Editing Inter-Asterisk eXchange

{{redirect|IAX|the airline with the ICAO code IAX|Island Express Air|the Type Iax supernova|Type Iax supernova}}
{{Infobox networking protocol
| title        = Inter-Asterisk eXchange
| logo         = 
| logo alt     = 
| image        = 
| image alt    = 
| caption      = 
| is stack     = 
| abbreviation = IAX
| purpose      = [[Voice over IP|VoIP]]
| developer    = [[Mark Spencer (computer engineer)|Mark Spencer]]
| date         = {{Start date and age|    |  |  }}<!--Fill in: Year (4 digits), month and day (2 digits)-->
| based on     = 
| influenced   = IAX2
| osilayer     = [[Application layer]]
| ports        = 4569
| rfcs         = {{IETF RFC|5456|link=no}}
| hardware     = 
}}
{{IPstack}}
'''Inter-Asterisk eXchange''' ('''IAX''') is a [[communications protocol]] native to the [[Asterisk (PBX)|Asterisk]] [[private branch exchange]] (PBX) software, and is supported by a few other [[softswitch]]es, PBX systems, and [[softphone]]s.  It is used for transporting [[voice over IP]] telephony sessions [[inter-server|between servers]] and to terminal devices.

The original IAX protocol is [[deprecated]] and has been superseded by a second version, commonly called IAX2. The IAX2 protocol was published as an [[Request for Comments#Status "informational"|informational]] (non-standards-track) RFC 5456 by discretion of the RFC Editor in February 2010.<ref>RFC 5456, page 1: "Status of This Memo  This memo provides information for the Internet community.  It does not specify an Internet standard of any kind."</ref>

==Basic properties==
IAX is a binary-encoded [[voice over Internet protocol]] (VoIP) that is used for streaming media, but is primarily designed for IP voice calls.

IAX uses a single [[User Datagram Protocol]] (UDP) data stream and [[port number]], by default 4569, between endpoints for both session [[signal (information theory)|signaling]] and media payloads. This feature provides benefits for traversing [[network address translator]]s at network boundaries, as it simplifies [[firewall (networking)|firewall]] configuration. Other VoIP protocols typically use independent channels for signaling and media, such as the [[Session Initiation Protocol]] (SIP), [[H.323]], and the [[Media Gateway Control Protocol]] (MGCP), which carry media with the [[Real-time Transport Protocol]] (RTP).

IAX supports [[trunking]], [[multiplexing]] channels over a single link. When [[trunking]], data from multiple sessions are merged into a single stream of [[packet (information technology)|packet]]s between two endpoints, reducing the IP overhead. This is advantageous in VoIP transmissions, in which IP headers use a large fraction of [[Bandwidth (computing)|bandwidth]].

IAX2 supports native encryption of both control and media streams using [[AES-128]].

==Origin==
Both versions of the IAX protocol were created by [[Mark Spencer (computer engineer)|Mark Spencer]] and much of the development was carried out in the Asterisk open-source community.

==Goals==
The primary goals for IAX are to minimize bandwidth used in media transmissions, and to provide native [[network address translation]] (NAT) transparency.  It was intended to be easy to use behind [[Firewall (networking)|firewalls]].

==Drawbacks==
* Awkward extensibility: Due to the lack of a generic extension mechanism, new features have to be added in the protocol specification, which makes the protocol less flexible than [[H.323]], [[Session Initiation Protocol|SIP]], and [[Media Gateway Control Protocol|MGCP]].
* Vulnerability: Older implementations of IAX2 were vulnerable to resource exhaustion DoS attack methods that are available to the public.{{citation needed|date=May 2013}}  While no solutions existed for these issues,  the best practices included limiting UDP port access to specific trusted IP addresses. Internet-facing IAX2 ports are considered vulnerable and should be monitored closely. The [[fuzzer]] used to detect these application vulnerabilities was posted on [[milw0rm]].<ref>{{cite web
| url=http://milw0rm.com/exploits/8940
| title=udp IAX protocol fuzzer
| first=Blake
| last=Cornell
| publisher=[[milw0rm]]
| archive-url=https://web.archive.org/web/20100214061758/http://milw0rm.com/exploits/8940
| archive-date=2010-02-14
| url-status=dead
}}</ref> and is included in the ''VoIPer'' development tree.<ref>{{cite web
| url=http://sourceforge.net/p/voiper/code/HEAD/tree/trunk/iaxFuzzer/iaxFuzz.pl
| title=udp IAX protocol fuzzer
| first=Blake
| last=Cornell
| date=2009-05-19
| publisher=VoIPER : VoIP Exploit Research toolkit
| access-date=2013-05-28}}</ref> These issues were briefly mentioned in the IAX RFC 5456 on page 94. This flaw does not exist in up-to-date installations.<ref>{{cite web
| url=http://downloads.asterisk.org/pub/security/AST-2009-006.html
| title=Asterisk Project Security Advisory - AST-2009-006
| date=2009-09-03
| author=Russell Bryant
| publisher=[[Asterisk (PBX)|Asterisk]]
| access-date=2013-05-28
}}</ref>

==References==
{{Reflist}}

==External links==
* {{IETF RFC|5456|link=no}} IAX: Inter-Asterisk eXchange Version 2
* {{IETF RFC|6315|link=no}} IANA Registration for Enumservice 'iax'
* {{cite book
| title=Inter-Asterisk Exchange (IAX): Deployment Scenarios in SIP-Enabled Networks
| first=Mohamed
| last=Boucadair
| date=February 2009
| publisher=[[John Wiley & Sons|Wiley]]
| url=http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470770724.html
| isbn=978-0-470-77072-6}}


{{DEFAULTSORT:Inter-Asterisk Exchange}}
[[Category:VoIP protocols]]
[[Category:Asterisk (PBX)]]
[[Category:Application layer protocols]]