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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 83 Configuring Easy Virtual Network
About Easy Virtual Network
The term “VRF aware” can also be used to describe a software component running on the device. A
software component is VRF aware if it can operate on different EVNs. For example, ping is VRF aware
because it allows you to choose the EVN to which you want to send the ping packet.
Routing Protocols Supported by EVN
Each EVN runs a separate instance of a routing protocol. This allows each EVN to fine-tune its routing
separately and also limits fate sharing. Different virtual networks may run different routing protocols
concurrently.
EVN supports static routes, OSPFv2, and PIM, MSDP, and IGMP for multicast routing.
Packet Flow in a Virtual Network
Packets enter an EVN through an edge interface, traverse multiple trunk interfaces, and exit the virtual
network through another edge interface. At the ingress edge interface, packets are mapped from a VLAN
into a particular EVN. Once the packet is mapped to an EVN, it is tagged with the associated virtual
network tag. The virtual network tag allows the trunk interface to carry packets for multiple EVNs. The
packets remain tagged until they exit the EVN through the egress edge interface.
On the edge interface, the EVN associated with the interface is used for route lookup. On the trunk
interface, the virtual network tag carried in the packet is used to locate the corresponding EVN for
routing the packets.
If the egress interface is an edge interface, the packet is forwarded untagged. However, if the egress
interface is a trunk interface, the packet is forwarded with the tag of the ingress EVN.
The figure below illustrates how traffic from two VRFs, red and green, can coexist on the same IP
infrastructure, using the tags 101 and 102.
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