Multicast
Multicast is a “one source, many destinations” method of traffic distribution, meaning only the destinations that explicitly indicate their need to receive the information from a particular source receive the traffic stream.
Network applications that can function with unicast but are better suited for multicast include collaborative groupware, teleconferencing, periodic or “push” data delivery (stock quotes, sports scores, magazines, newspapers, and advertisements), server or website replication, and distributed interactive simulation (DIS) such as war simulations or virtual reality. Any IP network concerned with reducing network resource overhead for one-to-many or many-to-many data or multimedia applications with multiple receivers benefits from multicast.
Please refer to the Juniper Multicast Overview for more in-depth information about Multicast.
Version History
| Release | Modification |
|---|---|
| 6.1.0 | This feature was introduced |
| 6.2.0 | Added support for MSDP, SSR as RP |
Multicast on the SSR
Multicast on the SSR supports the following protocols and topology:
- PIM Sparse-Mode
- PIM Source-Specific Multicast (PIM-SSM)
- Static Configuration of RP
- IGMP v2/v3
- Multicast over SVR in Hub and Spoke topology
Multicast Configuration
In order to support Multicast over SVR, the BGP over SVR configuration is used in conjunction with the PIM configuration to generate auto-provisioned services and service-paths. BGP over SVR must be provisioned to support the Multicast feature. See BGP over SVR for configuration details.
The following are the components necessary to configure multicast over SVR on the SSR. Configuration for each of the components is provided below, and a full example configuration is provided at the end of this process.
- Routing Interface: Specify the BGP over SVR interface
- BGP over SVR: See BGP over SVR for configuration details.
- Routing protocol such as IGMPv2/v3
- PIM
- RP: The Rendezvous Point. In the initial implementation (v6.1.x), the RP must be external to the SSR. This has been revised and the configuration below offers both configurations.
- Service: Services are created for the multicast traffic, and defined for the Group address.
- Multicast-sender-policy: Defines the tenant that is allowed to be the source of the multicast stream.
- Access Policy: Configures the tenants allowed to receive the multicast traffic via IGMP joins at routers in the network.
Refer to Tenants for more information on configuring Tenants.
Multicast Source Discovery Protocol (MSDP) is a protocol that allows inter-domain multicast communication. MSDP is only valid for the Any-Source Multicast (ASM) model. If the Source-Specific Multicast (SSM) model is used, MSDP will not send Source-Active (SA) messages to indicate an active source.
Configuration Process
The following diagram represents a simple multicast configuration. A Client sends a multicast to address 225.1.1.1. Location1 and Location2 want to receive this multicast stream. The network is setup to use an external, non-SSR Rendezvous Point (RP) at 20.20.20.20 for all multicast traffic. This router is 192.168.22.2 and is configured for BGP with SSR rtr2. It advertises 20.20.20.20 as the RP for multicast into BGP, allowing the SSR network to identify the path to the RP.
Key points in the rtr2 configuration:
- BGP is configured with the external router, 192.168.22.2
- BGP over SVR is configured with two spokes
- PIM is configured on the LAN interface towards the external router
- The tenant
edselis configured on the LAN interface
Configuration for rtr2
config
authority
router rtr2
node node1
name node1
device-interface eth6
network-interface lan3
name lan3
tenant edsel
address 192.168.22.1
ip-address 192.168.22.1
prefix-length 30
gateway 192.168.22.2
exit
exit
exit
exit
routing default-instance
type default-instance
routing-protocol bgp
type bgp
local-as 65128
neighbor 192.168.22.2
neighbor-address 192.168.22.2
neighbor-as 65100
exit
neighbor 192.168.128.0
neighbor-address 192.168.128.0
neighbor-as 65128
transport
local-address
routing-interface loopback0
exit
exit
address-family ipv4-unicast
afi-safi ipv4-unicast
next-hop-self true
exit
exit
neighbor 192.168.128.1
neighbor-address 192.168.128.1
neighbor-as 65128
transport
local-address
routing-interface loopback0
exit
exit
address-family ipv4-unicast
afi-safi ipv4-unicast
next-hop-self true
exit
exit
exit
pim
interface node1 lan3
node node1
interface lan3
exit
rp 224.0.0.0/4
address 20.20.20.20
group-range 224.0.0.0/4
exit
exit
To use rtr2 as the Rendezvous Point, the existing static RP configuration takes the IP address of the RP. This address should be a routable address configured on rtr2. The SSR detects this address as one of its local interfaces and assumes the role of RP. It is recommended to create a routing-interface (unrelated to BGPoSVR configuration) to be a routable address of the local RP. This routing interface must be advertised in the routing protocol. To do this either enable OSPF on the interface, or advertise the address using a BGP network command. For example:
Create the Routing Interface:
routing default-instance
type default-instance
interface loopback-rp
name loopback-rp
ip-address 192.168.128.0
exit
Advertise the Address using BGP:
routing-protocol bgp
type bgp
address-family ipv4-unicast
afi-safi ipv4-unicast
network 192.168.128.0/32
network-address 192.168.128.0/32
exit
exit
Configuration for Spoke 1 (rtr0)
Key points for the Spoke configuration - this applies to each spoke, since the configuration is nearly identical.
- BGP over SVR configured to the hub
- PIM configured with the same RP on the LAN interface
- IGMP configured on the LAN interface
- Using tenant
studebakeron the LAN where the IGMP joins originate
config
authority
router rtr0
node node1
device-interface eth3
network-interface lan0
tenant studebaker
address 192.168.0.1
ip-address 192.168.0.1
prefix-length 24
exit
exit
exit
exit
routing default-instance
type default-instance
interface loopback0
name loopback0
ip-address 192.168.128.0
exit
routing-protocol bgp
type bgp
local-as 65128
address-family ipv4-unicast
afi-safi ipv4-unicast
network 192.168.0.0/24
network-address 192.168.0.0/24
exit
exit
neighbor 192.168.128.2
neighbor-address 192.168.128.2
neighbor-as 65128
transport
local-address
routing-interface loopback0
exit
exit
exit
exit
igmp
interface node1 lan0
node node1
interface lan0
exit
exit
pim
interface node1 lan0
node node1
interface lan0
exit
rp 225.0.0.0/4
address 20.20.20.20
group-range 225.0.0.0/4
exit
exit
exit
exit
exit
exit
Configuration for Spoke 2 (rtr1)
config
authority
router rtr1
node node1
device-interface eth3
network-interface lan0
tenant studebaker
address 192.168.1.1
ip-address 192.168.1.1
prefix-length 24
exit
exit
exit
exit
routing default-instance
type default-instance
interface loopback0
name loopback0
ip-address 192.168.128.1
exit
routing-protocol bgp
type bgp
local-as 65128
address-family ipv4-unicast
afi-safi ipv4-unicast
network 192.168.1.0/24
network-address 192.168.1.0/24
exit
exit
neighbor 192.168.128.2
neighbor-address 192.168.128.2
neighbor-as 65128
transport
local-address
routing-interface loopback0
exit
exit
exit
exit
igmp
interface node1 lan0
node node1
interface lan0
exit
exit
pim
interface node1 lan0
node node1
interface lan0
exit
rp 224.0.0.0/4
address 20.20.20.20
group-range 224.0.0.0/4
exit
exit
exit
exit
exit
exit
Configure the Service
The service allows the traffic to flow. It allows the tenant from the hub edsel to send the multicast stream, and the tenants studebaker on each spoke can join and receive the multicast stream.
config
authority
service multicast
name multicast
address 224.0.0.0/4
access-policy studebaker
source studebaker
exit
multicast-sender-policy edsel
source edsel
exit
exit
exit
exit
Other Considerations
While this configuration example uses one RP for the multicast range, you can use different RPs for different multicast addresses or ranges. The same can be done for the service; smaller services for more specific ranges of multicast with different senders and receivers as needed.
Multicast Source Discovery Protocol (MSDP)
MSDP is used to allow RPs to share the active Multicast Sources. Messages are sent as Source-Active (SA) messages between MSDP peers. In normal MSDP operation, an MSDP peer is received from one peer and forwarded to the other MSDP peers. To ensure there are no loops, RPF checks have been put in place.
MSDP can also be configured as a mesh-group. In this mode, the SA messages received from a peer are not forwarded to the other members of the mesh-group, since all the peers are configured as part of the mesh. This is commonly used with Anycast RPs, where the same RP address is configured on multiple routers in the network. The Anycast RP routers use an MSDP mesh-group to distribute the active source information to the other anycast RPs. This provides redundancy in the network, in case an RP fails.
Configuration
MSDP can be configured on the router as follows:
authority
router A
routing default-instance
msdp
peer 10.10.10.2 source 16.0.0.2
exit
exit
Alternatively, MSDP can be configured with a mesh-group. A mesh-group is similar to an IBGP peering relationship, in that the received SA messages are not forwarded to other members of the mesh-group.
authority
router A
routing default-instance
msdp
peer 10.10.10.2 source 16.0.0.2
mesh-group myMesh
source 16.0.0.2
member 11.11.11.1
exit
exit
exit
MSDP can also be enabled in a VRF:
authority
router A
routing default-instance
vrf vrfA
msdp
peer 10.10.10.2 source 16.0.0.2
exit
exit
exit
Show Commands
Each of the commands listed below and the subcommands for each, provide additional details for multicast visibility. Use the links to learn more about each command.
| Command | Description |
|---|---|
| show igmp interface | Display the igmp interfaces |
| show igmp groups | Display the igmp groups |
| show msdp peer | Display MSDP peer information |
| show msdp mesh-group | Display MSDP mesh-group details |
| show msdp sa | Display MSDP source active |
| show pim mroute | Display the PIM mroute |
| show pim interface | Display the PIM interface |
| show pim join | Display the PIM Joins |
| show pim neighbor | Display the PIM neighbor |
| show pim rp-info | Display the PIM RP info |
| show pim state | Display the PIM state |
Each show command allows a vrf option:
show ip igmp [vrf <vrfname>]