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"autonomous-system" command significance

Answered Question
Mar 30th, 2003
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What is the significance of the command "autonomous-system" in global config mode on a router? When I configure routing protocols I have the option of providing the AS number on the router config command, then why is this command there and when is it used?


Thanks!

Correct Answer by thisisshanky about 14 years 4 months ago

The autonomous-system command is used for EGP - the predecessor of BGP. EGP is configured using the command "router egp ".


Unlike BGP, the EGP configuration command, specifies the remote AS number and not the local AS number. The local AS number is specified using the "autonomous-system " command.


See these router messages for instance, while configuring EGP.


R1(config)#router egp 200

Must give an "autonomous-system " command first


So I have to configure the Local AS first, inorder to configure EGP.


R1(config)#autonomous-system 100

R1(config)#router egp 200

R1(config-router)#


Hope that is clear!

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Overall Rating: 5 (2 ratings)
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tepatel Sun, 03/30/2003 - 12:08
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Number of an autonomous system that identifies the router running routing protocol to other routers running the same routing protocol and tags the routing information passed along.


Like in case of BGP..AS numbers are globally unique numbers that are used to identify ASes, and which enable an AS to exchange exterior routing information between neighboring ASes. An AS is a connected group of IP networks that adhere to a single and clearly defined routing policy.


There are a limited number of available AS numbers. Therefore, it is important to determine which sites require unique AS numbers and which do not. Sites that do not require a unique AS number should use one or more of the AS numbers reserved for private use, which are in the range 64512 - 65535.

visit following url for AS number registration

http://www.arin.net/registration/asn/index.html




Correct Answer
thisisshanky Sun, 03/30/2003 - 15:54
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The autonomous-system command is used for EGP - the predecessor of BGP. EGP is configured using the command "router egp ".


Unlike BGP, the EGP configuration command, specifies the remote AS number and not the local AS number. The local AS number is specified using the "autonomous-system " command.


See these router messages for instance, while configuring EGP.


R1(config)#router egp 200

Must give an "autonomous-system " command first


So I have to configure the Local AS first, inorder to configure EGP.


R1(config)#autonomous-system 100

R1(config)#router egp 200

R1(config-router)#


Hope that is clear!

pbarman Sun, 03/30/2003 - 16:29
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  • Silver, 250 points or more

Thanks Mr. Shanky ! Thats what I needed to know.

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