Implementing IBM System Networking 10Gb Ethernet Switches

60 Implementing IBM System Networking 10Gb Ethernet Switches

2.3 IP routing

IBM System Networking switches use a combination of configurable IP switch interfaces and

IP routing options. The switch IP routing capabilities provide the following benefits:

򐂰 Connects the server IP subnets to the rest of the backbone network.

򐂰 Provides routing of IP traffic between multiple VLANs configured on the switch.

The physical layout of most corporate networks has evolved over time. Classic hub/router

topologies have given way to faster switched topologies, particularly now that switches are

increasingly intelligent. IBM System Networking switches are intelligent and fast enough to

perform routing functions on a par with wirespeed Layer 2 switching. The combination of

faster routing and switching in a single device provides another service: You can build

versatile topologies that account for earlier configurations.

Figure 2-7 shows a corporate campus migrated from a router-centric topology to a faster,

more powerful, switch-based topology. As often the case is, network growth and redesign has

left the system with a mix of illogically distributed subnets.

Figure 2-7 Router-centric versus switch-based network topologies

This situation in one 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 endpoint 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. Because IBM

System Networking switches use ASIC for forwarding Layer 3 packets, cross-subnet LAN

traffic can now be routed within the switches with wirespeed Layer 2 switching performance.

This configuration eases not only the load on the router, but saves the network administrators

from reconfiguring each endpoint with new IP addresses.