The logical properties of an interface are the characteristics that do not apply to the physical interface or the wires connected to it. Logical properties include the protocol families running on the interface (including any protocol-specific MTUs), the IP address or addresses associated with the interface, virtual LAN (VLAN) tagging, and any firewall filters or routing policies that are operating on the interface.
The IP specification requires a unique address on every interface of each system attached to an IP network, so that traffic can be correctly routed. Individual hosts such as home computers must have a single IP address assigned. Routers must have a unique IP address for every interface.
This section contains the following topics: