Netgear XSM4324FS Software Administration Manual Software Version 12.x - Page 78

M4300 Series and M4300-96X Fully Managed Switches Port Routing Concepts The first networks were small enough for the end stations to communicate directly. As networks grew, Layer 2 bridging was used to segregate traffic, a technology that worked well for unicast traffic, but had problems coping with large quantities of multicast packets. The next major development was routing, where packets were examined and redirected at Layer 3. End stations needed to know how to reach their nearest router, and the routers had to interpret the network topology so that they could forward traffic. Although bridges tended to be faster than routers, using routers allowed the network to be partitioned into logical subnetworks, which restricted multicast traffic and also facilitated the development of security mechanisms. An end station specifies the destination station's Layer 3 address in the packet's IP header, but sends the packet to the MAC address of a router. When the Layer 3 router receives the packet, it will minimally: • Look up the Layer 3 address in its address table to determine the outbound port. • Update the Layer 3 header. • Re-create the Layer 2 header. The router's IP address is often statically configured in the end station, although the switch supports protocols such as DHCP that allow the address to be assigned dynamically. Likewise, you can assign some of the entries in the routing tables used by the router statically, but protocols such as RIP and OSPF allow the tables to be created and updated dynamically as the network configuration changes. Port Routing Configuration The switch always supports Layer 2 bridging, but Layer 3 routing must be explicitly enabled, first for the switch as a whole, and then for each port that is to be part of the routed network. The configuration commands used in the example in this section enable IP routing on ports 1/0/2,1/0/3, and 1/0/5. The router ID will be set to the switch's management IP address, or to that of any active router interface if the management address is not configured. After the routing configuration commands have been issued, the following functions will be active: • IP forwarding, responsible for forwarding received IP packets. • ARP mapping, responsible for maintaining the ARP Table used to correlate IP and MAC addresses. The table contains both static entries and entries dynamically updated based on information in received ARP frames. • Routing Table Object, responsible for maintaining the common routing table used by all registered routing protocols. Port Routing 78 Software Administration Manual