IS-IS is a link-state routing protocol that uses the SPF algorithm for route calculation. A campus deploys both IPv4 and IPv6 and runs IS-IS to achieve network interconnection.
As shown in the figure, the IPV4 and IPv6 costs of this network are the same, and R1 and R4 only support IPV4. By default, in the IPv6 shortest path tree formed by calculation, the next hop device for R2 to access R6 is: ( ). (Note: the device name must be the same as the figure, such as: R1)