R2
interface Tunnel0
 ip unnumbered Serial1/0
 tunnel source 12.12.12.2
 tunnel destination 12.12.12.1
!
interface Serial1/0
 ip address 12.12.12.2 255.255.255.0
!
interface Serial1/1
 ip address 24.24.24.2 255.255.255.0
!
ip route 13.13.13.0 255.255.255.0 Tunnel0
 
 
=========================================================
R1
interface Tunnel0
 ip unnumbered Serial1/0
 tunnel source 12.12.12.1
 tunnel destination 12.12.12.2
!
interface Serial1/0
 ip address 12.12.12.1 255.255.255.0
!
interface Serial1/1
 ip address 13.13.13.1 255.255.255.0
!
ip route 24.24.24.0 255.255.255.0 Tunnel0