Inter-VLAN Routing using Layer 3 Switches

Layer 3 Switch Configuration

Complete the following steps to configure S1 with VLANs and trunking:

Step 1. Create the VLANs.

Step 2. Create the SVI VLAN interfaces.

Step 3. Configure access ports.

Step 4. Enable IP routing.

First, create the two VLANs as shown in the output.

D1(config)# vlan 10
D1(config-vlan)# name LAN10
D1(config-vlan)# vlan 20
D1(config-vlan)# name LAN20
D1(config-vlan)# exit
D1(config)#

2. Create the SVI VLAN interfaces.

Configure the SVI for VLANs 10 and 20. The IP addresses that are configured will serve as the default gateways to the hosts in the respective VLANs. Notice the informational messages showing the line protocol on both SVIs changed to up.

D1(config)# interface vlan 10
D1(config-if)# description Default Gateway SVI for 192.168.10.0/24
D1(config-if)# ip add 192.168.10.1 255.255.255.0
D1(config-if)# no shut
D1(config-if)# exit
D1(config)#
D1(config)# int vlan 20
D1(config-if)# description Default Gateway SVI for 192.168.20.0/24
D1(config-if)# ip add 192.168.20.1 255.255.255.0
D1(config-if)# no shut
D1(config-if)# exit
D1(config)#
*Sep 17 13:52:16.053: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan10, changed state to up
*Sep 17 13:52:16.160: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan20, changed state to up

3. Configure access ports.

Next, configure the access ports connecting to the hosts and assign them to their respective VLANs.

D1(config)# interface GigabitEthernet1/0/6
D1(config-if)# description Access port to PC1
D1(config-if)# switchport mode access
D1(config-if)# switchport access vlan 10
D1(config-if)# exit
D1(config)#
D1(config)# interface GigabitEthernet1/0/18
D1(config-if)# description Access port to PC2
D1(config-if)# switchport mode access
D1(config-if)# switchport access vlan 20
D1(config-if)# exit

4. Enable IP routing.

Finally, enable IPv4 routing with the ip routing global configuration command to allow traffic to be exchanged between VLANs 10 and 20. This command must be configured to enable inter-VAN routing on a Layer 3 switch for IPv4.

D1(config)# ip routing
D1(config)#

Routing on a Layer 3 Switch

If VLANs are to be reachable by other Layer 3 devices, then they must be advertised using static or dynamic routing. To enable routing on a Layer 3 switch, a routed port must be configured.

A routed port is created on a Layer 3 switch by disabling the switchport feature on a Layer 2 port that is connected to another Layer 3 device. Specifically, configuring the no switchport interface configuration command on a Layer 2 port converts it into a Layer 3 interface. Then the interface can be configured with an IPv4 configuration to connect to a router or another Layer 3 switch.

Routing Configuration on a Layer 3 Switch

Complete the following steps to configure D1 to route with R1:

Step 1. Configure the routed port.

Step 2. Enable routing.

Step 3. Configure routing.

Step 4. Verify routing.

Step 5. Verify connectivity.

1. Configure the routed port.

Configure G1/0/1 to be a routed port, assign it an IPv4 address, and enable it.

D1(config)# interface GigabitEthernet1/0/1
D1(config-if)# description routed Port Link to R1
D1(config-if)# no switchport
D1(config-if)# ip address 10.10.10.2 255.255.255.0
D1(config-if)# no shut
D1(config-if)# exit
D1(config)#

3. Configure routing.

Configure the OSPF routing protocol to advertise the VLAN 10 and VLAN 20 networks, along with the network that is connected to R1. Notice the message informing you that an adjacency has been established with R1.

D1(config)# router ospf 10
D1(config-router)# network 192.168.10.0 0.0.0.255 area 0
D1(config-router)# network 192.168.20.0 0.0.0.255 area 0
D1(config-router)# network 10.10.10.0 0.0.0.3 area 0
D1(config-router)# ^Z
D1#
*Sep 17 13:52:51.163: %OSPF-5-ADJCHG: Process 10, Nbr 10.20.20.1 on GigabitEthernet1/0/1 from LOADING to FULL, Loading Done
D1#

4. Verify routing.

Verify the routing table on D1. Notice that D1 now has a route to the 10.20.20.0/24 network.

D1# show ip route | begin Gateway
Gateway of last resort is not set
      10.0.0.0/8 is variably subnetted, 3 subnets, 3 masks
C        10.10.10.0/30 is directly connected, GigabitEthernet1/0/1
L        10.10.10.2/32 is directly connected, GigabitEthernet1/0/1
O        10.10.20.0/24 [110/2] via 10.10.10.1, 00:00:06, GigabitEthernet1/0/1
      192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.10.0/24 is directly connected, Vlan10
L        192.168.10.1/32 is directly connected, Vlan10
      192.168.20.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.20.0/24 is directly connected, Vlan20
L        192.168.20.1/32 is directly connected, Vlan20
D1#

5. Verify connectivity.

At this time, PC1 and PC2 are able to ping the server connected to R1.

C:\Users\PC1> ping 10.20.20.254
Pinging 10.20.20.254 with 32 bytes of data: 
Request timed out.
Reply from 10.20.20.254: bytes=32 time<1ms TTL=127
Reply from 10.20.20.254: bytes=32 time<1ms TTL=127
Reply from 10.20.20.254: bytes=32 time<1ms TTL=127
Ping statistics for 10.20.20.254:
    Packets: Sent = 4, Received = 3, Lost = 1 (25% loss).
Approximate round trip times in milli-seconds: 
    Minimum = 1ms, Maximum = 2ms, Average = 1ms 
C:\Users\PC1>
!==================================================
C:\Users\PC2> ping 10.20.20.254
Pinging 10.20.20.254 with 32 bytes of data: 
Reply from 10.20.20.254: bytes=32 time<1ms TTL=127
Reply from 10.20.20.254: bytes=32 time<1ms TTL=127
Reply from 10.20.20.254: bytes=32 time<1ms TTL=127
Reply from 10.20.20.254: bytes=32 time<1ms TTL=127
Ping statistics for 10.20.20.254:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss).
Approximate round trip times in milli-seconds: 
    Minimum = 1ms, Maximum = 2ms, Average = 1ms
C:\Users\PC2>

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