Your on-premises data center has 2 routers connected to your GCP 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 the same 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.
" The VPN logs have no-proposal-chosen lines when the VPNs are connecting.
" BGP session is not established between one on-premises router and the Cloud Router.
What is the most likely cause of this problem?
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A. B. C. D.C.
Based on the information provided, the most likely cause of the problem is D. BGP sessions are not established between both on-premises routers and the Cloud Router.
BGP (Border Gateway Protocol) is used to exchange routing information between routers in different autonomous systems (AS) and establish connectivity between them. In this scenario, both on-premises routers are configured with the same ASN, which means that they are in the same autonomous system. When BGP is used between the on-premises routers and the Cloud Router, BGP uses the ASN to establish connectivity between the routers.
If BGP sessions are not established between both on-premises routers and the Cloud Router, then the Cloud Router does not know how to route traffic between the two VPN connections. As a result, all of the traffic is passing across a single VPN instead of being load-balanced across the two connections.
The fact that the VPN logs have no-proposal-chosen lines when the VPNs are connecting also supports the idea that there is a problem with BGP connectivity. This is because BGP is typically used to negotiate and establish the VPN connection.
Option A, that one of the VPN sessions is configured incorrectly, may be a possibility, but this would likely result in one of the VPN connections not working at all, rather than both connections being used but not load-balanced.
Option B, that a firewall is blocking the traffic across the second VPN connection, is less likely because the information provided does not suggest that any firewalls are in place or configured in a way that would cause this issue.
Option C, that there is no load balancer to load-balance the network traffic, is not the most likely cause of the problem because load balancing typically happens at a higher level of the network stack and is not related to BGP connectivity issues.
In summary, the most likely cause of the problem is that BGP sessions are not established between both on-premises routers and the Cloud Router, which is preventing the load-balancing of network traffic across both VPN connections.