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Introduction to Cisco Easy Virtual Network ( EVN)


Easy Virtual Network (EVN) is an IP-based network virtualization solution that helps enable network administrators to provide traffic separation and path isolation on a shared network infrastructure. EVN uses existing Virtual Route Forwarding (VRF)-Lite technology to:
  • Simplify Layer 3 network virtualization
  • Improve shared services support
  • Enhance management, troubleshooting, and usability
What Problems Does It Help Solve?
EVN reduces network virtualization configuration significantly across the entire network infrastructure with the Virtual Network Trunk. The traditional VRF-Lite solution requires creating one sub interface per VRF on all switches and routers involved in the data path, creating a lot of burden in configuration management.

EVN removes the need of per VRF sub interface by using “vnet trunk” command. This helps reduce the amount provisioning across the network infrastructure

EVN enhances network virtualization troubleshooting by making VRF-Lite easier to deploy, operate, and scale. A routing context command mode allows network operators to perform troubleshooting issues that pertain specifically within a VRF without specifying the VRF name in every command.

Fig 1.1-Easy Virtual Network (EVN)

Router NB# routing-context vrf red
Router NB#
Router NB# show ip route # routing table output for VRF red
Router NB# ping 10.1.1.1 # Ping result using VRF red
Router NB# telnet 10.1.1.1 # Telnet to 10.1.1.1 in VRF red
Router NB# traceroute 10.1.1.1 # Traceroute output in VRF red

EVN improves shared services support with route replication. Multiple EVN users may require common sets of services such as Internet connectivity, email, video, Dynamic Host Configuration Protocol (DHCP), or Domain Name System (DNS).

Traditionally, sharing common services can be achieved through importing and exporting routes between virtual networks using Border Gateway Protocol (BGP), which is complex. EVN’s route replication feature allows each virtual network to have direct access to the Routing Information Base (RIB) in each VRF, allowing the ability to:
  • Link routes from a Shared VRF to several segmented VRFs but still maintain separation where it is required
  • Remove dependency on the BGP route target and route distinguisher, simplifying both configuration and complexity of importing and exporting routes
  • Remove duplicate routing tables or routes, saving memory and CPU

Features of EVN:
  • The EVN feature uses VRF-Lite in order to create several (up to 32) routing contexts.
  • The connectivity within the Virtual Routing and Forwarding (VRF) between Layer3 devices is ensured via Virtual Network (VNET) trunks.
  • The VNET trunks are regular dot1q trunks.
  • Each VRF that must be transported across the VNET trunks should be configured with a VNET tag.
  • Each VNET tag equals a dot1q tag.
  • The dot1q sub interfaces are automatically created and hidden.
  • The configuration of the main interface is inherited by all (hidden) sub interfaces.
  • Separate instances of routing protocols should be used in each VRF over the VNET trunks in order to advertise prefix reachability.
  • Dynamic route leaking between VRFs (opposed to static routes) is allowed without the use of Border Gateway Protocol (BGP).
  • The feature is supported for IPv4 and IPv6.