cisco ccna topics

cisco ccna topics.1.4.6 Inter-subnet IP Packet RoutingThe previous section described the mechanisms for IP communication between hosts within the same subnet. This section will analyze how IP devices communicate with each other across multiple subnets. As described in the previous section, each subnet is separated from each other by a Layer 3 device (e.g., a router). In the network shown in Figure 1-56, Hosts A and B belong to separate subnets, and Hosts A and C belong to the same subnet. Routers Rl and R2 support Layer 3 connectivity between Hosts A, C, and Host B. R3 acts as the egress gateway for those three hosts to the rest of the network. The table in the lower right corner of the figure lists the IP addresses of the relevant router interfaces and hosts.Before sending an IP packet, Host A needs to determine whether the IP address of the destination host belongs to the same IP subnet as the local IP address. The logic for sending IP packets from a host is very simple.If the IP address of the destination host belongs to the same subnet as the IP address of the local NIC, the IP packet will be delivered directly to the destination host.If the IP address of the destination host is on a different subnet from the IP address of the local NIC, the IP packet is sent to the IP address of the default gateway.The host's default gateway is a router (for example, R1 and R2 in Figure 1-56), whose function is to allow IP packets originating from or destined for a remote network to enter and exit the local IP subnet on which the host resides. The host forwards IP packets based on the local routing table. In Host A's routing table, there is a direct route with a destination network of 10.0.1.1/24 and a default route that is used to direct all packets whose destination IP address does not match the direct route to the IP address of the default gateway.X.......Figure 1-56 Example Network Consisting of 3 Routers61 Chapter 1 Network Protocols and Network Device Basicsf Portuguese