A Gentle Introduction to Routing

“Before we get into the details, a clarification. When you hear
people refer to “non-routable addresses,” they are talking about
RFC 1918 IP addresses, i.e. private addresses. Despite the
misleading label, they certainly are routable. You can and should
have some 10.x.x.x networks for local access and management. They
can even be co-mingled with your real routers. They are called
“non-routable” because the Internet routers will drop
them. You should drop these packets at your border, as was pointed
out in this Border Security article last year. This is a point of
confusion for a lot of people.”

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