Nortel Networks WEB OS 212777 - Manual (Page 29)

Web OS 10.0 Application Guide
Chapter 1: Basic IP Routing n 29
212777-A, February 2002
For example, consider the following topology migration:
Figure 1-1 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:
n
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.
n
Traffic to the router increases, increasing congestion.
Even if every end-station could be moved to better logical subnets (a daunting task), competi-
tion for access to common server pools on different subnets still burdens the routers.
This problem is solved by using Alteon Web switches with built-in IP routing capabilities.
Cross-subnet LAN traffic can now be routed within the Web 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.
Admin/Sales
Server
Subnet
Router
Switch
Staff/Eng2
Switch
Eng/Staff2/Sales
Switch
FDDI
Internet
Web Switch
Admin. Subnet
Server
Subnet
Hub
Staff Subnet
Hub
Eng. Subnet
Hub
Internet
FDDI Router