> At first I thought of using the blocks of RFC1918, but this IPs are well known and can cause a false impression on the end user. Not just a false impression; if they show up in traceroutes they can be extremely misleading. Has anyone considered (mis)using 100.64.0.0/10 (RFC6598) for this sort of purpose? ... >> Finally we are thinking of using the blocks that I will present below, as they are little known and not routed worldwide. >> >> 198.18.0.0/15 >> 192.0.0.0/24 >> 192.0.2.0/24 >> 192.88.99.0/24 >> 198.51.100.0/24 >> 203.0.113.0/24 >> >> What do you think about this? A very bad idea. They are all reserved for a reason, and some of them are well known. 192.88.99.0/24 would a particularly dangerous choice (see RFC7526). The RIRs make it clear that none of these should be used, e.g. APNIC: Internet Assigned Numbers Authority SPECIAL-IPV4-REGISTRY-IANA-RESERVED (NET-192-0-0-0-1) 192.0.0.0 - 192.0.0.255 Internet Assigned Numbers Authority DS-LITE-RFC-6333-11-IANA-RESERVED (NET-192-0-0-0-2) 192.0.0.0 - 192.0.0.7 NetName: 6TO4-RELAY-ANYCAST-IANA-RESERVED NetHandle: NET-192-88-99-0-1 Parent: NET192 (NET-192-0-0-0-0) NetType: IANA Special Use Comment: Addresses starting with "198.18." or "198.19." are set aside for use in isolated laboratory networks used for benchmarking and performance testing. They should never appear on the Internet and if you see Internet traffic using these addresses, they are being used without permission. Comment: Addresses starting with "192.0.2.", "198.51.100.", or "203.0.113." are reserved for use in documentation and sample configurations. They should never be used in a live network configuration. No one has permission to use these addresses on the Internet.