Multicast Flashcards
What is the purpose of multicast
To send traffic throughout the network to many receivers on a one-to-many model.
Why use multicast over unicast or broadcast traffic when sending from one source to many receivers
AS with unicast each receiver will need its own traffic stream and broadcast will send the traffic to every host regardless of whether that host wants to receive or not. Both unicast and broadcast will use A LOT of bandwidth in this case. therefore using multicast preserves bandwidth and system resources.
What protocols does multicast require for its operation
IGMP and PIM.
What is the reserved range for multicast address’
224.0.0.0 - 239.255.255.255 Class D address
What is the ‘administratively scoped’ block of the multicast range address and purpose
239.0.0.0 to 239.255.255.255. the purpose is similar to private addressing (RFC1918) and is limited to a single organisation.
What are the ‘local’ and ‘internetwork’ control block multicast address ranges and purpose.
Local control block: Used for multicast protocol traffic within a broadcast domain. e.g. OPSF,EIGRP,RIP & PIM routers
Internetwork control block: Used for multicast protocol traffic that leaves the broadcast domain. e.g. NTP, cisco RP announce/discovery.
What are the well-known multicast address’
224.0.0.0 - Base address
224.0.0.1 - All hosts on subnet
224.0.0.2 - All routers
224.0.0.5 - OSPF routers
224.0.0.6 - OSPF DR routers
224.0.0.9 - RIP
224.0.0.10 - EIGRP
224.0.0.13 - PIM routers
224.0.0.18 - VRRP
224.0.0.22 - IGMP
224.0.0.102 - HSRPv2 & GLBP
224.0.1.1 - NTP
224.0.1.39 - Cisco RP announce
224.0.1.40 - Cisco RP discovery
What is the purpose of a multicast MAC address and how is it Identified
Each group address has a MAC address starting 01:00:5E, the first 25 bits are fixed. The group gets a multicast MAC to avoid having to alter packets.
What is IGMP and what is the purpose of the protocol
Internet Group Management Protocol (IGMP) is a protocol used by multicast receivers to join a multicast group and start receiving traffic from the group.
What IP protocol number is IGMP
IP protocol number 2
For IGMP to work, where must the protocol be supported
The receiver
the interface of the router facing the receiver
When a receiver wants to join a multicast group the receiver will send an IGMP join to the router. if the router does not have IMGP enabled the packet is discarded.
True or False
True.
What is the official term used for an IGMP join
IGMP version 2 membership report
What is the difference between IGMP version 1,2 & 3
Version2 allowed the receiver to leave the multicast group
Version 3 allowed source specific multicast (SSM) which allow the receiver to pick the source they receive the traffic from.
What are the different message types used in IGMP
version 2 membership report: same as IGMP join
version 1 membership report: allows backward compatibility with version 1
version 2 leave group: Allows receiver to leave group
General membership query: periodically sent to all hosts to see if any hosts are attached to the subnet
Group specific query: sent in response to a leave request to check if any other hosts on the subnet want to receive the multicast traffic. If no answer then IGMP state is stopped for that subnet.
What is the IGMP max response time and default value
the time waiting before sending a response to the general membership/ group specific query.
What is the process if there are multiple IGMP enabled router interfaces on the same LAN segment.
The router will compare the IP address when sending a general membership report.
The interface with the lowest IP address wins the election.
What happens to the loosing router in the IGMP election
It waits the 2x query time 60 seconds by default, before starting the election again.
What are the 2 modes for IGMPv3
Include and exclude, this allows you to either include source address’ or exclude them.
What is IGMP snooping
When a switch doesn’t know the MAC address it sends it out all switchports apart form the one it received it on. With snooping the switch only sends it out switchports that have had a IGMP join received on that interface.
What is PIM
Receivers will used IGMP to connect to a source if they are on the same LAN if they are on different LANs a multicast routing protocol is required to get the traffic from source to receiver.
PIM is the protocol to perform this action and is a Cisco protocol.
PIM is protocol independent for identifying the best path between FHR and LHR
True or False
True: PIM can use any of the unicast routing protocols or static routing to identify the best path.
What is a PIM distribution tree
it is a method of showing the path multicast traffic takes form source to receiver.
the 2 types are:
1. Source tree / shortest path tree (SPT)
2. Shared tree / RP trees.
What is the forwarding state of a SPT/source tree
It will be in the notation (S,G) where the S is the source IP address for the multicast source and the G is the multicast group address. Each source will require a separate entry in the MRIB (S,G).
What is a shared tree and what is the forwarding state of the tree
A shared tree is different as the root of the tree is the RP. PIM routers will have an entry in the MRIB of (*,G) which the * indicates any source. the traffic will be forwarded to the RP which then goes across a PIM tunnel to the source.
What is the different modes of PIM
PIM-DM
PIM-SM
PIM sparse dense mode
PIM-SSM
PIM-bidir
What IP protocol number does PIM use for control messages
103
How are other PIM routers discovered
PIM enabled routers will send out hello messages at default every 30 seconds to the all PIM routers address 224.0.0.13.
