non-routable IP address [closed]

According to Wikipedia article on reserved addresses, there are 3 test networks intended for use in documentation only.

192.0.2.0/24
198.51.100.0/24
203.0.113.0/24

Any address in one of those ranges (eg 203.0.113.1) should not map to anything, and indeed should fail to route.

Depending on the type of test you are doing, there are other listed addresses and address ranges that could be appropriate for what you are trying to do.

I think you may want to reword your question. The private address segments (10.0.0.0 - 10.255.255.255, 172.16.0.0 - 172.31.255.255, 192.168.0.0 - 192.168.255.255) are commonly referred to as "non-routable" addresses. I think what you are asking for is a reserved IP address that is reserved specifically to never be assigned. As far as I know there is no address that is reserved in this fashion.