I have a requirement to regularly produce spreadsheet showing Cisco router interface information, in particular bandwidths of each interface and IP addresses. I have access to a network management tool which I can pull reports from so the information is there, I just need to understand it and present it logically
So one of the requirements is to show LAN and WAN side IP addresses in the spreadsheet under their own column. I understand the difference between these in a home network context – LAN side is the local IP that other devices see and the WAN side is the address that the internet sees. However in this context, I cannot seem to separate which is which..
This is what I have to work with (IPs and interface descriptions have been removed) for example for each interface
Device name, Interface Name Interface Description IP Address Speed Type
Hostname1 FastEthernet0/0/0 (Fa0/0/0) Example LAN 2 MBit/s (F) ethernetCsmacd
How do I look at the IP addresses and work out whether the IP relates to the LAN or WAN side?
Best Answer
First, it is important to understand that the exact particulars of what is LAN or WAN in any given network are subjective for that network. General LAN\WAN definitions can be conjured up but specific network designations will vary from network to network. Next, it is impossible to look solely at an IPv4 address and state for certain whether or not it belongs to the LAN or WAN. One needs to understand more about the addressing in a particular network in order to know for sure. This of course excludes the RFC1918 private IPv4 space which I personally would always consider as LAN.
Further, the delineation between LAN and WAN is not as clear as it used to be. Loosely speaking, the traditional demarcation between the two was private and public meaning the stuff "we" control (private - LAN) and stuff controlled by someone else (service provider - WAN). This delineation is still fairly correct today however the issue has been clouded somewhat by the advent of VLANs, VPLS, MPLS, MetroEthernet, etc.
Therefore, in today's vernacular, it seems safe to say that any address that is upstream and outside of your network - especially IPs that are used to directly connect your network to the Internet - are likely WAN and all other addresses within your network could safely be deemed LAN.