Look up your WAN and LAN IP address and rDNS.
An IP (Internet Protocol) address is a unique number that identifies a computer or device on a network.
WAN (Wide Area Network) or Public IP address is what other devices on the internet see you as
and is the number which other PCs/servers etc will use to send and receive data to you. Your IP address is normally issued by your ISP and it can either be Static or Dynamic.
LAN (Local Area Network) address is the "Private" IP address of a machine on a localised network. Most home networks in the UK tend to use 192.168.x.x range, but IANA has reserved the following blocks, any of which may be used for a private network.
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
rDNS is short for Reverse DNS (Domain Name System/Server).
DNS is the method of looking up or resolving a Domain Name to an IP address. When our browsers request the url www.google.com then it is DNS that resolves the google domain or host name to the IP address of one of google's web servers such as 184.108.40.206 so that we can request information from the website. rDNS is looking up the hostname from the IP address.
By default most people will use their ISP DNS servers to perform this task, although you can use which ever DNS server you like.