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Why IP Addresses? Why private and public both IP address needed?

IP Networks use Routers to do the switching based on IP addresses, Layer 3 routing protocols like BGP or OSPF an Ethernet networks use 48 bit MAC addresses

Spanning Tree is used to route because users, base stations, routers, etc will all need IP addresses (It is an IP-based system)

There are Public (Internet routable) and Private IP addresses (not seen on the Internet) and conversion between them some users may already have public IP addresses, some will Not

An aside: IP header compression will be used throughout

Private IP Addresses

IANA, the Internet Assigned Numbers Authority, who look after these things, has designated some blocks of IP addresses for use as private IP designations.

These addresses should only be used within private LANs and must not become visible on the public Internet.

“10” Block –

“172” Block –

“192” Block –

There is also an IP block which is used for local IP number assignment when a DHCP server is not available.

This is known as Automatic Private IP Addressing.

“169” Block –

Both Public and Private IP Addresses Needed

Business users may have a network with routers, small businesses may look like residential customers

Residential Users

No IP address. Need the Network to provide one using DHCP

Business Users

May have own network and allocation of Private IP Addresses Use NAT at the edge of the network to convert to Public IP Addresses

IP Address

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