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Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
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Chapter 38 Configuring IP Unicast Routing
Configuring Multi-VRF CE
Figure 38-6
Switches Acting as Multiple Virtual CEs
When the CE switch receives a command to add a Layer 3 interface to a VRF, it sets up the mapping
between the VLAN ID and the policy label (PL) in multi-VRF-CE-related data structures and adds the
VLAN ID and PL to the VLAN database.
When multi-VRF CE is configured, the Layer 3 forwarding table is virtually partitioned into two
sections:
•
The multi-VRF CE routing section contains the routes from different VPNs.
•
The global routing section contains routes to non-VPN networks, such as the Internet.
VLAN IDs from different VRFs are mapped to different policy labels, which are used to distinguish the
VRFs during processing. For each new VPN route learned, the Layer 3 setup function retrieves the policy
label by using the VLAN ID of the ingress port and inserts the policy label and the new route to the
multi-VRF CE routing section. If the packet is received from a routed port, the port internal VLAN ID
number is used; if the packet is received from an SVI, the VLAN number is used.
This is the packet-forwarding process in a multi-VRF-CE-enabled network:
•
When the switch receives a packet from a VPN, the switch looks up the routing table based on the
input policy label number. When a route is found, the switch forwards the packet to the PE.
•
When the ingress PE receives a packet from the CE, it performs a VRF lookup. When a route is
found, the router adds a corresponding MPLS label to the packet and sends it to the MPLS network.
•
When an egress PE receives a packet from the network, it strips the label and uses the label to
identify the correct VPN routing table. Then it performs the normal route lookup. When a route is
found, it forwards the packet to the correct adjacency.
•
When a CE receives a packet from an egress PE, it uses the input policy label to look up the correct
VPN routing table. If a route is found, the PE forwards the packet within the VPN.
To configure VRF, you create a VRF table and specify the Layer 3 interface associated with the VRF.
Then you configure the routing protocols in the VPN and between the CE and the PE. BGP is the
preferred routing protocol used to distribute VPN routing information across the provider’s backbone.
The multi-VRF CE network has these major components:
•
VPN route target communities—lists of all other members of a VPN community. You need to
configure VPN route targets for each VPN community member.
•
Multiprotocol BGP peering of VPN community PE routers—propagates VRF reachability
information to all members of a VPN community. You need to configure BGP peering in all PE
routers within a VPN community.
VPN 1
VPN 2
VPN 1
VPN 2
CE2
PE1
PE2
Service
provider
CE1
CE = Customer-edge device
PE = Provider-edge device
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