Figure 8-2:Switch-Based Routing Topology - Nortel Alteon OS 42C4911 Application Manual

Alteon OS Application Guide
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), competi-
tion for access to common server pools on different subnets still burdens the routers.
This problem is solved by using GbE Switch Modules 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.
Take a closer look at the BladeCenter's GbE Switch Module in the following configuration
example:
Figure 8-2 Switch-Based Routing Topology
The GbE Switch Module connects the Gigabit Ethernet and Fast Ethernet trunks from various
switched subnets throughout one building. Common servers are placed on another subnet
attached to the switch. A primary and backup router are attached to the switch on yet another
subnet.
146 Chapter 8: Basic IP Routing
10 Gbps
IF #2 IF #2
IF #1 IF #1
10 Gbps
Server Subnet:
IF #3 IF #3
206.30.15.2-254 206.30.15.2-254
IF #4 IF #4
GbESM
BladeCenter
BladeCenter
42C4911, January 2007