Configuring MLD Snooping

Function Introduction

Layer 2 switches can use MLD snooping to constrain the flooding of multicast traffic by dynamically configuring Layer 2 interfaces so that multicast traffic is forwarded only to those interfaces associated with IPv6 multicast devices. As the name implies, MLD snooping requires the LAN switch to snoop on the MLD transmissions between the host and the router and to keep track of multicast groups and member ports. When the switch receives an MLD report from a host for a particular multicast group, the switch adds the host port number to the forwarding table entry; when it receives an MLD Leave Group message from a host, it removes the host port from the table entry. It also deletes entries per entry if it does not receive MLD membership reports from the multicast clients. The multicast router sends out periodic general queries to all VLANs. All hosts interested in this multicast traffic send report and are added to the forwarding table entry. The switch forwards only one report per IPv6 multicast group to the multicast router. It creates one entry per VLAN in the Layer 2 forwarding table for each MAC group from which it receives an MLD report.

Layer 2 multicast groups learned through MLD snooping are dynamic. If you specify group membership for a multicast group address statically, your setting supersedes any automatic manipulation by MLD snooping. Multicast group membership lists can consist of both user-defined and MLD snooping-learned settings.

Limitations And Configuration Guideline

VRRP, RIPng and OSPFv3 used multicast IPv6 address, so you need to avoid use such multicast IPv6 addresses, which have same multicast MAC address with multicast IPv6 address reserved by VRRP, RIPng and OSPFv3.

• VRRP used multicast group address ff02::12, so when mld snooping and VRRP are working, you need to avoid using multicast group address that matched same mac address with group address ff02::12.

• OSPFv3 used multicast group address ff02::5, so when mld snooping and OSFPv3 are working, you need to avoid using multicast group address that matched same mac address with group address ff02::5.

• RIPng used multicast group address ff02::9, so when mld snooping and RIPng are working, you need to avoid using multicast group address that matched same mac address with group address ff02::9.

Principle Description

N/A

Enable MLD Snooping

Switch# show ipv6 mld snooping vlan 1
Global Mld Snooping Configuration

Mld Snooping :Enabled
Mld Snooping Fast-Leave :Disabled
Mld Snooping Version :1
Mld Snooping Max-Member-Number :4096
Mld Snooping Unknown Multicast Behavior :Flood
Mld Snooping Report-Suppression :Enabled
Vlan 1

Mld Snooping :Enabled
Mld Snooping Fast-Leave :Disabled
Mld Snooping Report-Suppression :Enabled
Mld Snooping Version :1
Mld Snooping Max-Member-Number :4096
Mld Snooping Unknown Multicast Behavior :Flood
Mld Snooping Group Access-list :N/A
Mld Snooping Mrouter Port :
Mld Snooping Mrouter Port Aging Interval(sec) :255

Configuring Fast Leave

When MLD Snooping fast leave is enabled, the mld snooping group will be removed at once upon receiving a corresponding mld report. Otherwise the switch will send out specified mld specific query, if it doesn’t get response in specified period, it will remove the group. By default, mld snooping fast-leave is disabled globally and per vlan.

Switch# show ipv6 mld snooping vlan 1
Global Mld Snooping Configuration

Mld Snooping :Enabled
Mld Snooping Fast-Leave :Enabled
Mld Snooping Version :1
Mld Snooping Max-Member-Number :4096
Mld Snooping Unknown Multicast Behavior :Flood
Mld Snooping Report-Suppression :Enabled
Vlan 1

Mld Snooping :Enabled
Mld Snooping Fast-Leave :Enabled
Mld Snooping Report-Suppression :Enabled
Mld Snooping Version :1
Mld Snooping Max-Member-Number :4096
Mld Snooping Unknown Multicast Behavior :Flood
Mld Snooping Group Access-list :N/A
Mld Snooping Mrouter Port :
Mld Snooping Mrouter Port Aging Interval(sec) :255

Configuring Querier Parameters (optional)

In order for MLD, and thus MLD snooping, to function, a multicast router must exist on the network and generate MLD queries. The tables created for snooping (holding the member ports for each multicast group) are associated with the querier. Without a querier the tables are not created and snooping will not work.

Switch(config)# ipv6 mld snooping query-interval 100
Switch(config)# ipv6 mld snooping query-max-response-time 5

Switch(config)# ipv6 mld snooping vlan 1 querier address fe80::1
Switch(config)# ipv6 mld snooping vlan 1 querier
Switch(config)# ipv6 mld snooping vlan 1 query-interval 200
Switch(config)# ipv6 mld snooping vlan 1 query-max-response-time 5
Switch(config)# ipv6 mld snooping vlan 1 querier-timeout 100
Switch(config)# ipv6 mld snooping vlan 1 last-member-query-interval

Switch(config)# ipv6 mld snooping vlan 1 discard-unknown

Switch# show ipv6 mld snooping querier
Global Mld Snooping Querier Configuration

Version :1
Last-Member-Query-Interval (msec) :2000
Max-Query-Response-Time (sec) :5
Query-Interval (sec) :100
Global Source-Address :::
TCN Query Count :2
TCN Query Interval (sec) :10
Vlan 1: MLD snooping querier status

Elected querier is : fe80::1

Admin state :Enabled
Admin version :1
Operational state :Querier
Querier operational address :fe80::1
Querier configure address :fe80::1
Last-Member-Query-Interval (msec) :2000
Max-Query-Response-Time (sec) :5
Query-Interval (sec) :200
Querier-Timeout (sec) :100

Configuring Mrouter Port

An MLD Snooping mrouter port is a switch port which is assumed to connect a multicast router. The mrouter port is configured on the vlan or learnt dynamicly. When MLD general query packet or PIMv6 hello packet is received on port of specified VLAN, this port becomes mrouter port of this vlan. All the mld queries received on this port will be flooded on the belonged vlan. All the mld reports and leaves received on this vlan will be forwarded to the mrouter port, directly or aggregated, depending on the report-suppression configuration. In addition, all the multicast traffic on this vlan will be forwarded to this mrouter port.

Switch(config)# ipv6 mld snooping vlan 1 report-suppression
Switch(config)# ipv6 mld snooping vlan 1 mrouter-aging-interval 200

Switch# show ipv6 mld snooping vlan 1
Global Mld Snooping Configuration

Mld Snooping :Enabled
Mld Snooping Fast-Leave :Enabled
Mld Snooping Version :1
Mld Snooping Max-Member-Number :4096
Mld Snooping Unknown Multicast Behavior :Discard
Mld Snooping Report-Suppression :Enabled
Vlan 1

Mld Snooping :Enabled
Mld Snooping Fast-Leave :Enabled
Mld Snooping Report-Suppression :Enabled
Mld Snooping Version :1
Mld Snooping Max-Member-Number :4096
Mld Snooping Unknown Multicast Behavior :Discard
Mld Snooping Group Access-list :N/A
Mld Snooping Mrouter Port :eth-0-1(static)
Mld Snooping Mrouter Port Aging Interval(sec) :200

Configuring Querier Tcn

User can set the TCN interval and query count to adapt the multicast learning and updating after STP converging.

Switch(config)# ipv6 mld snooping querier tcn query-count 5
Switch(config)# ipv6 mld snooping querier tcn query-interval 20

Switch# show ipv6 mld snooping querier
Global Mld Snooping Querier Configuration

Version :1
Last-Member-Query-Interval (msec) :2000
Max-Query-Response-Time (sec) :5
Query-Interval (sec) :100
Global Source-Address :::
TCN Query Count :5
TCN Query Interval (sec) :20
Vlan 1: MLD snooping querier status

Elected querier is : fe80::1

Admin state :Enabled
Admin version :1
Operational state :Querier
Querier operational address :fe80::1
Querier configure address :fe80::1
Last-Member-Query-Interval (msec) :2000
Max-Query-Response-Time (sec) :5
Query-Interval (sec) :200
Querier-Timeout (sec) :100

Configuring Report Suppression

The switch uses MLD report suppression to forward only one MLD report per multicast router query to multicast devices. When MLD router suppression is enabled (the default), the switch sends the first MLD report from all hosts for a group to all the multicast routers. The Switch# does not send the remaining MLD reports for the group to the multicast routers. This feature prevents duplicate reports from being sent to the multicast devices.

Switch# show ipv6 mld snooping
Global Mld Snooping Configuration

Mld Snooping :Enabled
Mld Snooping Fast-Leave :Disabled
Mld Snooping Version :2
Mld Snooping Max-Member-Number :4096
Mld Snooping Unknown Multicast Behavior :Flood
Mld Snooping Report-Suppression :Enabled
Vlan 1

Mld Snooping :Enabled
Mld Snooping Fast-Leave :Disabled
Mld Snooping Report-Suppression :Enabled
Mld Snooping Version :2
Mld Snooping Max-Member-Number :4096
Mld Snooping Unknown Multicast Behavior :Flood
Mld Snooping Group Access-list :N/A
Mld Snooping Mrouter Port :
Mld Snooping Mrouter Port Aging Interval(sec) :255

Configuring Static group

The switch can build MLD Snooping Group when receiving MLD report packet on Layer 2 port of specified VLAN. We also support configure static MLD Snooping Group by specifying MLD group, Layer 2 port and VLAN.

Switch# show ipv6 mld snooping groups
VLAN Interface Group Address Uptime Expire-time
1 eth-0-2 ff0e::1234 00:00:02 stopped