The following processes take place when the frame arrives at R3:
1. R3 copies the data link PPP frame into its buffer.
2. R3 de-encapsulates the data link PPP frame.
3. R3 searches the routing table for the destination IPv4 address of the packet. The routing table has a route to a directly connected network on R3. This means that the packet can be sent directly to the destination device and does not need to be sent to another router.
Because the exit interface is a directly connected Ethernet network, R3 must resolve the destination IPv4 address of the packet with a destination MAC address:
1. R3 searches for the destination IPv4 address of the packet in its Address Resolution Protocol (ARP) cache. If the entry is not in the ARP cache, R3 sends an ARP request out of its FastEthernet 0/0 interface. PC2 sends back an ARP reply with its MAC address. R3 then updates its ARP cache with an entry for 192.168.4.10 and the MAC address that is returned in the ARP reply.
2. The IPv4 packet is encapsulated into a new Ethernet data link frame and sent out the FastEthernet 0/0 interface of R3.
3. When PC2 receives the frame, it examines the destination MAC address, which matches the MAC address of the receiving interface, its Ethernet network interface card (NIC). PC2, therefore, copies the rest of the frame into its buffer.
4. PC2 identifies the Ethernet Type field as 0x800, which means that the Ethernet frame contains an IPv4 packet in the data portion of the frame.
5. PC2 de-encapsulates the Ethernet frame and passes the IPv4 packet to the IPv4 process of its operating system.
The animation in the figure illustrates how R3 forwards the packet to PC2.