Cisco Systems IE 2000 IP Routing

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Cisco IE 2000 Switch Software Configuration Guide
OL-25866-01
Chapter 41 Configuring Static IP Unicast Routing
IP Routing
IP Routing
In some network environments, VLANs are associated with individual networks or subnetworks. In an
IP network, each subnetwork is mapped to an individual VLAN. Configuring VLANs helps control the
size of the broadcast domain and keeps local traffic local. However, network devices in different VLANs
cannot communicate with one another without a Layer 3 device to route traffic between the VLA Ns,
referred to as inter-VLAN routing. You configure one or more routers to route traffic to the appropriate
destination VLAN.
Figure 41-1 shows a basic routing topology. Switch A is in VLAN 10, and Switch B is in VLAN 20. The
router has an interface in each VLAN.
Figure 41-1 Routing Topology Example
When Host A in VLAN 10 needs to communicate with Host B in VLAN 10, it sends a packet addressed
to that host. Switch A forwards the packet directly to Host B, without sending it to the router.
When Host A sends a packet to Host C in VLAN 20, Switch A forwards the packet to the router, which
receives the traffic on the VLAN 10 interface. The router uses the routing table to finds the correct
outgoing interface, and forwards the packet on the VLAN 20 interface to Switch B. Switch B receives
the packet and forwards it to Host C.
When static routing is enabled on Switch A and B, the router device is no longer needed to route packets.
Types of Routing
Routers and Layer 3 switches can route packets in these ways:
• Using default routing to send traffic with a destination unknown to the router to a default outlet
or destination
• Using static routes to forward packets from predetermined ports through a si ngle path into and out
of a network
• Dynamically calculating routes by using a routing protocol
The switch supports static routes and default routes. It does not support routing protocols.
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A
B
C
Host
Host
Host
Switch A Switch B
VLAN 10 VLAN 20
ISL Trunks