Hi there, everybody!
This post explains what is vpn-instance on AR and NE routers. Please see more details as you read below.
BACKGROUND INFORMATION
As we know, in MPLS network quite a few users which is called CE(customer edge) access to ISP which is called PE(provider edge), here is the problem, if each CE access to the PE with the physical interface, patently, there wouldn't be enough interfaces on PE. Some guys maybe say this problem could be solved by using sub-interface, yes, sub-interface could solve this problem, but there is another problem that we can't ignore, the problem is how to distinguish the routes for the different users. Here we put the vrf also called vpn-instance forward.
On wiki VRF is described as: In IP-based computer networks, virtual routing and forwarding (VRF) is a technology that allows multiple instances of a routing table to co-exist within the same router at the same time. Because the routing instances are independent, the same or overlapping IP addresses can be used without conflicting with each other. Network functionality is improved because network paths can be segmented without requiring multiple routers. It seems hard to understand.
In fact, we can regard VRF as virtual router, just like divide the physical router into a lot of virtual routers, each virtual router represents a vrf. just as the picture below shows:
ROUTE PROTOCOLS
Let's talk about the route protocols implemented on the router which has enabled the vpn-instance.
It's known that more than one OSPF process and only one BGP process can be implemented on the router simultaneously. If we enable one OSPF process on the router and import the routes which belong to the vpn-instance, will it success? In fact, this is invalid. We should enable OSPF process for each vpn-instance, and routing-table for each OSPF process are independent. The same action should be performed for other route protocols, but not for the BGP. Actually, we can only enable one BGP process on a router, so the BGP on the router will contain all of the routes comes from the vpn-instance. In this secnario, it feels like the figure below:
This would be all on what is vpn-instance on AR and NE routers. Thanks for reading this post!
