Questions tagged [udp]

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

42
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4answers
226k 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 different results someone says ICMP uses Port 7,...
18
votes
3answers
6k views

What do TCP/UDP add to “raw ip”?

I know that both TCP and UDP are built on top of IP, and I know the differences between TCP & UDP, but I'm confused about what exactly "raw ip" is. Would it be fair to say that TCP & UDP both ...
18
votes
4answers
12k views

What does a UDP connection timeout really mean?

Since UDP is a connectionless protocol, I'm confused by the setting on my Sonicwall Firewall for "UDP Connection Timeout". It's set at a default of 30 seconds -- but what exactly times out after 30 ...
12
votes
3answers
46k views

How to verify that a UDP port is open? [closed]

I have here a dilemma. I have a device that communicates to another remote device but there is a firewall between them. It's a UDP connection, so TCP utilities don't work to test if the specific port ...
8
votes
4answers
22k 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. ...
8
votes
1answer
1k views

UDP hole punching NAT port

I just read an article about the process of "punching holes" with the UDP protocol. I understand how it's done, but I have one last question to clear up things. We have the rendezvous server and ...
7
votes
2answers
926 views

How does NAT work with incoming UDP packets from unknown IP

Apologies in advance for the relatively noob question and if this is off topic here ( I am not sure...) The situation is that I have a UDP client and server bound to the same port. My understanding ...
7
votes
1answer
230 views

Throttling among Data Centers

In general, links among data centers are shared (having shared network infrastructure). Thus, I can't detect the available bandwidth in between two data centers that may vary every while and through ...
6
votes
5answers
2k 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 ...
6
votes
3answers
14k views

Traceroute Over TCP vs UDP

For what purpose would one wish to send traceroute over TCP rather than UDP? What advantages/disadvantages are there in doing so? I know that traceroute normally uses UDP ICMP "echo" packets while ...
6
votes
3answers
761 views

Does a switch always get a MAC address from a PC?

I was wondering if there is a possibility that a switch won't get the needed MAC address to it's CAM. For example, if the used protocol is UDP, where the sender doesn't need an answer back from the ...
6
votes
2answers
2k 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 ...
6
votes
3answers
570 views

Is UDP Usage in Routing Information Protocol (RIP) a Secure Practice?

I know that UDP is a connectionless transport layer protocol. Since it is easy to fake your source IP and source Port in your headers, what keeps anyone from poisoning routing tables via RIP? It seems ...
6
votes
4answers
2k 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 ...
6
votes
0answers
255 views

How to control unwanted UDP traffic (Broadcast & Multicast) on Cisco Router 2911?

Please suggest, we are getting UDP traffic either broadcast or multicast in router 2911 which cause 95%+ utilisation of the router. And we got error in link and business impact due to this. Company ...
5
votes
4answers
22k 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? ...
5
votes
3answers
9k views

Packet forwarding in TCP vs UDP

Recently I had a discussion about differences between TCP and UDP, and the other person insisted that there's a difference in packet forwarding: The packets in a TCP connection follow an established ...
5
votes
2answers
476 views

Does implementing some level of reliability in UDP packets defeat its purpose over using TCP?

Considering UDP packets can get lost or arrive late to their target destination, does it make more sense to: Use a TCP socket for important messages & events (ex: in a game where a player gets ...
5
votes
1answer
534 views

How does UDP NAT Know When To Remove The Rule

So say you are a user behind a NAT/router on an internal network. You begin sending UDP data to an internet-facing server. The packet hits your router, it inserts an entry to allow returning packets ...
5
votes
2answers
2k views

Why does IKE use UDP instead of TCP?

Why does IKE use UDP, and handle any retransmission itself? (Larger IKE packets may cause UDP fragmentation and are dropped by some ISPs: IKE over TCP.
5
votes
1answer
3k 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.
5
votes
2answers
3k 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?
5
votes
1answer
1k views

What is the reason for the different order of the Source and Destination in a L2 header?

A TCP/UDP header (Layer 4) lists the Source Port, then the Destination Port: An IP header (Layer 3) lists the Source IP, then the Destination IP: An Ethernet header (L2) and a WiFi Header (L2) lists ...
5
votes
1answer
903 views

why RIP sending only maximum of 512 bytes of data

When RIP router sends update to routers, why it is limited to use only 512 bytes of UDP data. Why not more than that, even when it has a 1500 byte MTU. How is the maximum of 512 bytes determined?
5
votes
2answers
345 views

Does the NAT source UDP port depend only on src ip/port?

Does the NAT UDP port depend only on src ip/port? Suppose I have a two networks connected via a NAT/router using Source NAT. PC A (192.168.0.2) in Network A (with router 192.168.0.1) sends a UDP ...
4
votes
2answers
63 views

Is it correct to assume that ordering of frames at switch level is not important?

My understanding is that if the payload of the frame contains any data that needs to be reassembled, at least for TCP payload, it can be done at the OS level, once all the packets are received and ...
4
votes
1answer
99 views

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: ...
4
votes
3answers
753 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?
4
votes
2answers
11k views

How to find out TCP/UDP latency of your network?

Many people often suggest you to use ping command to find out your network latency. But it is false and a myth you often find in articles on Internet. ICMP ping was never designed to find out latency ...
4
votes
2answers
1k views

IPERF TCP vs UDP

I had to determine UDP performance over multi-hop network , I used MAC Air over gigabit ethernet ( Thunderbolt). As is customary, TCP was tested and the gig over link was saturated ~900mbps, but ...
4
votes
1answer
141 views

Copying bytes from Wireshark

Should it be possible for someone to export the binary payload (say from a UDP packet) captured from Wireshark and later send this stream as a "valid" UDP packet? Longer story: I've captured a DNS ...
4
votes
2answers
960 views

Difference between UDP and TCP

http://www.dummies.com/how-to/content/the-tcpip-networking-protocol-suite.html I was reading the difference between the two, and in the example of TCP: For example, when a user running a Web browser ...
4
votes
1answer
8k views

UDP Port Forwarding Range

We just purchased a cisco 3825 router running IOS 15.1. The slice of the topology in question is as follows: RTP (8000-20000) RTP (8000-20000) 192.168.2.1 <-------------->...
3
votes
3answers
22k views

Sending generic UDP traffic for Network Simulation

I need to test an application which drops a user-specified percentage of packets. Right now, it will drop any packet type which I can easily verify by sending pings and observing the ICMP messages in ...
3
votes
2answers
2k views

When is TFTP used? [closed]

It seems like a strange idea to transfer files using a connectionless protocol - so in what situation would you not care about if the entire file is delivered or not? I read somewhere that TFTP is ...
3
votes
1answer
2k views

Traceroute UDP port question

I know, that traceroute uses UDP, and for destination port it starts with 33434. Then, with each next hop it increments the destination port number by 1. The questions is: why does traceroute need to ...
3
votes
1answer
7k 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 ...
3
votes
1answer
323 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 ...
3
votes
1answer
186 views

Satellite Internet Connection - Faster Speed?

I acknowledge the fact that satellite internet maybe quite slow and have high latency. This is generally true for TCP applications like HTTP, FTP etc. If a UDP VPN connection was to be setup between ...
3
votes
3answers
7k views

Why do i only see QUIC and not UDP during capture in wireshark?

I've been using wireshark and noticed that I no longer see UDP but QUIC, why is this the case?
3
votes
1answer
166 views

Packet with wrong source MAC address

When I send a UDP packet with wrong source MAC address but with right source IP address, assuming a reply is sent, will I get the reply because I have right source IP address, or I will not get the ...
3
votes
2answers
4k views

Should I increase the timeout value for UDP on our VPN router-device?

We have a SonicWALL NSA 2400. We have numerous (100+) personnel in different offices in different physical locations that establish VPN sessions successfully every day. Some of these client computers ...
3
votes
3answers
2k views

DNS Resolution:<Backwards IP Address>.in-addr.arpa [closed]

Can somebody please explain whats going on here? localuser@localhost:~$ host 127.0.0.1 1.0.0.127.in-addr.arpa domain name pointer localhost. What's up with the IP address being resolved ...
3
votes
1answer
3k views

Is it possible to have same multicast group members listening on different port numbers?

Let's say I have a multicast group 239.0.0.1. If A and B are members of this group and listening on port 6000, I can send data to (239.0.0.1, 6000) and both A and B will receive. Now, if A is ...
3
votes
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 ...
3
votes
1answer
233 views

802.11 multicast buffering due to random back-off mechanism

I am trying to achieve periodic multicast with WAP (Wireless Access Point) [basically trying to stream real time audio data to multiple devices]. The regularity in the interval between successive UDP ...
3
votes
1answer
152 views

rate-limit dns queries on HP procurve 8212zl

I had ast week the situation that a user accidentally got our DNS server to its knees by sending over 270K DNS queries to our dnsmasq. I was looking for a reliable method to prevent this Happening in ...
2
votes
3answers
6k views

how to make udp reliable

In a job interview i had faced a question that In my company we always use udp because it is very much fast. and we have reliability also. can u answer how? without adding so much overhead to the udp ...
2
votes
3answers
5k views

Can two different applications bind the same port on a host if they use different protocols?

So my question is quite clear I think. If two applications use different transport layer protocols (e.g. TCP and UDP or something else) can they open the same port number? How does the OS do the ...
2
votes
4answers
243 views

Tcp reliabity handled at hardware level?

At work we are moving from a TCP to a UDP protocol for a kind of 3D engine because we have 1s hang when a packet is lost. Since our engine is not designed to handle packet loss nor out of order ...