Basic IP routing 88
Figure 14 Router legacy network
In this example, a corporate campus has migrated from a router-centric topology to a faster, more powerful, switch-
based topology. As is often the case, the legacy of network growth and redesign has left the system with a mix of
illogically distributed subnets.
This is a situation that switching alone cannot cure. Instead, the router is flooded with cross-subnet communication.
This compromises efficiency in two ways:
• Routers can be slower than switches. The cross-subnet side trip from the switch to the router and back again
adds two hops for the data, slowing throughput considerably.
• Traffic to the router increases, increasing congestion.
Even if every end-station could be moved to better logical subnets (a daunting task), competition for access to
common server pools on different subnets still burdens the routers.
This problem is solved by using GbE2c switches with built-in IP routing capabilities. Cross-subnet LAN traffic can now
be routed within the switches with wire speed Layer 2 switching performance. This not only eases the load on the
router but saves the network administrators from reconfiguring each and every end-station with new IP addresses.
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