Why is my router's WAN IP different from public IP?

Related questions

1. Why is IPv4 32 bit?
2. Is IPv6 faster than IPv4?
3. Is IPv6 better than IPv4?
4. What is WAN IP and LAN IP?
5. Whats is my static IP?
6. How is a WAN created?
7. Is IPv6 better than IPv4 for gaming?
8. Can 255 be used in an IP address?
9. What are WAN settings?
10. Why do we use IPv4?

Tags

1. #upstream
2. #using
3. #cause
4. #their
5. #service
6. #assigned
7. #either
8. #different
9. #connection
10. #internet
11. #proxy
12. #interface
13. #router
14. #doing
15. #computer
16. #basically