AskDefine | Define stun

Dictionary Definition



1 make senseless or dizzy by or as if by a blow; "stun fish" [syn: stupefy]
2 surprise greatly; knock someone's socks off; "I was floored when I heard that I was promoted" [syn: shock, floor, ball over, blow out of the water, take aback]
3 hit something or somebody as if with a sandbag [syn: sandbag]
4 overcome as with astonishment or disbelief; "The news stunned her" [syn: bedaze, daze] [also: stunning, stunned]

User Contributed Dictionary



  • /stʌn/, /stVn/
    Rhymes: -ʌn


  1. To incapacitate.
    Bill tried to stun the snake by striking it on the head.
    In many European countries cattle has to be stunned before slaughtering.
    He stood there stunned, looking at the beautiful, breath-taking sunrise.
  2. To shock or surprise.
    The celebrity was stunned to find herself confronted with unfounded allegiations on the front page of a newspaper.


to incapacitate
to shock or surprise

Extensive Definition

Simple Traversal of UDP through NATs (STUN), is a network protocol allowing a client behind a NAT (Network Address Translator) to find out its public address, the type of NAT it is behind and the internet-side port associated by the NAT with a particular local port. This information is used to set up UDP (User Datagram Protocol) communication between two hosts that are both behind NAT routers. The protocol is defined in RFC 3489.

Protocol overview

STUN is a client-server protocol. A VoIP phone or software package may include a STUN client, which will send a request to a STUN server. The server then reports back to the STUN client what the public IP address of the NAT router is, and what port was opened by the NAT to allow incoming traffic back in to the network.
The response also allows the STUN client to determine what type of NAT is in use, as different types of NATs handle incoming UDP packets differently. It will work with three of four main types: full cone, restricted cone, and port restricted cone. (In the case of restricted cone or port restricted cone NATs, the client must send out a packet to the endpoint before the NAT will allow packets from the endpoint through to the client.) STUN will not work with symmetric NAT (also known as bi-directional NAT) which is often found in the networks of large companies. With symmetric NAT, the IP address of the STUN server is different than that of the endpoint, and therefore the NAT mapping the STUN server sees is different than the mapping that the endpoint would use to send packets through to the client. For details on the different types of NAT, see network address translation.
Once a client has discovered its external addresses, it can relate it to its peers. If the NATs are full cone then either side can initiate communication. If they are restricted cone or restricted port cone both sides must start transmitting together.
Note that using the techniques described in the STUN RFC does not necessarily require using the STUN protocol; they can be used in the design of any UDP-based protocol.
Protocols like SIP use UDP packets for the transfer of sound/video/text signaling traffic over the Internet. Unfortunately as both endpoints are often behind NAT, a connection cannot be set up in the traditional way. This is where STUN is useful.
The STUN server is contacted on UDP port 3478, however the server will give hints to clients to perform tests on alternate IP address and port number too (STUN servers have two IP addresses). The RFC states that this port and IP address are arbitrary.


STUN uses the following algorithm (adapted from RFC 3489) to discover the presence of NAT gateways and firewalls:
Where the path through the diagram ends in a red box, UDP communication is not possible. Where the path ends in a yellow or green box, communication is possible.

External links

stun in Czech: Simple traversal of UDP over NATs
stun in German: STUN
stun in Spanish: STUN
stun in French: STUN
stun in Italian: STUN
stun in Polish: STUN
stun in Russian: STUN
stun in Swedish: STUN
stun in Vietnamese: STUN
stun in Chinese: STUN

Synonyms, Antonyms and Related Words

KO, amaze, anesthetize, appall, astonish, astound, awake the dead, awe, awestrike, bedaze, bedazzle, bemuse, benumb, besot, bewilder, blast, blast the ear, blunt, boggle, boom, bowl down, bowl over, chloroform, coldcock, confound, crash, crescendo, daze, dazzle, deaden, deafen, desensitize, din, discombobulate, dope, drug, dull, dumbfound, dumbfounder, electrify, etherize, fill the air, flabbergast, freeze, frighten, horrify, jar, jolt, kayo, knock out, knock senseless, knock stiff, knock unconscious, lay out, narcotize, nonplus, numb, obtund, overcome, overwhelm, palsy, paralyze, peal, perplex, petrify, put to sleep, rattle the windows, rend the air, rend the ears, resound, ring, rise, rock the sky, scare stiff, scare to death, shake, shake up, shock, split the eardrums, split the ears, stagger, startle, startle the echoes, strike dead, strike dumb, strike terror into, strike with wonder, stupefy, surge, surprise, swell, take aback, terrify, thunder
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