Routed Ports on Layer 3 Switches

Every Layer 3 switch port can be configured two ways: as a switched port (part of a VLAN, forwarding at Layer 2), or as a routed port (with its own IP, forwarding at Layer 3). Most engineers default to SVIs and forget routed ports exist. That's a shame, because routed ports are the right answer for uplinks between Layer 3 switches.

#Routed Port vs. SVI#link

The distinction matters because routed ports don't participate in STP — they're not switched. On a link between two Layer 3 switches where you want routing, a routed port is cleaner and slightly faster than an SVI. On a port facing user devices, an SVI (via VLAN membership) is what you want.

#Configuring a Routed Port#link

The `no switchport` command is the key — it converts the port from Layer 2 to Layer 3. Without it, `ip address` will be rejected on a switch port. With it, the port behaves like a router interface: no VLANs, no trunking, no STP, just IP forwarding.

#The /30 or /31 Convention#link

Point-to-point routed ports between switches are usually configured as /30 or /31 subnets. A /30 gives two usable addresses for two endpoints — exactly what you need. A /31 (RFC 3021) gives two usable addresses with a tighter mask — modern IOS supports this and it's becoming standard.

#When to Use Routed Ports#link

• ▪Uplinks between Layer 3 switches — cleaner than SVIs on a dedicated VLAN
• ▪WAN handoffs — connecting to a router that expects a routed interface
• ▪Core-facing ports — where Layer 2 features add no value
• ▪Any port that will only ever carry routed traffic

#Check Your Understanding#link