How do you configure an SVI (Switch Virtual Interface) with IPv4/IPv6 addresses and a default gateway on a Cisco switch?

Enter the VLAN (Virtual Local Area Network) interface, assign the IPv4/IPv6 addresses, no shutdown it, then set the default gateway in global config.

Step 1: Configure the Management Interface

S1# configure terminal
S1(config)# interface vlan 99
S1(config-if)# ip address 172.17.99.11 255.255.255.0
S1(config-if)# ipv6 address 2001:db8:acad:99::1/64
S1(config-if)# no shutdown
S1(config-if)# end
S1# copy running-config startup-config

Step 2: Configure the Default Gateway

S1# configure terminal
S1(config)# ip default-gateway 172.17.99.1
S1(config)# end
S1# copy running-config startup-config

Key notes:

• The switch does not need an IPv6 default gateway — it learns it automatically via RA (Router Advertisement) messages
• For IPv6 on older Catalyst 2960 switches (IOS 15.0), first run: sdm prefer dual-ipv4-and-ipv6 default then reload
• Always copy running-config startup-config to persist changes across reboots

Go deeper:

• Default gateway (Wikipedia) — why a L2 switch needs a gateway to reach managers on other subnets.
• Neighbor Discovery Protocol (Wikipedia) — the Router Advertisement mechanism that lets the switch learn its IPv6 gateway automatically.