowledgment received. Specifically, the subsequent messages wait for the acknowledgment of the ...
0 votes
1 answer
55 views

Why MTU setting change not showing any meaning change in file transfer via tcp?

I performed a test in which I transferred a file of 1GB by opening a tcp port on destination server with MTU 1000. then I tried to change the MTU from 1000 to 9000 and the total time duration of 1GB ...
0 votes
1 answer
465 views

Wireshark filter for specific SYN packet which never received a SYN/ACK

Is there a way in wireshark to find out a single SYN that does not get answered by SYN/ACK?
7 votes
7 answers
3k views

Redundant IP link aggregation for failover operation without route failure detection

I am looking for a technology to achieve TCP connection fault tolerance with the help of two links between hosts and without time delays for route failure detection. Something like this: ...
0 votes
2 answers
74 views

Why is congestion collapse from undelivered packets not possible when there's 1 congested link?

rfc 2914 says this: The avoidance of congestion collapse from undelivered packets requires that flows avoid a scenario of a high sending rate, multiple congested links, and a persistent high packet ...
1 vote
3 answers
2k 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 ...
0 votes
1 answer
607 views

How to determine which TCP payloads should be combined to form a complete PDU?

I understand that the TCP itself provides a byte stream connection, but has no idea nor does it care what its payload is and how it is segmented to fit into individual packets that travel on the wire. ...
0 votes
1 answer
40 views

Are TCP connections within a host aware of one another? [closed]

I was wondering how a typical TCP/IP stack of a Windows or a Linux machine works in terms of congestion control. So, are active TCP connections within the OS aware of one another? I mean, the actual ...
11 votes
2 answers
3k views

Why does FTP passive mode use a range of ephemeral ports as opposed to a single well known port? [closed]

In FTP passive mode, I read that the server sends a random port number to the client where it can establish a data channel. Then client establishes a data channel from its random port number to this ...
0 votes
1 answer
314 views

How does cumulative acknowledgement mechanism allows for straight-forward duplicate detection in case of retransmission?

I'm reading the RFC 793. https://www.ietf.org/rfc/rfc793.txt The acknowledgment mechanism employed is cumulative so that an acknowledgment of sequence number X indicates that all octets up to but ...
2 votes
3 answers
2k 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 ...
0 votes
1 answer
392 views

What is the maximum size of an application-layer message for UDP?

TCP is capable of segmentation, i.e. even if the application layer creates an arbitrarily large message, the transport layer under TCP will split it into segments. Now, as per this answer, UDP doesn't ...
0 votes
2 answers
84 views

How does leaving a TCP connection half-open makes SYN and SYN+ACK stealth and absent from the logs?

I was studying about TCP SYN (stealth) scan which involves carrying out port scan while avoiding detection. I also read that it is similar to TCP connect scan except that the last ACK packet is ...
25 votes
4 answers
12k views

Does physical distance affect download speed?

I just had an argument with a colleague of mine and thought I'd just reach out to the experts on this. Here's the scenario. We were using a website that measures your connection's speed. We tested ...
13 votes
1 answer
3k views

Why in TCP the first data packet is sent with "sequence number = initial sequence number + 1" instead of "sequence number = initial sequence number"?

In the 3-way handshake, the initial sequence number of both endpoints of the TCP connection is synchronized. Here is an example: Endpoint A randomly generates an initial sequence number: 123. ...
13 votes
3 answers
37k views

Wifi TCP iperf throughput: 1 stream vs multiple streams?

In a WLAN iperf TCP throughput test, multiple parallel streams will give me higher throughput than 1 stream. I tried increasing the TCP window size, but I still cannot achieve the max throughput with ...

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