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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TCP/IP, MTU, DHCP question [closed]

In the example network below, how would I determine the maximum number of IP addresses that can be allocated by the DHCP to user terminals in each of the subnets? Also, how long would it take to ...
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2answers
10k views

What's the difference between port number and protocol number?

Can someone explain it clearly. I know that port numbers are used by applications to differentiate which services you have requested, and routing protocols use protocol numbers in TCP header.
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What will happen if a sender use TCP and receiver uses UDP?

I am new to networking and was studying about TCP and UDP. One question came to my mind that what will happen if a sender uses TCP and receiver uses UDP for the communication.
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1answer
172 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 ...
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1answer
32 views

Latency between a churn and congestion event triggered in the TCP code

I am analyzing the time it takes between a churn occurring in the network (e.x. that causes packet drops or delays) and when the congestion event handling codes are triggered in the TCP kernel in the ...
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1answer
154 views

TCP Congestion Window

Looking at example of congestion window graph pasted below and wanted to confirm my understanding. Looking at the red bar would that be the timeout happening here due to ACK being lost? and the b1 ...
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1answer
37 views

Can UDP traffic be transmitted over TCP ports on OpenVpn to avoid the TCP meltdown

I understand the TCP meltdown problem is associated with overcompensation from errors and incorrect sequencing when arriving the the receiver end. OpenVpn connections are recommended to use the UDP ...
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2answers
187 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, ...
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1answer
411 views

Why SYN-RECEIVED sends reset on not acceptable ACK?

The tcp protocol actions on arriving segment vary. The set of choices includes: silently drop segment kill connection (i.e. enter CLOSED) send reset (and maybe kill connection) send dup/null ack (etc)...
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1answer
85 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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2answers
45 views

How can I use scapy to make a port appear open-device behind NAT?

This has been asked in stack overflow like 7 years back. I don't see the correct answer there. Is there any way to do this? While this packet keeps on being transmitting, doesn't the other end see the ...
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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 ...
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2answers
180 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
25 views

TCP payload error handling at the application layer [closed]

How are errors in the payload of TCP packets handled by the receiving application? The packet is received but for various reasons (including sending erroneous packets on purpose) the payload of the ...
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2answers
169 views

Slow SMB transfer rates with client direct to Cisco switch, normal when connected to a downstream Netgear switch

I have encountered a rather unusual problem that I'm having difficulty getting to the bottom of... Here is the configuration: SMB server ->(2x10Gb SFP+ LAG) Cisco SG500X-24 switch ->(1x10Gb SFP+)...
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3answers
13k views

Difference between IP checksum and TCP checksum

If an error on a packet occurs on a router, who does detect the error, IP checksum or TCP checksum? I have understood that the IPv4 checksum detects errors only inside the IP header and the TCP ...
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1answer
45 views

Difficulty in understanding the concept of "artificial inflate" and "deflate" in the fast recovery phase of TCP

I was going through the text Computer Networking- A Top-Down Approach by Kurose and Ross, there I found subtleties with the TCP congestion control FSM which is shown below: Mainly I am having ...
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1answer
6k views

Troubleshooting low Metro Ethernet TCP throughput

Background We rented a few layer 2 leased lines, i.e. you have one big pipe at the datacenter and the remote sites have smaller pipes. Inside the layer 2 network you can do whatever you like. Probably ...
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132 views

Is the TCP Reno Fast Recovery algorithm really linear?

I'm reading through Computer Networking, 8th Edition by Kurose & Ross, and I came upon this figure(Figure 3.52 pictured below), which graphs the operation of TCP Tahoe & TCP Reno. The graph ...
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1answer
38 views

Hosting a website using dynamic public IP: What if the ISP did not assign any port forwarding? [closed]

Let's just say that I am a peasant that can only avail of a typical Dynamic Public IP address from my ISP. Just for the sake of example, let's say have the following: Domain Name: experiment626....
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2answers
159 views

Which of TCP flags will use a timer, and what Timer will use?

When I study the TCP protocol life cycle, There are 3 stages: Establish Connection Data Transmission Connection Removal TCP have 6 Flag types: SYN, ACK, PSH, FIN, RST, URG. TCP has 4 Timer: ...
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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 ...
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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....
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2answers
100 views

Why router can't be used for converting different model of network but gateway can do this?

We know that Router can't be used for converting different model (e.g OSI model to TCP/IP or TCP/IP model to OSI) of network. It isn't a multiprotocol converter. But gateway is a highly sophisticated ...
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2answers
95 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 ...
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4answers
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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 ...
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1answer
30 views

How a single BGP-process establishes sessions with neighbours in different VRFs?

In VRF-lite solution scenario, when BGP session is established between CE connected to a VRF in PE. The BGP process or in other words TCP server, is listening on port 179(default) for incoming BGP ...
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1answer
51 views

Why in the TCP/IP model the link & physical are one?

I'm currently learning about the OSI model and the TCP/IP models, and I was wondering: Why in the TCP/IP model the physical layer and the data link layer are combined? I'll state how I understand the ...
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2answers
486 views

Why are Internet hosts "not required" to receive an IPv4 datagram larger than 576 bytes?

I'm currently studying Internet protocols and had a question regarding the IP datagram. Within the IP header I am aware there is a field called "total length" which specifies the total ...
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1answer
82 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 ...
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93 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 ...
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1answer
49 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 ...
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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 ...
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3answers
5k views

Why is the last ACK needed in TCP four way termination

As per title. Sorry if this is a duplicate question, but in the numerous posts online, I could only find how a connection is torn down, but not (convincingly) why it is done in such a way. 1. A -----...
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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
19 views

Maximum value of file that can be sent [closed]

this is the following question I have encountered in school. There is a file of X bytes that needs to be transferred from Host A to Host B. The MSS is 10 bytes. What is the maximum value of X such ...
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2answers
159 views

Is it possible for TCP can accept out of order segments?

TCP is connection-oriented protocol whereas IP isn't connection-oriented protocol. Any packets before sending into transport layer sorted operation must have been done in network layer. That's why we ...
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2answers
113 views

Congestion control behaviour of TCP Reno

Which behaviour of TCP Reno after 3 DUP ACK is correct: The one described in the Italian Wikipedia (https://it.wikipedia.org/wiki/Controllo_della_congestione_in_TCP#TCP_Reno). It says the new cwnd is:...
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5answers
447k views

PING port number?

Yesterday interviewer ask me what is port number for ping and which protocol ping use TCP/UDP. After interview I search on internet and found different results someone says ICMP uses Port 7, someone ...
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2answers
68 views

Why does the Transport layer break data into packets? How does that make things reliable? Isn't the Network layer doing the same thing?

I'm new to CNs and there is something that I can't yet grasp. Why doesn't the Transport layer let the Network layer do all the splitting up? How does segmentation make things reliable? Also, I ...
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1answer
11k 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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Why is bandwith-delay product the maximum in-flight datas in TCP? [duplicate]

I have often read, for example https://en.wikipedia.org/wiki/Bandwidth-delay_product that: The result, an amount of data measured in bits (or bytes), is equivalent to the maximum amount of data on ...
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2answers
92 views

Are duplicate sequence numbers from different TCP-connections possible?

While learning about Sequence and Acknowledgment numbers one thing bugged me. I wasn't able to rule out for myself if the following scenario in which Host A sends data to Host B by using some ...
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1answer
228 views

OSI Model vs Network Model: Does It Matter Which One You Use?

The OSI (Open Systems Interconnection) model is comprised of the following layers: 7. Application Layer 6. Presentation Layer 5. Session Layer 4. Transport Layer 3. Network Layer 2. Data Link ...
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5k views

Raw IP communication?

I'm studying the difference between the protocols IP and TCP. IP is said to provide an unreliable datagram service whereas TCP provides a reliable bytestream service. Further, TCP works on top of IP. ...
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1answer
408 views

Why is an empty TCP segment at right edge of receive window not acceptable?

The TCPv4 specification (RFC 793) classifies a received segment as unacceptable if it has zero length, a sequence number equal to RCV.NXT+RCV.WND while the receive window is not zero (second row in ...
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2answers
531 views

TCP Flow-control questions that drives me mad

This is a capture of a TCP session when I was downloading the 10Mb file from an FTP server. The server has an ICW of 10x MSS, so this means that the server can initially send 10 segments without ...
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1answer
5k views

How to determine the throughput of the TCP connection?

APP 1 sends data to APP 2 over a TCP connection through an IP network. The one-way delay is 10ms. The TCP connection bandwidth is 100 Mbps. The system starts up with a WINDOW set at 4,000 bytes....
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2answers
254 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 starts ...
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Definition of a socket [duplicate]

I wanted to confirm whether the definition of a socket I've understood in a computer network context is true. A socket is file who is unique and named by local IP,Local port, Foreign IP and foreign ...

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