In such environment, router supports multiple VPN tunnels pass through.
- PC1 (VPN-IPsec) <--> router <--> Internet <--> VPN servers
- PC can create multiple tunnels with different servers.
But if two PCs in LAN environment, the second PC cannot initial to establish a tunnel if PC1 has established a tunnel already. Because the returned packet from VPN server can not be forwarded correctly to the initial PC, returned packet from WAN site carries the same port and same destination IP address.