VLANCCNA 200-301

Layer 3 Switch SVI Interface Not Coming Up

Presenting Symptom

A host connected to an access switch cannot ping the default gateway IP address configured on a Layer 3 switch SVI, and the SVI interface shows as administratively down.

Network Context

A small branch office network uses a Cisco Catalyst 3560-X Layer 3 switch as the distribution layer, running IOS 15.0. The switch has VLAN 10 configured for the user subnet 192.168.10.0/24. The SVI for VLAN 10 (interface Vlan10) has IP address 192.168.10.1/24 configured. The switch has been recently reconfigured, and the SVI is not coming up.

Diagnostic Steps

Check SVI status

show interfaces vlan 10

Vlan10 is administratively down, line protocol is down

The SVI is administratively down. This indicates the interface has been manually shut down or the VLAN is not created in the VLAN database.

Verify VLAN exists

show vlan brief

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Gi0/1, Gi0/2
10   VLAN0010                         active    Gi0/3, Gi0/4
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup

VLAN 10 is present and active. If VLAN 10 were missing, the SVI would not be created. Since VLAN exists, the issue is likely the SVI being shut down.

Check SVI configuration for shutdown

show running-config interface vlan 10

interface Vlan10
 ip address 192.168.10.1 255.255.255.0
 shutdown

The 'shutdown' command is present under the SVI. This confirms the SVI is administratively down due to manual configuration.

Verify no other issues (optional)

show ip interface brief vlan 10

Interface              IP-Address      OK? Method Status                Protocol
Vlan10                 192.168.10.1    YES manual administratively down down

Confirms the SVI is administratively down. No other issues like missing VLAN or IP address misconfiguration.

Root Cause

The SVI interface Vlan10 has been manually shut down with the 'shutdown' command under the interface configuration. This is a common misconfiguration when an administrator intends to disable the SVI temporarily but forgets to re-enable it.

Resolution

Re-enable the SVI by removing the shutdown command: configure terminal interface vlan 10 no shutdown end This brings the SVI up, allowing it to act as the default gateway for VLAN 10 hosts.

Verification

Run 'show interfaces vlan 10' and 'show ip interface brief vlan 10': Vlan10 is up, line protocol is up Interface IP-Address OK? Method Status Protocol Vlan10 192.168.10.1 YES manual up up Also verify connectivity: ping from a host in VLAN 10 to 192.168.10.1 should succeed.

Prevention

["Always use 'no shutdown' when creating an SVI to ensure it is enabled by default.","Implement configuration management and change control to avoid accidental shutdowns.","Use 'show running-config interface vlan <vlan-id>' to verify SVI configuration before troubleshooting connectivity."]

CCNA Exam Relevance

On the CCNA 200-301 exam, this scenario tests understanding of Layer 3 switching and SVI operation. Questions may present a troubleshooting scenario where a host cannot reach its default gateway, and candidates must identify that the SVI is administratively down. The exam may use multiple-choice or drag-and-drop formats to select the correct show command and interpretation.

Exam Tips

Remember that an SVI must be in 'up/up' state to forward traffic; 'administratively down' indicates a shutdown command.

The 'show interfaces vlan <id>' command is the primary tool to check SVI status.

Know that 'no shutdown' is required under the SVI, not just the physical ports.

Commands Used in This Scenario

show vlan brief

Displays a summary of all VLANs configured on the switch, including VLAN ID, name, status, and ports, used to quickly verify VLAN configuration and port assignments.

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