Question on internal/external IPs

What is the generic rule to determine if an IP is internal only to a network or if it can be rerouted and pinged from outside ?

Normally internal IPs are something like 10.0.0.x or 192.168.0.x, but I'm sure these ranges are not the only ones. I assume there is an agreed upon set that can be used internally. Is it all 10.x.x.x and all 192.x.x.x ? Are there more ?

The whole thing was spawned by a friend's question whose office is using the unusual range of 192.9.200.x! Is this internal or external ?

Many thanks AK

RFC 3330 "Special-Use IPv4 Addresses" documents some of the other networks:

RFC 1918 is still alive with a status of "Best Current Practice"; it's also known as BCP0005. RFC 3330 has a status of "Informational." As you noticed, it documents networks in addition to those mentioned in RFC 1918.

On 10 Dec 2004 15:03:05 -0700, Michael Fuhr spoketh

Wow, they're up to 3330 now? Last I checked, it was 1918.

Now that I'm reading it, the difference is that 3330 mentions all "special use" addresses, while 1918 only mentions the three ranges that have been set aside for private networks.

Lars M. Hansen

AnalogKid wrote in news: snipped-for-privacy@4ax.com:

By convention, these are the normal ranges, but I believe that you can use any address you want as long as you don't route them and are willing to accept that you will not be able to access any outside addresses that match what you are using. This, I think, is the main point for using the conventional addresses as they will not be assigned as valid internet addresses and therefore, you are not blocking any real addresses.

At least, that is my understanding.

David Wright

Private IP Address Ranges Class From To CIDR Mask Decimal Mask Class "A" or 24 Bit 10.0.0.0 10.255.255.255/8 255.0.0.0

Class "B" or 20 Bit 172.16.0.0 172.31.255.255/12 or /16 255.240.0.0 or 255.255.0.0

Class "C" or 16 Bit 192.168.0.0 192.168.255.255/16 or /24 255.255.0.0 or 255.255.255.0