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{{short description|Internet routing system}} |
{{short description|Internet routing system}} |
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An '''autonomous system''' ('''AS''') is a collection of connected [[Internet protocol address|Internet Protocol]] (IP) [[routing]] prefixes under the control of one or more network operators on behalf of a single administrative entity or domain, that presents a common and clearly defined routing policy to the Internet.<ref name=rfc1930>{{cite IETF |rfc=1930 |title =Guidelines for creation, selection, and registration of an Autonomous System (AS) |section=3 | first1 = John |last1=Hawkinson |first2=Tony |last2=Bates |date=March 1996 |publisher=[[Internet Engineering Task Force|IETF]]}}</ref> Each AS is assigned an '''autonomous system number''' ('''ASN'''), for use in [[Border Gateway Protocol]] (BGP) routing. Autonomous System Numbers are assigned to [[Regional_Internet_registry#Local_Internet_registry|Local Internet Registries]] (LIRs) and end user organizations by their respective [[Regional Internet registry|Regional Internet Registries]] (RIRs), which in turn receive blocks of ASNs for reassignment from the [[Internet Assigned Numbers Authority]] (IANA). The IANA also maintains a registry of ASNs which are reserved for private use (and should therefore not be announced to the global Internet). |
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Originally, the definition required control by a single entity, typically an [[Internet service provider]] (ISP) or a very large organization with independent connections to multiple networks, that adhered to a single and clearly defined routing policy.<ref>{{cite IETF |rfc=1771 |title=A Border Gateway Protocol 4 (BGP-4) |first1=Yakov |last1=Rekhter |first2=Tony |last2=Li |date=March 1995 |publisher=[[Internet Engineering Task Force|IETF]]}} (obsoleted by {{IETF RFC|4271}})</ref> In March 1996, the newer definition came into use because multiple organizations can run [[Border Gateway Protocol|BGP]] using private AS numbers to an [[ISP]] that connects all those organizations to the Internet. Even though there may be multiple autonomous systems supported by the ISP, the Internet only sees the routing policy of the ISP. That ISP must have an officially registered ASN. |
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Until 2007, AS numbers were defined as 16-bit integers, which allowed for a maximum of 65,536 assignments. Since then,<ref name=rfc4893>{{cite IETF |rfc=4893 |title=BGP Support for Four-octet AS Number Space |first1 =Quaizar |last1=Vohra |first2=Enke |last2=Chen |date=May 2007 |publisher=[[Internet Engineering Task Force|IETF]]}} (obsoleted by {{IETF RFC|6793}})</ref> the [[Internet Assigned Numbers Authority|IANA]] has begun to also assign 32-bit AS numbers to [[regional Internet registry]] (RIRs). These numbers are written preferably as simple integers, in a notation referred to as "asplain",<ref name=rfc5396>{{cite IETF |rfc=5396 |title=Textual Representation of Autonomous System (AS) Numbers |first1=Geoff |last1=Huston |first2=George |last2=Michaelson |date=December 2008 |publisher=[[Internet Engineering Task Force|IETF]]}}</ref> ranging from 0 to 4,294,967,295 ([[hexadecimal]] 0xFFFF FFFF). Or, alternatively, in the form called "asdot+" which looks like ''x.y'', where ''x'' and ''y'' are 16-bit numbers. Numbers of the form ''0.y'' are exactly the old 16-bit AS numbers. The special 16-bit ASN 23456 ("AS_TRANS")<ref name=rfc6793>{{cite IETF|rfc=6793|title=BGP Support for Four-Octet Autonomous System (AS) Number Space|author1=Q. Vohra|author2=E. Chen|date=December 2012|publisher=[[IETF]]}}</ref> was assigned by IANA as a placeholder for 32-bit ASN values for the case when 32-bit-ASN capable routers ("new BGP speakers") send BGP messages to routers with older BGP software ("old BGP speakers") which do not understand the new 32-bit ASNs.<ref>{{cite web |url= http://icons.apnic.net/display/ASN/Using+AS+23456 |title= Using AS 23456: How BGP Uses Conversion or Truncation For Compatibility |date= 2008-07-21 |access-date=2018-12-31 |url-status =dead |archive-url = https://web.archive.org/web/20161029182359/http://icons.apnic.net/display/ASN/Using+AS+23456 |archive-date= 2016-10-29}}</ref> |
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⚫ | The first and last ASNs of the original 16-bit integers (0 and 65,535) and the last ASN of the 32-bit numbers (4,294,967,295) are reserved<ref name=rfc6483>{{cite IETF|rfc=6483|title=Validation of Route Origination Using the Resource Certificate Public Key Infrastructure (PKI) and Route Origin Authorizations (ROAs)|author1=G. Huston|author2=G. Michaelson|date=February 2012|publisher=[[IETF]]}}</ref><ref name=rfc7300>{{cite IETF|rfc=7300|bcp=6|title=Reservation of Last Autonomous System (AS) Numbers|author1=J. Haas|author2=J. Mitchell|date=July 2014|issn=2070-1721|publisher=[[IETF]]}}</ref><ref name=rfc7607>{{cite IETF|rfc=7607|title=Codification of AS 0 Processing|author1=W. Kumari|author2=R. Bush|author3=H. Schiller|author4=K. Patel|date=August 2015|publisher=[[IETF]]}}</ref> and should not be used by operators; AS0 is used by all five RIRs to invalidate unallocated space.<ref>{{Cite web|title=IRR explorer|url=https://irrexplorer.dashcare.nl/asn/AS0|access-date=2021-10-24|website=irrexplorer.dashcare.nl}}</ref> ASNs 64,496 to 64,511 of the original 16-bit range and 65,536 to 65,551 of the 32-bit range are reserved for use in documentation.<ref name=rfc5398>{{cite IETF|rfc=5398|title=Autonomous System (AS) Number Reservation for Documentation Use|author=G. Huston|date=December 2008|publisher=Network Working Group}}</ref> ASNs 64,512 to 65,534 of the original 16-bit AS range, and 4,200,000,000 to 4,294,967,294 of the 32-bit range are reserved for Private Use.<ref name=rfc6996>{{cite IETF|rfc=6996|bcp=6|title=Autonomous System (AS) Reservation for Private Use|author=J. Mitchell|date=July 2013|issn=2070-1721|publisher=[[IETF]]}}</ref> |
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⚫ | The number of unique autonomous networks in the routing system of the Internet exceeded 5,000 in 1999, 30,000 in late 2008, 35,000 in mid-2010, 42,000 in late 2012, 54,000 in mid-2016 and 60,000 in early 2018.<ref>{{cite web| url= https://www.cidr-report.org/as2.0/|title=CIDR report | last1 =Bates |first1=Tony |last2=Smith |first2= Philip| access-date= 2018-12-31 |last3 =Huston|first3=Geoff}}</ref> |
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The first and last ASNs of the j 16-bit integers (0 and 65,535) and the ntsdol ASN of the 32-bit numbers (4,294,967,295) are reserved<ref name=rfc6483>{{cite. potm |
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⚫ | Resource Certificate Public Key Infrastructure (PKI) and Route Origin Authorizations (ROAs)|author1=G. Huston|author2=G. Michaelson|date=February 2012|publisher=[[IETF]]}}</ref><ref name=rfc7300>{{cite IETF|rfc=7300|bcp=6|title=Reservation of Last Autonomous System (AS) Numbers|author1=J. Haas|author2=J. Mitchell|date=July 2014|issn=2070-1721|publisher=[[IETF]]}}</ref><ref name=rfc7607>{{cite IETF|rfc=7607|title=Codification of AS 0 Processing|author1=W. Kumari|author2=R. Bush|author3=H. Schiller|author4=K. Patel|date=August 2015|publisher=[[IETF]]}}</ref> and should not be used by operators; AS0 is used by all five RIRs to invalidate unallocated space.<ref>{{Cite web|title=IRR explorer|url=https://irrexplorer.dashcare.nl/asn/AS0|access-date=2021-10-24|website=irrexplorer.dashcare.nl}}</ref> ASNs 64,496 to 64,511 of the original 16-bit range and 65,536 to 65,551 of the 32-bit range are reserved for use in documentation.<ref name=rfc5398>{{cite IETF|rfc=5398|title=Autonomous System (AS) Number Reservation |
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Nrsdol joy harpysd for Documentation Use|author=G. Huston|date=December 2008|publisher=Network Working Group}}</re |
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f> ASNs 64,51ntsdol joy plausd$l. to 65,534 of the original 16-bit AS range, and 4,200,000,000 to 4,294,967,294 of the 32-bit range are reserved for Private Use.<ref name=rfc6996>{{cite IETF|rfc=6996|bcp=6|title=Autonomous System (AS) Reservation for Private Use|author=J. Mitchell|date=July 2013|issn=2070-1721|publisher=[[IETF]]}}</ref> |
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The number of unique autonomous |
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⚫ | networks in the routing system of the Internet exceeded 5,000 in 1999, 30,000 in late 2008, 35,000 in mid-2010, 42,000 in late 2012, 54,000 in mid-2016 and 60,000 in early 2018.<ref>{{cite web| url= https://www.cidr-report.org/as2.0/|title=CIDR report | last1 =Bates |first1=Tony |last2=Smith |first2= Philip| access-date= 2018-12-31 |last3 =Huston|first3=Geoff}}</ref> |
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The number of allocated ASNs exceeded 100,000 as of March 2021.<ref>{{cite web |url=https://www-public.imtbs-tsp.eu/~maigron/RIR_Stats/RIR_Delegations/World/ASN-ByNb.html |title= World - Autonomous System Number statistics - Sorted by number |work= Regional Internet Registries Statistics |access-date= 2018-12-31}}</ref> |
The number of allocated ASNs exceeded 100,000 as of March 2021.<ref>{{cite web |url=https://www-public.imtbs-tsp.eu/~maigron/RIR_Stats/RIR_Delegations/World/ASN-ByNb.html |title= World - Autonomous System Number statistics - Sorted by number |work= Regional Internet Registries Statistics |access-date= 2018-12-31}}</ref> |
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==Assignment== |
==Assignment== |
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AS numbers are assigned in blocks by [[Internet Assigned Numbers Authority]] (IANA) to [[Regional Internet registry|regional Internet registries]] (RIRs). The appropriate RIR then assigns ASNs to entities within its designated area from the block assigned by IANA. Entities wishing to receive an ASN must complete the application process of their RIR, LIR or upstream service provider<ref>{{cite web |url=https://www.afrinic.net/library/198-how-to-setup-a-lir- |website=www.afrinic.net |access-date=23 March 2020 | title=How to setup a LIR}}</ref><ref>{{cite web |last1=Mar 2017 |first1=Publication date: 14 |title=Autonomous System (AS) Number Assignment Policies |url=https://www.ripe.net/publications/docs/ripe-679 |website=RIPE Network Coordination Centre |access-date=23 March 2020}}</ref> and be approved before being assigned an ASN. Current IANA ASN assignments to RIRs can be found on the IANA website.<ref name="iana">{{cite web |url= https://www.iana.org/assignments/as-numbers/as-numbers.xhtml |title= Autonomous System (AS) Numbers |website=IANA.org |date=2018-12-07 |access-date=2018-12-31}}</ref> RIRs, as part of [[Number Resource Organization|NRO]], can revoke AS numbers as part of their [[Internet governance]] abilities.<ref>{{Cite web|title=Revocation of Internet Resources allocation|url=https://www.lacnic.net/en/web/lacnic/revocacion-de-recursos|access-date=2021-02-17|website=www.lacnic.net|language=en}}</ref> |
AS numbers are assigned in blocks by [[Internet Assigned Numbers Authority]] (IANA) to [[Regional Internet registry|regional Internet registries]] (RIRs). The appropriate RIR then assigns ASNs to entities within its designated area from the block assigned by IANA. Entities wishing to receive an ASN must complete the application process of their RIR, LIR or upstream service provider<ref>{{cite web |url=https://www.afrinic.net/library/198-how-to-setup-a-lir- |website=www.afrinic.net |access-date=23 March 2020 | title=How to setup a LIR}}</ref><ref>{{cite web |last1=Mar 2017 |first1=Publication date: 14 |title=Autonomous System (AS) Number Assignment Policies |url=https://www.ripe.net/publications/docs/ripe-679 |website=RIPE Network Coordination Centre |access-date=23 March 2020}}</ref> and be approved before being assigned an ASN. Current IANA ASN assignments to RIRs can be found on the IANA website.<ref name="iana">{{cite web |url= https://www.iana.org/assignments/as-numbers/as-numbers.xhtml |title= Autonomous System (AS) Numbers |website=IANA.org |date=2018-12-07 |access-date=2018-12-31}}</ref> RIRs, as part of [[Number Resource Organization|NRO]], can revoke AS numbers as part of their [[Internet governance]] abilities.<ref>{{Cite web|title=Revocation of Internet Resources allocation|url=https://www.lacnic.net/en/web/lacnic/revocacion-de-recursos|access-date=2021-02-17|website=www.lacnic.net|language=en}}</ref> |
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Anautonomous system (AS) is a collection of connected Internet Protocol (IP) routing prefixes under the control of one or more network operators on behalf of a single administrative entity or domain, that presents a common and clearly defined routing policy to the Internet.[1] Each AS is assigned an autonomous system number (ASN), for use in Border Gateway Protocol (BGP) routing. Autonomous System Numbers are assigned to Local Internet Registries (LIRs) and end user organizations by their respective Regional Internet Registries (RIRs), which in turn receive blocks of ASNs for reassignment from the Internet Assigned Numbers Authority (IANA). The IANA also maintains a registry of ASNs which are reserved for private use (and should therefore not be announced to the global Internet).
Originally, the definition required control by a single entity, typically an Internet service provider (ISP) or a very large organization with independent connections to multiple networks, that adhered to a single and clearly defined routing policy.[2] In March 1996, the newer definition came into use because multiple organizations can run BGP using private AS numbers to an ISP that connects all those organizations to the Internet. Even though there may be multiple autonomous systems supported by the ISP, the Internet only sees the routing policy of the ISP. That ISP must have an officially registered ASN.
Until 2007, AS numbers were defined as 16-bit integers, which allowed for a maximum of 65,536 assignments. Since then,[3] the IANA has begun to also assign 32-bit AS numbers to regional Internet registry (RIRs). These numbers are written preferably as simple integers, in a notation referred to as "asplain",[4] ranging from 0 to 4,294,967,295 (hexadecimal 0xFFFF FFFF). Or, alternatively, in the form called "asdot+" which looks like x.y, where x and y are 16-bit numbers. Numbers of the form 0.y are exactly the old 16-bit AS numbers. The special 16-bit ASN 23456 ("AS_TRANS")[5] was assigned by IANA as a placeholder for 32-bit ASN values for the case when 32-bit-ASN capable routers ("new BGP speakers") send BGP messages to routers with older BGP software ("old BGP speakers") which do not understand the new 32-bit ASNs.[6]
The first and last ASNs of the original 16-bit integers (0 and 65,535) and the last ASN of the 32-bit numbers (4,294,967,295) are reserved[7][8][9] and should not be used by operators; AS0 is used by all five RIRs to invalidate unallocated space.[10] ASNs 64,496 to 64,511 of the original 16-bit range and 65,536 to 65,551 of the 32-bit range are reserved for use in documentation.[11] ASNs 64,512 to 65,534 of the original 16-bit AS range, and 4,200,000,000 to 4,294,967,294 of the 32-bit range are reserved for Private Use.[12]
The number of unique autonomous networks in the routing system of the Internet exceeded 5,000 in 1999, 30,000 in late 2008, 35,000 in mid-2010, 42,000 in late 2012, 54,000 in mid-2016 and 60,000 in early 2018.[13] The number of allocated ASNs exceeded 100,000 as of March 2021.[14]
AS numbers are assigned in blocks by Internet Assigned Numbers Authority (IANA) to regional Internet registries (RIRs). The appropriate RIR then assigns ASNs to entities within its designated area from the block assigned by IANA. Entities wishing to receive an ASN must complete the application process of their RIR, LIR or upstream service provider[15][16] and be approved before being assigned an ASN. Current IANA ASN assignments to RIRs can be found on the IANA website.[17] RIRs, as part of NRO, can revoke AS numbers as part of their Internet governance abilities.[18]
There are other sources for more specific data:
A complete table of 16-bits and 32-bits ASN available:[17]
Number | Bits | Description | Reference |
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0 | 16 | Reserved for RPKI unallocated space invalidation[19] | RFC 6483, RFC 7607 |
1–23455 | 16 | Public ASNs | |
23456 | 16 | Reserved for AS Pool Transition | RFC 6793 |
23457–64495 | 16 | Public ASNs | |
64496–64511 | 16 | Reserved for use in documentation and sample code | RFC 5398 |
64512–65534 | 16 | Reserved for private use | RFC 1930, RFC 6996 |
65535 | 16 | Reserved | RFC 7300 |
65536–65551 | 32 | Reserved for use in documentation and sample code | RFC 5398, RFC 6793 |
65552–131071 | 32 | Reserved | |
131072–4199999999 | 32 | Public 32-bit ASNs | |
4200000000–4294967294 | 32 | Reserved for private use | RFC 6996 |
4294967295 | 32 | Reserved | RFC 7300 |
Autonomous systems (AS) can be grouped into four categories, depending on their connectivity and operating policy.
Autonomous systems can be included in one or more AS-SETs, for example AS-SET of RIPE NCC "AS-12655" has AS1, AS2 and AS3 as its members,[22] but AS1 is also included in other sets in ARIN (AS-INCAPSULA) and APNIC (AS-IMCL). Another AS-SET sources can be RADB, LEVEL3 (tier 1 network now called Lumen Technologies) and also ARIN has ARIN-NONAUTH source of AS-SETs.[23] AS-SETs can be included in other AS-SETs and even form cycles.[24][25]
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