As defined in the "Network Technology Basics" module of the HCIA-Cloud Computing training, a router is a Layer 3 (Network Layer) device responsible for interconnecting different network segments and selecting the optimal path for data packets. To perform this function, the router maintains and manages a Routing Table. This table is the "map" of the network that the router uses to make forwarding decisions. Every entry in the routing table typically includes several key parameters: the destination network address, the subnet mask, the protocol (how the route was learned, such as Static, OSPF, or BGP), the preference value, the cost (metric), and the next-hop address or outbound interface.
When a router receives an IP packet, it examines the destination IP address and performs a lookup in its routing table to find the most specific match (longest match rule). If a matching entry is found, the router encapsulates the packet into a new frame and sends it toward the next hop. If no match is found and no default route exists, the packet is discarded. This process is fundamental to the operation of a Cloud Data Center where multiple Virtual Private Clouds (VPCs) and subnets must communicate through virtual or physical routers.
While a switch manages a MAC address table to forward frames at Layer 2, and a host manages an ARP table to map IP addresses to MAC addresses, only the routing table provides the cross-network path intelligence required for routing. In Huawei’s virtualization solutions, virtual routers within the software-defined networking (SDN) layer use these same logic principles to ensure that traffic between virtual machines in different subnets is directed efficiently to the correct destination. Proper management of the routing table is therefore the cornerstone of network reachability in cloud environments.
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