Questions tagged [udp]

For questions about User Datagram Protocol, a Transport Layer protocol.

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How is congestion avoided when using UDP?

I understand how TCP goes about this - through various methods such as Congestion Window (CWND), Sliding Window, Slow Start and Fast Recovery - it's basically built into the protocol. I understand ...
0 votes
2 answers
47 views

IP packet expired by TTL generate an ICMP response in any case?

Acording to Wikipedia IPv4 article for TTL header field: An eight-bit time to live field limits a datagram's lifetime to prevent network failure in the event of a routing loop. It is specified in ...
1 vote
0 answers
61 views

How I can filter only quic packets with `tcpdump` command?

I want to capture only QUIC UDP datagrams on 443 port. With following command tcpdump reports all udp packets that arrive to the host on port 443. tcpdump -n udp -SX -i any port 443 How I can set it ...
0 votes
0 answers
13 views

What is the maximum safe UDP payload size over IPv6? [duplicate]

I am developing a networking library (that uses exclusively UDP) and I want to support both IPv4 and IPv6 by using a dual-mode socket. I want to limit the size of the packet user can send to a value ...
0 votes
1 answer
152 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 ...
0 votes
1 answer
22 views

Why are External NAT ports different when both NATs are restricted cone? [duplicate]

I'm in the progress of implementing my own Signaling server with UDP hole punching, everything have been smooth up until both hosts were behind Restricted Cone NAT, then the ports for P2P ...
20 votes
5 answers
4k views

Why is Packet Size Limited?

I was reading: this answer to "Maximum packet size for a TCP connection", where it says: The absolute limitation on TCP packet size is 64K (65535 bytes), but in practicality this is far ...
2 votes
1 answer
1k views

Which one is 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
2 answers
93 views

UDP supports multicasting and broadcasting in transport layer or application layer?

We know that UDP does supports multicasting and broadcasting. My question is which layer "UDP supports multicasting and broadcasting"? Is it transport layer or application layer? We know ...
0 votes
0 answers
7 views

How IP packet's payload bigger than the whole former PDU (segment)? [duplicate]

As far as I know: File is too big ---> Fourth layer (TCP or UDP) divide it to a multiple segments ---> Then each segment encapsulated separately into a packet. What means if I have 10 segments, ...
1 vote
2 answers
94 views

Pros and cons of the idea of parallell data transmission

I am learning the basics of internet protocols and related principles. I recently performed experiments comparing UDP and TCP. But when I did that (using the ttcp program) it was only one process and ...
68 votes
5 answers
464k 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 ...
12 votes
7 answers
46k views

Is a DHCP offer packet a broadcast or unicast?

DHCP OFFER is a layer3 broadcast because the server don't know client Ip, but server knows the client mac address. So how it would be the broadcast? If anyone ask me about this? how should I answer? ...
10 votes
2 answers
10k views

How `UDP Hole Punching` Works?

Can anyone explain how UDP hole punching works in a simple way? I know how NAT and PAT works, but can't get a clear idea about UDP hole punching.
-1 votes
2 answers
98 views

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.
0 votes
2 answers
187 views

Do segments at the transport layer contain IP information?

I have few questions about how UDP segments at the transport layer works. I read that The transport layer encapsulates the application layer data along with destination IP and destination port ...
1 vote
0 answers
72 views

Optimize Network For UDP Broadcast Traffic?

I have a computer that creates an AP which multiple microcontrollers connect to. The computer sends out UDP Broadcast packets that tell the microcontrollers to do different things. I have an issue ...
0 votes
1 answer
231 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 ...
-1 votes
1 answer
148 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
1 answer
322 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
1 answer
101 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
2 answers
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
1 answer
50 views

Is there any research that tracks fragmentation and drop rates of UDP packets based on size?

I'm designing a P2P system. I need to decide an ideal packet size that maximizes the efficiency of my system. This answer claims a 508 bytes is the maximum safe size, but I believe larger packets ...
0 votes
1 answer
38 views

Are NAT external:internal mapping types the same for UDP and TCP

Suppose I use a STUN server (UDP) to determine that a client's NAT randomly assigns external port values. Does this imply that the client's NAT will also assign random external port values when using ...
2 votes
1 answer
61 views

Is the distinction between ports under and above port 1024 exists only in TCP and UDP protocols?

Is the distinction between ports under and above port 1024 exists only in TCP and UDP protocols? I want to know if in other protocols (i.e. not TCP and UDP) such a distinction between "root" ...
1 vote
1 answer
47 views

Does UDP can be exposed to stateful analysis?

From protocol theory we know that TCP is stateful protocol. Different stateful packet filters do filtration based on connection state. I.e. it can distinguish responses and replies. It's obviously for ...
0 votes
1 answer
73 views

Is UDP a Transport Layer Protocol in the TCP/IP model?

In some tables explaining the TCP/IP model, both UDP and TCP are set as examples as protocols for the Transport Layer. Does this mean that UDP is part of the TCP/IP protocol suite?
0 votes
1 answer
32 views

The origin of the name UDP

I was wondering, UDP being broadly defined as a connection-less, unreliable protocol giving applications control over messages sequencing and flux control, is it correct to say that the "User&...
1 vote
0 answers
15 views

How to send 10-20KiB with UDP semantics? [closed]

I have volatile traffic, of 10-20KiB, that I want to send with UDP semantics. I have measured packet loss between several servers across the internet. In testing, I can reliably get 32KiB UDP packets ...
1 vote
1 answer
103 views

Does UDP's lack of congestion control clog up the Internet?

I'm reading Computer Networking: A Top-Down Approach, and from what I understand, UDP has no widely adopted mechanism for congestion control like TCP does. Isn't this a problem for the Internet as a ...
0 votes
0 answers
218 views

Unable to get NetFlow flow in Cisco CSR1000v on AWS

I'm trying to use NetFlow Traffic Analyzer of SolarWinds or any NetFlow Monitor in my Cisco CSR1000v routers which are deployed on AWS. I am unable to see any NetFlow flows in the NetFlow Traffic ...
0 votes
1 answer
82 views

CISCO: Copy one UDP unicast packet to other destination

I have following scenario: host A and host B are sending to each other unicast UDP packet. I need that same message from host A will arrive also to host C - with new DST address. How to configure my ...
2 votes
1 answer
67 views

What is the equivalent of "ethernet frames" for satellite communications?

I'm currently implementing error-correction for a UDP-based network protocol. We chose to implement error-correction in order to reduce the number of packet re-transmissions. The architecture is very ...
17 votes
3 answers
3k views

Why does one say IP fragmentation is bad and to be avoided when in reality data always needs to be fragmented for MTU compatibility?

Why does one say fragmentation is bad and must be avoided due to performance issues when in reality fragmentation intrinsically occurs within the communication ? Example: User1 wants to send 100 000 ...
27 votes
8 answers
27k views

Why does DHCP use UDP and not TCP?

DHCP uses UDP as its transport protocol. DHCP messages that a client sends to a server are sent to well-known port 67 (UDP—Bootstrap Protocol and DHCP). DHCP Messages  that a server sends to a client ...
8 votes
4 answers
13k 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 ...
1 vote
2 answers
40 views

Resegment incoming TCP/UDP packet [closed]

The question is as follows: what is the algorithm to resegment an incoming TCP/UDP packet? So, for example, I have a TCP packet, which size is more than some number, and I want to split this packet ...
4 votes
1 answer
9k views

VXLAN: how receiver knows that the received packet is VXLAN-encapsulated?

I'm trying to understand how a receiver knows that the received packet is a VXLAN-encapsulated. Looking at the VXLAN RFC, I can't see anything specific that defines that the packet contains VXLAN ...
2 votes
2 answers
2k views

How are UDP source ports mapped on a NAT?

Here is an example use case; I am curious to see how this is suppose to work and why: Someone has a NAT router from their ISP. Behind the router are 2 PCs running Linux and using ntpd. ntpd sends ...
0 votes
1 answer
16 views

How to ensure packet was created within certain time?

I am creating a custom protocol over UDP and I want to use a low number of bits for the sequence number. This means that the number can wrap relatively fast. Is setting the TTL for the outgoing ...
1 vote
3 answers
63 views

Understanding the ways of communication in IP networks

I am trying to check my understanding about the ways of communication in IP networks. I would classify the ways of communication in IP networks into three generic types: The source requests name ...
0 votes
3 answers
2k views

Does the OSI model support connectionless communication in the transport layer?

In section 7.4.4.1.2 of ISO/IEC 7498-1:1994(E) it begins with: In connectionless-mode, the Transport Layer provides the following functions to support connectionless-mode transmission: But many web ...
0 votes
2 answers
170 views

If you're behind a firewall and all the ports are blocked, how is your browser able to access the internet? [closed]

I'm behind a router and I'm able to run game servers on my home computer after forwarding ports or using the DMZ feature on the router. However, I still don't understand the underlying technology as ...
9 votes
2 answers
11k views

Why maximum length of IP, TCP, UDP packet is not suit?

From many tutorials, I get follow knowledge(maybe I'm misunderstood) : maximum of an Ethernet packet is about 1500 bytes. maximum of an IP packet is about 65535 bytes. maximum of a UDP packet is ...
2 votes
2 answers
2k views

NAT Translation Table Port Number

I had a practice question about a NAT-enabled router with outside address 24.34.112.235 and inside network 192.168.1/24 and three inside hosts .1, .2 and .3. The three hosts all open two connections ...
1 vote
2 answers
4k views

Why traffic shape/police ingress traffic?

Pardon me for my ignorance. I have not tried QoS nor traffic shaping/policing before. I have been pondering on whether can/why would we want to shape/police ingress traffic if you have no control ...
4 votes
3 answers
2k views

port numbers for TCP and UDP

Why do we need both source and destination port numbers in transport layer protocols such as TCP or UDP? What is the purpose for having both?
2 votes
2 answers
3k views

Why do open ports give no response in networking?

Nmap places ports in open|filtered state when it is unable to determine whether a port is open or filtered. This occurs for scan types in which open ports give no response. The lack of response could ...
5 votes
2 answers
6k views

How does a layer-2 switch work with UDP?

If UDP and/or TCP send packets via IP to an Internet Protocol Address, how can a layer-2 switch forward these? Is this possible or do you need a layer-3 switch?
1 vote
2 answers
381 views

Which port determines the protocol?

If we have a common protocol port on both ends.. say source point is 443 and destination port is 80 (hypothetical situation, I know this combination of ports probably makes no sense).. how do we ...

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