VRFs: separation without separate hardware

A VRF gives a router more than one routing table. Interfaces are assigned to a VRF, and traffic in one VRF cannot reach another unless you deliberately build a path between them. It is genuine separation on shared hardware.

What it is good for

Keeping traffic classes apart end to end. Voice and data. Corporate and guest. Production and building management. Each gets its own table, its own routes, and its own default. Overlapping address space becomes possible: two customers can both use 10.0.0.0/8 without conflict, because the tables never meet.

It is also a strong security boundary. Not a filter that can be misconfigured to permit traffic, but an absence of any route at all. There is nothing to permit.

What it costs

Everything becomes VRF-aware, and forgetting that is the main source of trouble. A ping from the router uses the global table unless told otherwise. So does a traceroute, an SNMP poll, an NTP query, a TFTP transfer, and a routing protocol instance.

ping vrf DATA 10.1.1.1
show ip route vrf VOICE
traceroute vrf DATA 10.1.1.1

Management traffic needs a decision: a dedicated management VRF is the clean approach, and it means a mistake in a user VRF cannot cut your access to the device.

Connecting VRFs when you must

Route leaking with route targets, or a physical or logical link between them. Both are deliberate acts, which is the point — you cannot leak by accident.

The practical warning

The most common VRF incident is an engineer troubleshooting in the wrong table: pinging successfully from the global table and concluding the VRF works. Always state which VRF you are testing, in the command and in the ticket. “It pings” is not a complete sentence on a router with VRFs.