Blade ICE G8124-E Manuale Utente

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  Chapter 15: Basic IP Routing

BMD00220, October 2010

For example, consider the following topology migration: 

The 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 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.

Internet

Internet

Internet

Internet

BLADE

Switch

Server
Subnet

Server
Subnet