In the previous blog, we discussed IP Multicast in detail. This blog provides a guide on how to configure IP Multicast. Configuring Multicast is relatively straightforward, so this should be a short blog!

Protocol Independent Multicast (PIM) Configuration

PIM-SM (Sparse Mode) Configuration

To configure PIM on a Cisco Nexus switch, the PIM feature first needs to be enabled, both globally on the device, and also on the interface:

feature pim
interface ethernet 2/1-3
  ip pim sparse-mode

We then need to configure the Rendezvous Point (RP).

There are three ways to determine the RP:

1. Configure Static RP address Use the global command below. This command sets the RP address for the group based on the IP prefix set as group-list.

ip pim rp-address 10.10.0.1 group-list 224.0.0.1.2/9

2. Configure Auto-RP To configure Auto-RP, which is Cisco’s proprietary method of picking a Rendezvous Point, we need to configure one or more RP candidates and one or more mapping agents. The RP Candidates are devices that could be selected as RP, while the mapping agents are responsible for RP discovery and distribution.

ip pim auto-rp rp-candidate ethernet 7/21 group-list 244.0.0.2/24
ip pim auto-rp mapping-agent ethernet 5/12

3. Configure BSR BSR - Bootstrap Router is the IETF standard for RP election. The elected BSR doesn’t discover the selected RP; instead, it sends all RP candidates to routers, and the routers pick the best RP for the router itself based on a hash algorithm. You need to configure one or more BSR candidates and one or more RP candidates. To advertise a router as a BSR candidate, you need to set the interface, the hash mask length (range: 0-32; default: 30), and the BSR priority (range: 0-255; default: 64).

ip pim rp-candidate ethernet 7/21 group-list 244.0.0.2/24
ip pim bsr-candidate ethernet 9/1 hash-len 30 priority 192

BIDIR-PIM (BiDirectional Mode) Configuration

The configuration for BIDIR is practically the same as with SM, with the only difference being the addition of the “bidir” attribute. Any of the three methods could be used to set the rendezvous point:

ip pim rp-address 10.10.0.1 group-list 224.0.0.1.2/9 bidir
ip pim auto-rp rp-candidate ethernet 7/21 group-list 244.0.0.2/24 bidir
ip pim rp-candidate ethernet 7/21 group-list 244.0.0.2/24 bidir

PIM-SSM (Specific Shared Mode) Configuration

With SSM Mode, a rendezvous point is not needed as only source distribution trees are used. However, PIM-SSM requires IGMPv3 instead of the default IGMPv2 on the interface facing the receiver.

ip pim ssm range 224.0.0.1/24
int ethernet 1/2
 ip igmp version 3

PIM Anycast-RP Configuration

With the Anycast mode, multiple routers can actively serve as the RP in the same multicast group. This is possible because multiple routers can be configured with the same IP and set to be in an Anycast set. Routers in the multicast group communicate with the closest RP based on the unicast routing protocol running. A huge benefit of this mode is the advantage of load balancing requests across multiple devices.

Configuration steps to configure a PIM Anycast-RP set:

interface loopback {number}
 ip address {ip-prefix}
ip pim anycast-rp {anycast-rp-address} {anycast-rp-peer-address}

For example, to configure a loopback interface with IP address 10.1.1.1 and Anycast-RP address 192.168.1.1 with peer address 192.168.1.2:

interface loopback 0
 ip address 10.1.1.1 255.255.255.255
ip pim anycast-rp 192.168.1.1 192.168.1.2

Remember to perform similar configurations on all the routers participating in the Anycast RP set.

PIM Verification

To verify interfaces that are activated for PIM, use the command below:

show ip pim interface brief

To examine PIM neighbors, use the command below:

show ip pim neighbor

To view RP information:

show ip pim rp

To view the multicast routing table:

show ip mroute

IGMP and MLD Configuration

Specifying IGMP and MLD Versions

IGMP (Internet Group Management Protocol) and MLD (Multicast Listener Discovery) are automatically configured on interfaces in the Cisco Nexus Switch; however, both IGMP and MLD default versions are version 2. For IGMP, if SSM (Source-Specific Multicast) is needed, IGMPv3 needs to be configured. Below is an example:  

Interface ethernet1/1
  ip igmp version 3
  ip mld version 3

IGMP and MLD Verification

To verify interfaces activated for IGMP, use the command below:

show ip igmp interface brief

To verify receivers for specific groups, use the following command:

show ip igmp groups 239.1.1.1

For MLD, similar commands are used:

show ipv6 mld interface
show ipv6 mld groups

IGMP Snooping Configuration

To enable switches to be IGMP aware, IGMP snooping needs to be configured on the switch. IGMP Snooping is enabled globally by default.

IGMP Snooping can be enabled or disabled globally or per VLAN. Take a look at the commands below:  

no ip igmp snooping
vlan 45
  no ip igmp snooping
vlan 23
  ip igmp snooping

Conclusion

This concludes our concise guide to configuring IP Multicast on Cisco Nexus switches. Despite the relative simplicity of the configurations, a firm grasp of these protocols is essential for effective multicast traffic management. For those seeking more comprehensive information and advanced configuration options, consulting the official Cisco documentation is always recommended.