Cisco router have feature call, VPN pass-trough, that might help to solve your issue.
In order to allow the VPN traffic to pass-through the router, configure an access list that allows these protocols and ports:
Encapsulating Security Payload (ESP) protocol (IP Protocol 50) or Authentication Header (AH) protocol (IP Protocol 51) between the user and the VPN server
User Datagram Protocol (UDP) port 500
UDP port 4500
Refer to this access-list configuration example:
access-list 101 permit esp any anyaccess-list 101 permit udp any any eq 4500access-list 101 permit udp any any eq 500
Once the access-lists are created, bind these to the interface based on the direction, either inbound or outbound, with this command:
ip access-group 101 {in | out}