Topic 1 Question 15

Professional Cloud Network Engineer

Topic 1 Question 15
Your on-premises data center has 2 routers connected to your Google Cloud environment through a VPN on each router. All applications are working correctly; however, all of the traffic is passing across a single VPN instead of being load-balanced across the 2 connections as desired. During troubleshooting you find: "¢ Each on-premises router is configured with a unique ASN. "¢ Each on-premises router is configured with the same routes and priorities. "¢ Both on-premises routers are configured with a VPN connected to a single Cloud Router. "¢ BGP sessions are established between both on-premises routers and the Cloud Router. "¢ Only 1 of the on-premises router's routes are being added to the routing table. What is the most likely cause of this problem?
- The on-premises routers are configured with the same routes.
- A firewall is blocking the traffic across the second VPN connection.
- You do not have a load balancer to load-balance the network traffic.
- The ASNs being used on the on-premises routers are different.
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- Answer is D: Cloud Router doesn't use ECMP across routes with different origin ASNs
  
  For cases where you have multiple on-premises routers connected to a single Cloud Router, the Cloud Router learns and propagates routes from the router with the lowest ASN. Cloud Router ignores advertised routes from routers with higher ASNs, which might result in unexpected behavior. For example, you might have two on-premises routers advertise routes that are using two different Cloud VPN tunnels. You expect traffic to be load balanced between the tunnels, but Google Cloud uses only one of the tunnels because Cloud Router only propagated routes from the on-premises router with the lower ASN. reference: https://cloud.google.com/network-connectivity/docs/router/support/troubleshooting#ecmp
  
  👍 15
  glk2020/12/14
- D - GCP doesn't run ECMP across different ASNs
  
  👍 9
  Windows982020/11/12
- A
  
  Each on-premises router is configured with a unique ASN = 2 Router with 2 different ASN. Let assume that this router connect to same Core Switch, it is like Triangle Architecture.
  
  Each on-premises router is configured with the same routes and priorities. From inside on premise, assuming they using BGP also, BGP will find the best path. So lets assume that.
  
  How BGP find the best path = https://networklessons.com/bgp/bgp-attributes-and-path-selection
  
  Attributes Weight Local Preference Originate AS path length > As case "Each on-premises router is configured with a unique ASN". So BGP will find the shortest route as possible for this. Origin code MED eBGP path over iBGP path Shortest IGP path to BGP next hop Oldest Path Router ID Neighbor IP address
  
  https://networklessons.com/bgp/how-to-configure-bgp-as-path-prepending
  👍 3
  sagitarius2k2020/06/22
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