Keep example addresses off the public Internet
03A reservation describes how addresses should be used. Operators still need an actual routing or filtering policy.
SHOULD NOT appear publicly; SHOULD list as non-routeable; if filters are deployed, SHOULD include these blocks. The RFC does not say universal MUST filtering.
Source for this drawing: RFC 5737 · Read RFC section 4 ↗
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.
RFC 5737 recommends keeping TEST-NET addresses off the public Internet.
- Addresses in these blocks SHOULD NOT appear on the public Internet.
- Operators SHOULD add these blocks to non-routeable address lists. If packet filters are deployed, the blocks SHOULD be added to them.
- A reservation is not an automatic firewall. The illustrated filter is a chosen configuration, not a guarantee about every network.
Examples are documentation text, not a network configuration. No packets are sent. SHOULD and SHOULD NOT are recommendations, not MUST. Valid exceptions require understanding and carefully weighing the full implications (RFC 2119 §§3–4).
Read the RFC section ↗