How does the use of private AS numbers affect BGP security and advertising on the public Internet?

• A. Private ASNs are globally unique.
• B. Private ASNs are not globally unique; misinterpretation, collision risk; avoid advertising private ASNs on the public Internet.
• C. They enhance security.
• D. They are recommended for public Internet.

Answer: (B)

Private AS numbers are reserved for private use and are not globally unique. In BGP, globally unique ASNs are needed so every network can identify the true origin of a route and apply consistent policies across the Internet. When private ASNs appear in routes advertised to the public Internet, different networks might interpret the same private number as belonging to different organizations, leading to path misinterpretation or collisions. That’s why the best practice is to avoid advertising private ASNs on public peering; keep private numbers inside your own networks or use them only in contexts that do not cross public borders, and use a globally unique ASN for routes that traverse the Internet. The other statements aren’t correct: private ASNs are not globally unique, they don’t inherently strengthen security, and they are not recommended for public Internet advertising.