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Chapter 4. Port Routing | 60
4
4. Port Routing
This chapter provides the following sections:
• Port Routing Configuration on page 61
• Enable Routing for the Switch on page 62
• Enable Routing for Ports on the Switch on page 62
• Add a Default Route on page 65
• Add a Static Route on page 66
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 M4100 and
M7100 Managed 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.