Private AS Number Propagation

Private AS numbers should not be advertised into the Internet.

The private AS numbers must be removed from the AS path before the customer BGP routes are advertised to other service providers.

Private AS numbers should not be advertised into the Internet.

The private AS numbers must be removed from the AS path before the customer BGP routes are advertised to other service providers.

Routes that are received by the ISP from the customer are propagated to the rest of the Internet only if they are part of the provider-independent (PI) address space.

When the ISP receives BGP routes from the customer, the AS-path attribute of the received routes contains only the AS number of the customer. If the customer uses AS-path prepending, there may be several repetitions of the customer AS number in the AS path. If customer routes are propagated by the service provider to the Internet, the AS number of the customer will be present in the AS path unless it is explicitly removed.

Note If the customer has been assigned a private AS number, this AS number must never be advertised by any router to the rest of the Internet.

Removal of a private AS number from the AS path is accomplished by using the remove-private-as command on the ISP EBGP sessions with the rest of the Internet. In the figure, removal of the private AS number takes place on the EBGP session between AS 387 and AS 217.

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