Routers to Router via switch (subinterfaces)

[Raheel qaiser]

I have attached the diagram

1. Router LHR For WAN (1 physical interface on which using 2 subinterfaces) - Fa0/0 1.0.0.0/24 & Fa0/0.1 3.0.0.0/24

2. Router (ISP) Using 4 physical interfaces (2 of them are connected to the Switch for Router LHR)

Problem is: As Router LHR using subinterfaces and Router ISP using 2 physical interfaces to connect eachothers. How it will be possible!!!

[Reza Sharifi]

You would need to use 2 physical interfaces.  The 2 ISP connections are connecting to the switch which each will go to a different vlan (access ports).  You would need to the the same on your side.  If the ISP would trunk the connection to your switch and use 2 different sub-interfaces, you could do the same on your side.

HTH