Logical Layer 3 Vlan Interfaces; Physical Layer 3 Interfaces - Cisco 4500M Software Manual

Overview of Layer 3 Interfaces

Logical Layer 3 VLAN Interfaces

The logical Layer 3 VLAN interfaces provide logical routing interfaces to VLANs on Layer 2 switches.
A traditional network requires a physical interface from a router to a switch to perform inter-VLAN
routing. The Catalyst 4500 series switch supports inter-VLAN routing by integrating the routing and
bridging functions on a single Catalyst 4500 series switch.
Figure 23-1
network are performed logically on one Catalyst 4500 series switch.
Figure 23-1 Logical Layer 3 VLAN Interfaces for the Catalyst 4500 Series Switch
Interface Ethernet
VLAN1

Physical Layer 3 Interfaces

The physical Layer 3 interfaces support capabilities equivalent to a traditional router. These Layer 3
interfaces provide hosts with physical routing interfaces to a Catalyst 4500 series switch.
Figure 23-2
Figure 23-2 Physical Layer 3 Interfaces for the Catalyst 4500 Series Switch
Interface Ethernet
Software Configuration Guide—Release 12.2(25)EW
23-2
shows how the routing and bridging functions in the three physical devices of the traditional
Router
Interface Ethernet
1.1.1.1 2.1.1.1
L2 Switch L2 Switch
VLAN2
Host 1 Host 2
Traditional network topology for routing
between VLANS
shows how the Catalyst 4500 series switch functions as a traditional router.
Router
1.1.1.1
2/1
Host 1
Physical Inter-VLAN Routing on a Catalyst 4500 series switch
Interface VLAN1
1.1.1.1
VLAN1
Host 1
Logical Inter-VLAN routing on a single
Catalyst 4500 series switch
Interface Ethernet
2.1.1.1
2/2
Host 2
Chapter 23 Configuring Layer 3 Interfaces
Routing
Interface VLAN2
2.1.1.1
VLAN2
Host 2
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