Multicast Distribution Tree (MDT) Notes
Multicast Distribution Tree (MDT)
– a.k.a
-> Multicast VPN (MVPN)
-> Multicast VRF (MVRF)
– Allows clients to exchange multicast traffic over MPLS L3VPN
Configuration
1. Configure multicast in the ISP
2. Configure VRF multicast on PE routers
3. Configure multicast in the customer networks
4. MDT address will be configured on all PE routers
5. MDT address will be used to form an MDT tunnel between PE routers
6. Any multicast traffic ( control plane / data plane ) coming from the customer will be encapsulated in MDT packets and sent to other PE routers
7. The receiving PE routers deencapsulate the MDT packets if the internal multicast packet is destined for local VRF
IOS Router
R1(config)# ip multicast-routing
ip multicast-routing vrf ABC
int s0/0
ip pim sparse-mode
int s0/1
ip pim sparse-mode
ip pim rp-address 2.2.2.2
ip pim vrf ABC rp-address 4.4.4.4
ip vrf ABC
mdt default 239.1.1.1
R4, R5, R6
– Basic multicast configuration
XR Router
R3(config)# multicast-routing
address-family ipv4
int s0/0
enable
vrf ABC
address-family ipv4
mdt default ipv4 239.1.1.1
int s0/1
enable
int s0/2
enable
router pim
address-family ipv4
rp-address 2.2.2.2
int s0/0
enable
vrf ABC
address-family 4.4.4.4
int s0/1
enable
int s0/2
enable
Inter-AS Option A | B | C
MDT Tunnel
– PE Address
-> Not exchanged by default
-> Solution is to send this information in BGP by using a special address-family called “mdt”
– MDT Group
-> Not exchanged by default
-> Solution is to send this information in BGP by using a special address-family called “mdt”
– ASBR routers add additional information to MDT updates called “Proxy RPF Vector”
– Proxy RPF Vector contains the intermediate next-hop for RPF checks and join message propogation
– MSDP will be required once the PE address and MDT group of the other AS is known
-> For this, the RP address for both ASs must be reachable from both ends
Configuration
1. Configure MPLS L3VPN between ASs
2. Activate multicast in both ASs separately
3. Activate MDT on PE routers
4. Configure BGP MDT address-family on PE and ASBR routers
5. Configure MSDP between RPs
6. Activate multicast on customer network
IOS Router
R1(config)# ip multicast-routing
ip multicast-routing vrf ABC
int s0/0
ip pim sparse-mode
int s0/1
ip pim sparse-mode
ip pim rp-address 2.2.2.2
ip pim vrf ABC rp-address 5.5.5.5
router bgp 100
no bgp default ipv4-unicast
neighbor 2.2.2.2 remotes-as 100
neighbor 2.2.2.2 update-source lo0
address-family ipv4 mdt
neighbor 2.2.2.2 activate
ip vrf ABC
mdt default 239.1.1.1
XR Router
R2(config)# router bgp 100
address-family ipv4 mdt
neighbor 1.1.1.1
address-family ipv4 mdt
next-hop-self
remote-as 100
update-source lo0
neighbor 23.0.0.2
address-family ipv4 mdt
IOS Router
sh bgp ipv4 mdt all
sh ip pim mdt
sh ip pim mdt bgp
sh ip pim rp mapping
sh ip pim vrf ABC rp mapping
sh ip mspd summary
sh ip mroute
sh ip mroute vrf ABC
XR Router
sh bgp ipv4 mdt
sh pim mdt
sh pim range-list
sh msdp summary
sh pim vrf ABC rp mapping
sh route ipv4 multicast
sh route vrf ABC ipv4 multicast
sh mfib route
sh mfib vrf ABC route
sh mfib mdt statistics
sh mfib vrf ABC mdt statistics
MDT Tunnel Source Address
– When MDT is configured between PE routers, they create an MDT tunnel
-> The source address of the tunnel is the LDP router-id; or if BGP is configured, then the source address of the tunnel is the highest update-source
-> To configure the tunnel source manually
IOS Router
ip vrf ABC
mdt defautl 239.1.1.1
bgp next-hop lo0
XR Router
multicast-routing
address-family ipv4
mdt source lo0
MDT Data Groups
– MDT default group is joined by all PE routers, so the traffic always goes to all PE routers
– If multicast traffic crosses a pre-specified threshold, another tunnel can be created and joined only by interested PE routers
-> This is called an MDT data group
Tunnel 239.1.1.1 -> Joined by PE 2, 3, 4, 5
TUnnel 238.1.1.1 -> Joined by PE 2, 3
Scenario -> MDT Default Group – 239.1.1.1; MDT Data Group – 238.1.1.0 – 3
IOS Routers
– On all PE routers
ip vrf ABC
mdt default 239.1.1.1
mdt data 238.1.1.0 0.0.0.3 threshold 500
XR Routers
– On all PE routers
vrf ABC
address-family ipv4
mdt default ipv4 239.1.1.1
mdt data ipv4 238.1.1.0 0.0.0.3 threshold 500
