Category Archives: EVN

Easy Virtual Network

What Is the Value of 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 subinterface 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 subinterface by using “vnet trunk” command. This
helps reduce the amount provisioning across the network infrastructure as shown in
figure 1.
– 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 subinterfaces are automatically created and hidden.
– The configuration of the main interface is inherited by all (hidden) subinterfaces.
– 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.

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, as illustrated
in Figure 2

Components Used

The information in this document is based on these hardware and software versions:
Cisco Catalyst 6000 (Cat6k) Series switches that run software Version 15.0(1)SY1

Cisco 1000 Series Aggregated Services Routers (ASR1000) that run software Version 3.2s

Cisco 3925 and 3945 Series Integrated Services Routers that run Cisco IOS® Versions 15.3(2)T and later

Cisco Catalyst 4500 (Cat4500) and 4900 (Cat4900) Series switches that run software Version 15.1(1)SG


Click to access evn-overview.pdf

Click to access aag_c45-675118.pdf