In order to make multicast work we need to study the following 3 areas:
1, multicast address (ip and mac)
2, IGMP protocal (to make host join or leave a multicast group)
3, IP mulicast routing protocal (PIM is mostly used)
1, Multicast address
IP multicast address 126.96.36.199 -188.8.131.52 are all multicast address, especially
184.108.40.206 The All Hosts multicast group addresses all hosts on the same network segment.
220.127.116.11 The All Routers multicast group addresses all routers on the same network segment.
18.104.22.168 This address is used in the Distance Vector Multicast Routing Protocol (DVMRP) to address multicast routers.
22.214.171.124 The Open Shortest Path First (OSPF) All OSPF Routers address is used to send Hello packets to all OSPF routers on a network segment.
126.96.36.199 The OSPF All Designated Routers “”(DR)”” address is used to send OSPF routing information to designated routers on a network segment.
188.8.131.52 The Routing Information Protocol (RIP) version 2 group address is used to send routing information to all RIP2-aware routers on a network segment.
184.108.40.206 The Enhanced Interior Gateway Routing Protocol (EIGRP) group address is used to send routing information to all EIGRP routers on a network segment.
220.127.116.11 Protocol Independent Multicast (PIM) Version 2
18.104.22.168 Virtual Router Redundancy Protocol (VRRP)
22.214.171.124–21 IS-IS over IP
126.96.36.199 Internet Group Management Protocol (IGMP) version 3
188.8.131.52 Hot Standby Router Protocol version 2 (HSRPv2) / Gateway Load Balancing Protocol (GLBP)
MAC multicast address range of 01-00-5E-00-00-00 to 01-00-5E-7F-FF-FF
The limitation of number of MAC multicast address require that MAC to IP map for multicast is 32/2^5 to 1 maping. especially, the last 23 bits of IP or MAC address will be match.
IGMP will be used to make host able to join and leave multicast group
IGMP v1: to types of message : membership query and membership report
especially, router will send out membership query towards multicast ip 184.108.40.206. And host will send membership report towards the mulicast ip that host want to join.
Once router receives membership report from host via interface x, router will add interface x into the mroute table. Mroute table item can be timeout after, for example, 3 mins, if host does not want to join multicast group any longer host will stop sending membership report.The router will keep forwarding multicast traffic to the hosts until the timer expires.
Host is able to send membership leave message instead of letting multicast timeout in the router. Memembership leave message will be sent to general multicast ip 220.127.116.11
When hostx send membership leave message to router, router will issue a specific membership query message towards the interface where hostx sent leave message. This specific memebership query message will be sent towards the specific multicast address instead of generic 18.104.22.168 address.
when there is multiple routers in one network segment, there will be one router with lowest ip selected as active router to send membership query message
This feature will be used in switches, so switches will snoop IGMP traffic between hosts and routers, maintain a mulicast table (CAM table), each item in the table will contain multicast dest MAC adress and interfaces that should get traffic wich that multicast dest MAC.
On the switch, all multicast traffic that is IGMP traffic will be sent to core of switches to process, realtime mulicast traffic (not IGMP traffic) will not be forwarded to switch core, this will reduce the burden of switches core
In the scenario where there is no Router, in order to get multicast work, we can
1, configure one of the svi interface on the switch to send member query message
2, configure svi interface with pim sparse mode
3, use broadcast instead of multicast by disable igmp snoopint
4, configure static mrouter port
5, configure Static multicast entry
3, IP multicast routing protocol
There are 2 mode of multicast dense mode and sparse mode
mulitcast traffic will send to all of the interfaces of the router except for the interface where the traffic come in. If the other routers do not want the traffic (not get membership report message),routers need send ‘no this mutlicast traffic’ back to the orignal router
There are a number of dense mode routing protocols:
DVMRP (Distance Vector Multicast Routing Protocol)
MOSPF (Multicast OSPF)
PIM Dense Mode ( This is mostly used)
Dense mode will do RPF check (reverse path forwarding). router will check the source ip of the multicast traffic, if the source ip A is supposed to come in from portX on the router, the incoming traffic that comes from portY with source ip A will be dropped.
Dense mode floods multicast traffic until a router asks you to stop.
Sparse mode sends multicast traffic only when a router requests
In sparse mode, there will be a RP (Rendezvous Point), router who receive IGMP membership report message will send PIM join message to RP. Routers will find RP by static configuration or by dynamic learning.
For those routers who are not interested in multicast traffic and filter out all multicast traffic on the router.