Comware Multicast Routing with PIM-SM and IGMP

IGMP snooping

IGMP snooping runs on a Layer 2 switch as a multicast constraining mechanism to improve multicast forwarding efficiency. It creates Layer 2 multicast forwarding entries from IGMP packets that are exchanged between the hosts and the router.  When IGMP snooping is not enabled, the Layer 2 switch floods multicast packets to all devices. When IGMP snooping is enabled, the Layer 2 switch forwards multicast packets of known multicast groups to only the receivers.

Common notations in multicast

The following notations are commonly used in multicast transmission:

o    (*, G)—Rendezvous point tree (RPT), or a multicast packet that any multicast source sends to multicast group G. The asterisk (*) represents any multicast source, and "G" represents a specific multicast group.

o    (S, G)—Shortest path tree (SPT), or a multicast packet that multicast source "S" sends to multicast group "G." "S" represents a specific multicast source, and "G" represents a specific multicast group.

Multicast Routing

IGMP (delivers the multicast to the host)

PIM (delivers the multicast to the switch)

IGMP

show commands

display igmp group

display igmp-snooping group

Minimize multicast flooding

igmp-snooping

Enable in vlan

vlan X

 igmp-snooping enable

IGMP & MSTP

Set static router ports to recover from failed links more quickly.

Timers

igmp robust-count x

     

x = times the query interval plus the max response time - default 2

igmp max-response-time 10 (default)

igmp last-member-query-interval 1 (default)

IGMP Example

vlan 12

 description Jumbo Frame Multicast VLAN

 igmp-snooping enable

 igmp-snooping drop-unknown ß This is highly recommended if using jumbo frames

 igmp-snooping querier ß Makes a querier for the vlan segment

Multicast Routing

·         Enable globally

multicast routing

PIM

display multicast routing-table

display pim routing-table

PIM-SM

·         Does not forward multicasts unless requested to by a join message

·         Periodic joins required to maintain the tree

·         Used on lower bandwidth router connections

Configuring PIM-SM

Enable PIM-SM on every interface between multicast sources and receivers, including:

·         Interfaces on which multicast sources reside

·         Interfaces on which multicast receivers reside (IGMP-enabled interfaces)

·         Interfaces between all routers and routing switches that connect sources and receivers

(*, G) entry has an upstream interface, which enables the PIM routing switch to explicitly join the tree. The switch discovers the upstream interface by looking up the forwarding interface in the unicast route to the RP.

interface vlan 10

 igmp enable

 igmp version 3

 pim sm

·         Every PIM-SM router or routing switch in the domain must always select the same RP for the same multicast addresses.

·         Should be backbone routers.

·         Near the multicast source.

Dynamic RP:

·         For the simplest setup, have all C-RPs advertise support for all multicast addresses with the same priority.  Set the priority on all C-RPs to the same value:

pim

 c-rp <interface type> <number> priority <0-255> ß Comware 5

 c-rp <ip address> priority <0-255> ß Comware 7

·         It is best to explicitly set the same priority on each C-RP because different models of switches could use different default priorities.

·         This allows the hash function to select RPs.

·         Adjust the hash mask length on C-BSRs to adjust the size of the block of addresses always assigned to the same RP

-          Default: 30 (block of four)

CM5

pim

 c-bsr <interface type> <number> <0-32>

-or-

 c-bsr <interface type> <number>

 c-bsr hash-length <0-32>

CM7

pim

 c-bsr <ip address> <0-32>

-or-

 c-bsr <ip address>

 c-bsr hash-length <0-32>

Bootstrap and RP Routers

multicast routing-enable

igmp

interface vlan 10

 igmp enable

 igmp version 3

 pim sm

pim

 c-bsr hash-length 24

 c-bsr priority 100

 c-bsr Vlan-interface10 priority 100

 --or—

 c-bsr 10.1.1.1 priority 100

Other Routers

multicast routing-enable

igmp

interface vlan 10

 ip address 10.x.x.x 255.255.255.0

 igmp enable

 igmp version 3

 pim sm

Layer 2 Switches (Non-Querier)

igmp-snooping

vlan X

 igmp-snooping enable