-What is the IP TTL (or hop limit if IPv6) in the SYN and RST?
-What does a capture from the client show?
    -Does it receive the SYN-ACK, and does it send the RST?
-What does a traceroute look like?
    -How many hops between the server and the client?
-Is there a firewall, load balancer or other network
 device fronting  (NAT, VIP) the server?
-What do the routing tables look like for the servers
 receiving the No Route to Host?