Part-3- Visualized Enterprise Internet Multi-Homing Design – Technical Design Considerations

Part-2 of this blog series discussed some of the key design consideration of enterprise multi-homing. Also in part-2 the following scenario was presented and this blog will analyze it and address it.

  • ISP-A owns AS 105 and ISP-B owns AS 106
  • Customer-X with AS 65001 is multi-homed to both ISPs, AS 105 and AS 106
  • ISP-B allocated the public IP range (PA) to Customer-X
  • Customer-X advertised this range over both links toward both ISPs

Customer-X goal is use upstream AS 106 as the primary path for both inbound and outbound traffic for, and AS 105 as the back path.

based on the provided information, do you see any issue(s) to achieve Customer-X traffic routing goal? If yes, what and why?

Common misconception:

Note: with the PI IP range you may be able to advertise longer subnet than /22 but this has to be confirmed with your direct peering ISP(s)


Marwan Al-shawi – CCDE No. 20130066, Google Cloud Certified Architect, AWS Certified Solutions Architect, Cisco Press author (author of the Top Cisco Certifications’ Design Books “CCDE Study Guide and the upcoming CCDP Arch 4th Edition”). He is Experienced Technical Architect. Marwan has been in the networking industry for more than 12 years and has been involved in architecting, designing, and implementing various large-scale networks, some of which are global service provider-grade networks. Marwan holds a Master of Science degree in internetworking from the University of Technology, Sydney. Marwan enjoys helping and assessing others, Therefore, he was selected as a Cisco Designated VIP by the Cisco Support Community (CSC) (official Cisco Systems forums) in 2012, and by the Solutions and Architectures subcommunity in 2014. In addition, Marwan was selected as a member of the Cisco Champions program in 2015 and 2016.