Cisco Cisco IOS Software Release 12.2(14)S

When a router receives a packet, the packet is mapped to a global table by default. When the ip vrf 
forwarding command is used to assign a specific VRF on the ingress interface, the packet is mapped to 
that VRF. The packet is forwarded based on the routes in the VRF.

The VRF-Autoclassify feature enables the capability to map packets from connected hosts to VRFs that 
are different from the VRF defined on the ingress interface. This feature also enables the configuration 
of policies that are required for the mapping of packets to the VRFs depending on whether the source 
address of the packet belongs to those connected routes.

For example, in 

 Fast Ethernet interface 0/0 is configured with two secondary addresses, 

1.1.1.1/24 and 2.1.1.1/24. The first address, 1.1.1.1/24, is assigned to VRF red, while the other, 
2.1.1.1/24, is assigned to VRF green. So in the VRF red table, a connected route 1.1.1.0/24 is installed, 
while in VRF green, 2.1.1.0/24 is installed. The routing information can be learned dynamically or 
statically defined.

There is a default route in VRF red that directs all traffic to Fast Ethernet interface 1/0, while in VRF 
green, another default route directs all traffic to Fast Ethernet interface 1/1. When packets arrive at Fast 
Ethernet interface 0/0, they are mapped to either VRF red or VRF green based on their source address. 
If the source address is 1.1.1.2, connected route 1.1.1.0/24 is used, and the packet is mapped to VRF red. 
Following the default route, it is forwarded out of Fast Ethernet interface 1/0. 

For the return traffic, packets are mapped to the VRF configured on the downstream interface. For 
example, when a packet is received by a Fast Ethernet interface, destined for host 1.1.1.2, it is marked 
VRF red automatically based on the VRF configured on the downstream interface using the ip vrf 
forwarding red command. A lookup in VRF red would return a connected route for 1.1.1.0/24 out of 
Fast Ethernet interface 0/0 or return a 1.1.1.2/32 that is a directly connected neighbor. When the 
connected route 1.1.1.0/24 is installed in vrf red while pointing out of an interface that is native to the 
global table or some other table, the table is tracked. See 

.

Fast ethernet0/0
1.1.1.1/24 vrf red
2.1.1.1/24 vrf green

VRF red
1.1.1.2

Fast ethernet1/0
ip vrf forwarding red
3.1.1.1/24

Fast ethernet1/1
ip vrf forwarding green
4.1.1.1/24

VRF red

VRF green

127902

VRF green
2.1.1.2