The partitioned-MDT picks up the traffic from the partitioned-tree to forward to the RP. No DF election is
needed on the MDT in this scheme. Routers that do not understand the new BIDIR AD route do not join the
BIDIR partitioned-MDT.
There are no interoperability issues even if there are PE routers in the network that do not support BIDIR.Note
Multicast VPN Hub and Spoke Topology
Hub and spoke topology is an interconnection of two categories of sites — Hub sites and Spoke sites. The
routes advertised across sites are such that they achieve connectivity in a restricted hub and spoke fashion. A
spoke can interact only with its hub because the rest of the network (that is, other hubs and spokes) appears
hidden behind the hub.
The hub and spoke topology can be adopted for these reasons:
•
Spoke sites of a VPN customer receives all their traffic from a central (or Hub) site hosting services
such as server farms.
•
Spoke sites of a VPN customer requires all the connectivity between its spoke sites through a central
site. This means that the hub site becomes a transit point for interspoke connectivity.
•
Spoke sites of a VPN customer do not need any connectivity between spoke sites. Hubs can send and
receive traffic from all sites but spoke sites can send or receive traffic only to or from Hub sites.
Both Cisco CRS and Cisco XR 12000 Series routers support MVPN v4 Hub-and-spoke implementation.
But MVPNv6 Hub-and-spoke is not supported on Cisco CRS Router.
Note
Realizing the Hub and Spoke Topology
Hub and Spoke implementation leverages the infrastructure built for MVPN Extranet. The regular MVPN
follows the model in which packets can flow from any site to the other sites. But Hub and Spoke MVPN will
restrict traffic flows based on their subscription.
A site can be considered to be a geographic location with a group of CE routers and other devices, such as
server farms, connected to PE routers by PE-CE links for VPN access. Either every site can be placed in a
separate VRF, or multiple sites can be combined in one VRF on the PE router.
By provisioning every site in a separate VRF, you can simplify the unicast and multicast Hub and Spoke
implementation. Such a configuration brings natural protection from traffic leakage - from one spoke site to
another. Cisco IOS XR Software implementation of hub and spoke follows the one- site-to-one VRF model.
Any site can be designated as either a hub or spoke site, based on how the import or export of routes is setup.
Multiple hub and spoke sites can be collated on a given PE router.
Unicast Hub and Spoke connectivity is achieved by the spoke sites importing routes from only Hub sites, and
Hub sites importing routes from all sites. As the spoke sites do not exchange routes, spoke to spoke site traffic
cannot flow. If interspoke connectivity is required, hubs can choose to re-inject routes learned from one spoke
site into other spoke site.
Cisco IOS XR Multicast Configuration Guide for the Cisco CRS Router, Release 5.2.x
27
Implementing Multicast Routing on Cisco IOS XR Software
Multicast VPN Hub and Spoke Topology
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