Choose the scope a host needs
01An enterprise here means a network operator that controls its own address plan. Private addresses identify hosts within that enterprise, not a globally unique Internet destination.
A host moving to the RFC’s public category needs an assigned globally unambiguous address and appropriate routing; private numbering is not global numbering.
Source for this drawing: RFC 1918 · Read RFC section 2 ↗
New to this? Start hereA quick picture + helpful background
A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
Choose connectivity needs before choosing addresses.
- RFC 1918 groups hosts into internal-only hosts, hosts using limited outside services via mediating gateways, and hosts needing direct network-layer connectivity outside the enterprise.
- The first two categories may use private addresses. Private hosts can communicate with both private and public hosts within the enterprise. Mediating gateways can provide indirect access to outside services.
- Hosts requiring the RFC’s direct outside IP connectivity need globally unambiguous addresses. A globally unique address alone does not guarantee Internet-wide connectivity; routing and operational arrangements still matter.
These are the RFC’s addressing categories, not permanent device types. The mediating gateway is a separate application exchange, not a private-source packet magically forwarded onto the Internet. RFC 1918 does not specify NAT or grant firewall protection. All names and internal addresses are fictional examples; no packets are sent.
Read the RFC section ↗