New IOS release 15.x introduced Easy Virtual Network (EVN) functionality to leverage some existing deployment features such as VRF-Lite and QinQ.
Its ease of configuration is a real advantage. The idea is very simple: tag each VRF and trunk them to other vNET routers (PE). We will show an example of how it runs on an EIGRP deployment of CEs connecting to each other through PEs that are vNET routers.
In Figure.1, customer A (in green) interconnects two CEs: CE1-A and CE2-A through vNET router1 and router2. Customer B is represented in yellow and interconnects three sites. The configuration of participating routers is given next:
EVN introduces the concept of a vNET trunk and behave such as bundle of sub interfaces affected to each corresponding vrf (vpn) with an inherited or local IP configuration
First, each vrf is tagged with a different vNET id that ranges from 2 to 4094. Second, vNET trunks are configured toward other vNET routers that are generally PE routers.
As soon as vNET trunks are configured, sub interfaces are automatically created under vNET trunk physical interface and attached to the corresponding VRFs.
By default, these sub interfaces inherit the same IP configuration from the vNET trunk. We understand here why it is not possible to configure a vNET trunk over a sub interface!
EIGRP neighborship is established on previously created sub interfaces:
Routing information is exchanged transparently as if it was done in a VRF-Lite configuration. An example of a learned EIGRP route:
Ease of configuration is a real advantage. In contrast with VRF-Lite, EVN uses the same physical interface to bundle all vNETs. Each VRF is identified by a different vNET tag which is similar to MP-BGP where VRFs are identified by local MPLS labels.
But EVN presents many limitations :
- Number of VPNs is limited by the number of vNETs
- Number of vNETs limited by the number of available vlans at the core network or between vNET routers
- Limited scalability in growing networks in comparison with MP-BGP VPNv4 networks
- Limited handling of complex routing information redistribution scenarii in comparison with MP-BGP VPNv4 networks