8.8 Issue with Using Private AS  Numbers
8.8.2
Configuration example: removing private AS numbers
This example demonstrates how BGP can be configured to prevent the leakage of private AS numbers into the Internet. Consider the figure; AS1 will prevent private AS number 65001 from being leaked to the Internet when BGP routes are propagated.
Lab Activity
  In this lab, you will learn how to configure BGP to prevent the leakage of Private AS numbers onto the Internet.

Note: Click on topology to view command outputs.

Note how RTC is using the remove-private-AS keyword in its neighbor connection to AS7. The following output shows the BGP tables of RTC and RTE.

Note that prefix 172.16.220.0/24 has an AS_path of 65001 in the RTC BGP table and an AS_path of 1 in the RTE BGP table. RTC has stripped the private AS path information when propagating the update to AS7.