8.8 Issue with Using Private AS  Numbers
8.8.4
Configuration example: AS_path manipulation
Note: Click on topology to view command outputs.

In the example, RTF has picked the direct path via AS1 to reach 192.68.11.0/24 because it is shorter. The following configuration shows how the AS_path information can be manipulated to make the AS_path longer by prepending AS path numbers. We will prepend two extra AS path numbers to the AS_path information sent from RTC to RTA to change the RTF decision about reaching 192.68.11.0/24.

The preceding configuration prepends two additional AS_path numbers, 1 and 1, to the AS_path information sent from RTC to RTA. If you look at RTF's BGP table, you will see that RTF can now reach 192.68.11.0/24 via next-hop 192.68.5.2 -- that is, via path 2 1. RTF will prefer this path because it is shorter than the direct path via AS1, which has a path information of 1 1 1.