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2.2. LAN IP Addresses

Every device on your LAN needs a LAN address, including your Raspberry Pi. If you want to find that device, you need to know what that address is.
Most home LANs use the Dynamic Host Configuration Protocol (DHCP). This protocol assigns IP addresses automatically to every device on the LAN. The router, often a wireless router, is usually given this job. Since the addresses are assigned automatically, the user typically doesn't know what those addresses will be.
There are two ways we can deal with this, but in both cases, we start by finding out what addresses our router uses. Each router can assign addresses up to the entire subnet, usually 256 addresses. However, for reasons like our current situation, most routers only assign addresses for part of the available range. Rarely will the home user need more than a dozen or so addresses.
Every router is different, but on the router's administration web page will be a section like the following:
Router DHCP address range
Router web page
Figure 4. Router DHCP address range

What we care about is the range of addresses reserved for DHCP, in the above case, 100 to 149. The router itself almost always uses 1, and 255 is a reserved address, so the possible addresses are 2 to 99 and 150 to 254. We may have assigned one or two other addresses for the router, so we should look through the router pages to see if there are others, and of course, we may have assigned addresses for something else so we need to avoid those.
We need to select two addresses not within the DHCP range and not used by something else. One of these must have the first three numbers the same, the second can be almost any address not used by something else. So, for example, we might choose for the first, and for the second. (Addresses beginning with 192.168 are slightly safer than most other numbers.)