What is VRF and VRF Lite?

The VRF full form in networking is Virtual Routing and Forwarding.  The routers do the routing using a table. But what is Virtual Routing or VRF? It is similar to the IP routing, but unlike the normal router, a router with VRF technology may have multiple routing tables to separate the IP traffic. It looks similar to the VLAN but works on layer 3.  This brings virtualization of the routers.  Feels that all segmented traffic has its own dedicated routers. But the difference is that in VRF there can be only one routing table, while a router may have multiple.

By isolating network traffic,  a service provider can provide a VPN to its customers.  This brings fewer requirements for authentication and encryption.

Default IP Routing?

Routing is the process for transmitting data from one host to another. The communicating hosts may be in the same or different networks. Data have an IP header with source and destination IP addresses.  When a host needs to send data out, it sends a packet to the router. At the host, the router address is configured as the default gateway.

Once gets a packer, the router looks into the global routing table and forwards the packet to the next hope. Routing using a global routing table is named default routing.

Why we need separation of IP traffic?

We need separation of entities in many cases.  Suppose there are multiple departments in a company and we do not want to expose any resource from one department to another.  The option is simple, limit communication within a department.  By restricting access, the HR department can not have access to marketing servers or files.

Why we need VRF if there is a VLAN option?

The way they work answers.  VLAN works at layer two while VRF is at layer 3.   If there are multiple VLANs in the company, over the switches.  All switches connected to the router for external network access.  This brings a problem, a host in VLAN can access another host in another VLAN.  If we have VRF, the a host can access hosts in the same VRF.

Using VRF, an ISP can provide isolation of IP traffic between distance hosts.   The ISP will configure VRF on each router between the path.

Virtual Routing Tables in VRF:

These are similar to the normal routing tables associated with an interface.  If a message comes on the interface if checks for routing in the VRF table only.