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Configuring Hub-and-Spoke VPN Topologies: One Interface
Use a one-interface configuration to advertise
a default route from a hub or hubs.
Figure 22: Example of a Hub-and-Spoke VPN Topology
with One Interface
Figure 22 illustrates a
Layer 3 VPN hub-and-spoke application where there is only one interface
between the hub CE (CE1) and the hub PE (PE1). This is the recommended
way of configuring hub-and-spoke topologies.
In this configuration, a default route is advertised
from the hub to the spokes. If more specific spoke CE routes need
to be exchanged between spoke CE routers, then two interfaces are
needed between the hub CE and hub PE. See Configuring Hub-and-Spoke VPN Topologies: Two Interfaces for a two-interface example.
In this configuration example, spoke route distribution
is as follows:
- Spoke CE2 advertises its routes to spoke PE2.
- Spoke PE2 installs routes from CE2 into its VPN routing
and forwarding (VRF) table.
- Spoke PE2 checks its VRF export policy, adds the route
target community, and announces the routes to hub PE1.
- Hub PE1 checks its VRF import policy and installs routes
that match the import policy into table bgp.l3vpn.0.
- Hub PE1 installs routes from table bgp.l3vpn.0 into the hub VRF table.
- Hub PE1 announces routes from the hub VRF table to the
hub CE1.
In this configuration example, default route distribution
is as follows:
- Hub CE1 announces a default route to hub PE1.
- Hub PE1 installs the default route into the hub VRF table.
- Hub PE1 checks its VRF export policy, adds the route target
community and announces the default route to spoke PE2 and PE3.
- Spoke PE2 and PE3 check their VRF import policy and install
the default route into table bgp.l3vpn.0.
- Spoke PE2 and PE3 install the routes from table bgp.l3vpn.0 into their spoke VRF tables.
- Spoke PE2 and PE3 announce the default route from the
spoke VRF table to spoke CE2 and CE3.
The following sections describe how to configure
a hub-and-spoke topology with one interface based on the topology
illustrated in Figure 22:
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