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Silver

"autonomous-system" command significance

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!

1 ACCEPTED SOLUTION

Accepted Solutions

Re: "autonomous-system" command significance

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!

3 REPLIES
Cisco Employee

Re: "autonomous-system" command significance

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

Re: "autonomous-system" command significance

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!

Silver

Re: "autonomous-system" command significance

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

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