IP R
OUTING
17-4
If the switch determines that a frame must be routed, the route is
calculated only during setup. Once the route has been determined, all
packets in the current flow are simply switched or forwarded across the
chosen path. This takes advantage of the high throughput and low latency
of switching by enabling the traffic to bypass the routing engine once the
path calculation has been performed.
Routing Path Management
Routing Path Management involves the determination and updating of all
the routing information required for packet forwarding, including:
• Handling routing protocols
• Updating the routing table
• Updating the Layer 3 switching database
Routing Protocols
The switch supports both static and dynamic routing.
• Static routing requires routing information to be stored in the switch
either manually or when a connection is set up by an application outside
the switch.
• Dynamic routing uses a routing protocol to exchange routing
information, calculate routing tables, and respond to changes in the
status or loading of the network.
The switch supports RIP and RIP-2 dynamic routing protocols.
RIP and RIP-2 Dynamic Routing Protocols
The RIP protocol is the most widely used routing protocol. RIP uses a
distance-vector-based approach to routing. Routes are determined on the
basis of minimizing the distance vector, or hop count, which serves as a
rough estimate of transmission cost. Each router broadcasts its
advertisement every 30 seconds, together with any updates to its routing
table. This allows all routers on the network to learn consistent tables of
next hop links which lead to relevant subnets.
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