Configuring Multicast Listener Discovery (MLD)


In IPv4, Layer 2 switches can use IGMP snooping to limit the flooding of multicast traffic by dynamically configuring Layer 2 interfaces so that multicast traffic is forwarded to only those interfaces associated with IP multicast address. In IPv6, MLD snooping performs a similar function. With MLD snooping, IPv6 multicast data is selectively forwarded to a list of ports that want to receive the data, instead of being flooded to all ports in a VLAN. This list is constructed by snooping IPv6 multicast control packets.


MLD is a protocol used by IPv6 multicast routers to discover the presence of multicast listeners (nodes configured to receive IPv6 multicast packets) on its directly attached links and to discover which multicast packets are of interest to neighboring nodes. MLD is derived from the IGMP protocol. MLD version 1 (MLDv1) is equivalent to IGMPv2, and MLD version 2 (MLDv2) is equivalent to IGMPv3. MLD is a sub-protocol of Internet Control Message Protocol version 6 (ICMPv6), and MLD messages are a subset of ICMPv6 messages, identified in IPv6 packets by a preceding Next Header value of 58.


The switch can snoop on both MLDv1 and MLDv2 protocol packets and bridge IPv6 multicast data based on destination IPv6 multicast MAC addresses. The switch can be configured to perform MLD snooping and IGMP snooping simultaneously.


To display MLD routers on the network, use the mld-router-show command:


CLI (network-admin@switch) > mld-router-show


group-ip:                

node-ip:                 

vlan:                    

port:                    

source:                  

node-type:               

expires:                 


The show output displays the following information:


  • Multicast group IP address in IPv6 format
  • Host node IP address in IPv6 format
  • Host VLAN ID
  • Port number
  • Multicast traffic source IP address in IPv6 format
  • Node type as host or router
  • Expires as the age-out time


To display MLD group membership on the network, use the mld-show command:


CLI (network-admin@switch) > mld-show


group-ip:                

node-ip:                 

vlan:                    

port:                    

source:                  

node-type:               

expires:                 


The show output displays the following information:


  • Multicast group IP address in IPv6 format
  • Host node IP address in IPv6 format
  • Host VLAN ID
  • Port number
  • Multicast traffic source IP address in IPv6 format
  • Node type as host or router
  • Expires as the age-out time


To enable or disable MLD snooping or modify the scope, use the mld-snooping-modify command:


CLI (network-admin@switch) > mld-snooping-modify


To modify the scope from fabric to local, use the following syntax:


CLI (network-admin@switch) > mld-snooping-modify scope fabric


To display information about MLD snooping, use the mld-snooping-show command.