Handbook

N8406-023 1Gb Intelligent L3 Switch Application Guide 92
Take a closer look at the switch in the following configuration example:
Figure 15 Switch-based routing topology
The switch 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. Primary and backup routers are
attached to the switch on yet another subnet.
Without Layer 3 IP routing on the switch, cross-subnet communication is relayed to the default gateway (in this
case, the router) for the next level of routing intelligence. The router fills in the necessary address information and
sends the data back to the switch, which then relays the packet to the proper destination subnet using Layer 2
switching.
With Layer 3 IP routing in place on the switch, routing between different IP subnets can be accomplished entirely
within the switch. This leaves the routers free to handle inbound and outbound traffic for this group of subnets.
To make implementation even easier, UDP Jumbo frame traffic is automatically fragmented to regular Ethernet
frame sizes when routing to non-Jumbo frame VLANS or subnets. This automatic frame conversion allows servers
to communicate using Jumbo frames, all transparently to the user.
Example of subnet routing
Prior to configuring, you must be connected to the switch Command Line Interface (CLI) as the administrator.
NOTE: For details about accessing and using any of the menu commands described in this example, see
the Command Reference Guide.
1. Assign an IP address (or document the existing one) for each router and client workstation.
In the example topology, the following IP addresses are used:
Table 21 Subnet routing example: IP address assignments
Subnet
Devices
IP Addresses
1
Primary and Secondary Default Routers
205.21.17.1 and 205.21.17.2
2
First Floor Client Workstations
100.20.10.2-254
3
Second Floor Client Workstations
131.15.15.2-254
4
Common Servers
206.30.15.2-254
Switch
Blade Enclosure