Hub And Spoke With Turnaround: Example - Cisco XR12000 Series Configuration Manual

Configuring Multicast Hub and Spoke Topology: Example

Hub and Spoke with Turnaround: Example

Multicast turnaround mandates a 2-interface connection to the hub site
To configure a CE as a turnaround router, it is connected to its respective PE through two interfaces and each
interface is placed in a separate hub site vrf called hub-x-in vrf and hub-x-out vrf. Hub-x-in vrf carries joins
that come from the receiver spoke site through the Hub Tunnel and hub-x-out vrf will carry the same joins
towards the source spoke site through the Spoke Tunnel without violating the four basic rules below. The
source spoke sends traffic to the spoke tunnel to hub-x-out which is turned around to the hub-tunnel on the
hub-x-in interface.
1 Hub sites sends traffic only to MDTHub.
2 Spoke sites sends traffic only to MDTspoke.
3 Hub sites receives traffic from both tunnels.
4 Spoke sites receives traffic only from MDTHub.
A2-Spoke-1 A2-Hub-2
A2-Spoke-2 A2-Hub-3in
A2-Hub-2out
A2-Spoke-3 (spoke has auto-rp)
Figure 13: Example for CE1PE1PE2 CE2Multicast Hub and Spoke Topology with Turnaround
CE1------------------ PE1 ------------------------------------------------ PE2 ------------------ CE2
Routes exported by hub sites are imported by hub sites and spoke sites. Routes exported by spoke sites are
imported by both hub-x-out and hub-x-in and hub site exports spoke routes back into the core by hub VRF
route targets. This causes routes originated from one spoke site to be learned by all other spoke sites but with
the nexthop of hub-x-out. For example, Spoke2 will see the RPF for Spoke1 reachable with nexthop of
A2-Hub-3in. This is the fundamental difference in leaking of routes which helps in achieving turnaround of
multicast traffic.
PE1:
vrf A2-Spoke-1
address-family ipv4 unicast
import route-target
4000:1
4000:2
4000:3
4000:4
!
export route-target
4001:1
!
Cisco IOS XR Multicast Configuration Guide for the Cisco XR12000 Series Router, Release 5.1.x
144
Implementing Multicast Routing on Cisco IOS XR Software
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