How to check if a BGP session doesn’t come up:
Doublecheck the configuration on the router and NSX Advanced Load Balancer. Make sure that the peer IPs, subnets, and AS numbers are correct.
Verify the MD5 passwords are the same on the router and NSX Advanced Load Balancer.
Run “show serviceengine bgp” to determine the state of the BGP session initiated by the NSX Advanced Load Balancer SE.
Verify there are no ACLs/route maps on the router preventing the sessions/advertisements.
Additionally, if needed, check the packet capture using tcpdump (tcpdump -M ) on the router and check BGP negotiations.