Introduction
Cisco Layer 3 interfaces are physical or virtual network interfaces on Cisco devices, such as routers or switches, that are capable of performing Layer 3 (network layer) functions. Layer 3 interfaces are used to connect networks together and allow communication between different devices across different subnets. IP routing, on the other hand, is the process of forwarding IP packets from one network to another. IP routing is performed by routers and Layer 3 switches, which examine the destination IP address of a packet and decide how to forward it based on the routing table. The routing table contains information about the available paths that a packet can take to reach its destination, including the next hop router and the outgoing interface. When a Layer 3 interface is configured on a Cisco device, it is assigned an IP address and subnet mask that identifies the network to which it belongs. The device can then use this information to perform IP routing. For example, if a packet arrives on an interface with a destination IP address that belongs to a different network, the device will consult its routing table to determine the best path to forward the packet. This may involve sending the packet to another router or forwarding it out a different interface on the same device.
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