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Software Configuration Guide—Release 12.2(25)SG
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Chapter26 Configuring VRF-lite
Understanding VRF-lite
Understanding VRF-lite
VRF-lite is a feature that enables a service provider to support two or more VPNs, where IP addresses
can be overlapped among the VPNs. VRF-lite uses input inte rfaces to distinguish routes for different
VPNs and forms virtual packet-forwarding tables by associating one or more Layer 3 interfaces with
each VRF. Interfaces in a VRF can be either physical, such as Ethernet ports, or logical, such as VLAN
SVIs, but a Layer 3 interface cannot belong to more than one VRF at any time.
Note VRF-lite interfaces must be Layer 3 interfaces.
VRF-lite includes these devices:
•Customer edge (CE) devices provide customer access to the service provider network over a data
link to one or more provider edge routers. The CE device advertises the site’s local routes to the
provider edge router and learns the remote VPN routes from it. A Catalyst 4500 switch can be a CE.
•Provider edge (PE) routers exchange routing information with CE devices by using static routing or
a routing protocol such as BGP, RIPv1, or RIPv2.
•The PE is only required to maintain VPN routes for those VPNs to which it is directly attached,
eliminating the need for the PE to maintain all of the service provider VPN routes. Each PE router
maintains a VRF for each of its directly connected sites. Multiple interfaces on a PE router can be
associated with a single VRF if all of these sites participate in the same VPN. Each VPN is mapped
to a specified VRF. After learning local VPN routes from CEs, a PE router exchanges VPN routing
information with other PE routers by using internal BGP (IBPG).
•Provider routers (or core routers) are any routers in the service provider network that do not attach
to CE devices.
With VRF-lite, multiple customers can share one CE, and only one physical link is used between the CE
and the PE. The shared CE maintains se parate VRF tables for each customer and sw itches or routes
packets for each customer based on its own routing table. VRF-lite extends limited PE functionality to
a CE device, giving it the ability to maintain separate VRF tables to extend the privacy and security of
a VPN to the branch office.
Figure 26-1 shows a configuration where each Catalyst 4500 switch acts as multiple virtual CEs.
Because VRF-lite is a Layer 3 feature, each interface in a VRF must be a Layer 3 interface.
Figure26-1 Catalyst 4500 Switches Acting as Multiple Virtual CEs
VPN 1
VPN 2
VPN 1
VPN 2
CE
MPLS-VRF
router
MPLS-VRF
router
Catalyst 4500
switch
Catalyst 4500
switch
PE PE
MPLS
network
CE
CE = Customer edge device
PE = Provider edge router
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