0.0.0.0
0.0.0.0 means "this host" or "any/all addresses" depending on context — as a route it is the default route; as a bind it means all interfaces.
What it is used for
In a routing table 0.0.0.0/0 is the default route (the gateway of last resort).
Where you will see it
Understanding reserved addresses like this is core CCNA knowledge — they appear constantly in routing tables, DHCP and troubleshooting.
Frequently asked questions
What is 0.0.0.0?
0.0.0.0 means "this host" or "any/all addresses" depending on context — as a route it is the default route; as a bind it means all interfaces.
Is 0.0.0.0 routable on the internet?
No — it is a reserved special-purpose address and is not routed on the public internet.
Where is it used?
In a routing table 0.0.0.0/0 is the default route (the gateway of last resort).
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