Hello Wes,
It really depends on the configuration of your interfaces. Since it’s routing for multiple VLANs, your config probably looks similar to this:
Switch(config)#interface GigabitEthernet 0/1
Switch(config-if)#description DESKTOPS
Switch(config-if)#switchport access vlan 10
Switch(config)#interface GigabitEthernet 0/2
Switch(config-if)#description SERVERS
Switch(config-if)#switchport access vlan 20
Switch(config)#interface vlan 10
Switch(config-if)#description DESKTOPS
Switch(config-if)#ip address 192.168.10.254 255.255.255.0
Switch(config)#interface vlan 20
Switch(config-if)#description SERVERS
Switch(config-if)#ip address 192.168.10.254 255.255.255.0
Your switch ports are in different VLANs and you have an SVI interface with an IP address for each VLAN.
Let’s say you are connected to AT&T with a routed port, something like this:
Switch(config)#interface GigabitEthernet 0/3
Switch(config-if)#no switchport
Switch(config-if)#description AT&T
Switch(config-if)#ip address 1.2.3.4 255.255.255.252
Switch(config-if)#ip address 1.2.3.4 255.255.255.0
As an L3 switch (with IP routing enabled), it will route between these subnets:
Switch#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is not set
1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 1.2.3.0/24 is directly connected, GigabitEthernet0/3
L 1.2.3.4/32 is directly connected, GigabitEthernet0/3
192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.10.0/24 is directly connected, Vlan10
L 192.168.10.254/32 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 192.168.20.254/32 is directly connected, Vlan20
So if an IP packet entered the AT&T interface with destination 192.168.20.100, it would get routed out of the VLAN20 interface. The switch then checks its ARP table to figure out if it knows where 192.168.20.100 is, learns the MAC address, then switches it out of one of the switch ports.
I hope this helps!
Rene