IPv4 Multicast Flashcards
What is multicast?
Multicast is a type of group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution.
In other words, a single packet can be forwarded on to multiple other endpoints or networks.
What is the IPv4 address range for multicast addresses?
The 224.0.0.0/4 address block (224.0.0.0 - 239.255.255.255)
What is IGMP?
Internet Group Management Protocol - the protocol a host endpoint will use to join a Multicast group. This occurs within a given VLAN/network for hosts to tell their routers they want to listen for Multicast traffic.
What is a multicast group?
An IP address that will specify a one-to-many relationship for data transfer. Endpoint hosts will request to join a multicast group via IGMP.
In multicast, what is a receiver?
A host that is looking to subscribe to a multicast group.
In multicast, what is a stream?
The data packets that are being sent to a multicast group.
What is an MDT?
Multicast Distribution Tree
In a Multicast Distribution Shared Tree, what is an RP?
Rendezvous Point - the starting point or Trunk of the tree.
In Multicast, what is PIM?
Protocol Independent Multicast - this is the router-to-router communication to negotiate multicast neighbors.
In Multicast distribution, what is a SPT?
Shortest Path Tree - when routers negotiate a multicast path that is a more direct path than traversing the shared tree.
What are the three types of Multicast Modes?
Dense Mode
Sparse Mode
Source Specific Multicast (SSM)
How does Multicast Dense Mode function?
The router just sends multicast messages to all of its PIM neighbors. When a network or neighbor doesn’t want the traffic, it will send back “Prune” messages to stop it.
This is the least popular type of Multicast mode
How does Sparse Mode function?
It uses a Rendezvous Point, IGMP, and PIM to negotiate multicast distribution trees (shared or shortest path)
In multicast, what are the FHR and the LHR?
First Hop Router - attached to the source LAN
Last Hop Router - attached to the receiver LAN
What is the formal name of a “Join” message?
IGMP Membership Report
How does SSM (Source Specific Multicast) function?
When a client knows the source of a multicast and wants to subscribe to that multicast group via IGMP.
In multicast, what is RPF?
Reverse Path Forwarding - an algorithm used to prevent loops and ensure that multicast traffic is arriving on the correct interface.
What are the commands to enable multicast sparse mode on a router and enable IGMPv3?
Router(config)# ip multicast-routing distributed
Router(config)# int gi0/1
Router(config-if)# ip pim sparse-mode
Router(config-if)# ip igmp version 3
Router(config)# ip pim rp-address <ip></ip>
What feature does IGMPv3 contain that makes it the desired protocol to configure on an interface?
Multicast source filtering
What is the biggest difference between IGMP and PIM?
IGMP functions on the LAN where the endpoints are located. PIM functions between routers.
What does it mean when a Multicast address has zeros in the second and third octet (i.e. 224.0.0.22)?
This is a local segment only address that cannot be routed.
What command would you use to show the multicast routing table on a Cisco device?
show ip mroute
What command would you use to verify IGMP on an interface?
show ip igmp interface <interface></interface>
What command would you use to verify multicast neighbors?
show ip pim neighbors
What is the 232.x.x.x IPv4 octet designated for?
Source Specific Multicast; However, this is not a requirement for SSM
On what device in the network does IGMP Snooping occur?
Switch (Layer 2)
What does IGMP Snooping do?
It prevents multicast from being sent to hosts on a LAN segment that do not want it. (Preserving bandwidth)
What is Auto-RP?
A Cisco mechanism for multicast that performs group-to-RP mapping
What is the range of multicast addresses that are reserved for the local network control (not forwarded from the broadcast domain)?
224.0.0.0/24
What is the range of multicast addresses that are reserved for the Internetwork network control (may be forwarded through the Internet)?
224.0.1.0/24
Note: NTP uses this on 224.0.1.1
What multicast address means “all hosts in this subnet”?
224.0.0.1
What multicast address means “all Routers in this subnet”?
224.0.0.2
What multicast address means “all OSPF Routers” ?
224.0.0.5
What multicast address means “all OSPF DRs (OSPFDRouters)”?
224.0.0.6
What multicast address means “all RIPv2 Routers”?
224.0.0.9
What multicast address means “all EIGRP Routers”?
224.0.0.10
What multicast address means “all PIM Routers”?
224.0.0.13
What multicast address is for VRRP?
224.0.0.18
What multicast is for IGMPv3?
224.0.0.22
What multicast address is for HSRP and GLBP?
224.0.0.102
What multicast address is for NTP?
224.0.1.1
What multicast address is for Cisco-RP-Announce (Auto-RP)?
224.0.1.39
What multicast address is for Cisco-RP-Discovery (Auto-RP)?
224.0.1.40
What multicast address range is reserved for SSM?
232.0.0.0/8
What multicast address range is reserved for GLOB (Globally scoped assigned)?
233.0.0.0/8
What multicast address range is reserved for Administratively assigned (i.e. private use) via RFC 2365?
239.0.0.0/8
What are the first 24 bits of any Multicast MAC address?
01:00:5e
How is a multicast address converted to the Multicast MAC?
The first 24 bits of a multicast MAC address always start with 01:00:5E. The low-order bit of the first byte is the individual/group bit (I/G) bit, also known as the unicast/multicast bit, and when it is set to 1, it indicates that the frame is a multicast frame, and the 25th bit is always 0. The lower 23 bits of the multicast MAC address are copied from the lower 23 bits of the multicast group IP address.
What is IGMP?
Internet Group Management Protocol - the protocol used by network devices to JOIN multicast groups.
NOTE: IGMP is not responsible for the routing of Multicast Traffic.
What is the protocol number for IGMP?
Protocol 2
What are the 8 types of IGMP message format fields?
- Version 2 Membership report (aka Join)
- Version 1 Membership report
- Version 2 leave group
- General Membership Query
- Group Specific Query
- Max Response Time
- Checksum
- Group Address
What is the key difference between IGMPv2 and IGMPv3?
IGMPv3 extended IGMPv2 by adding source filtering. IGMPv3 is backwards compatible with IGMPv2 and IGMPv1.
What are two methods Cisco switches use to reduce multicast flooding on a LAN segment?
- IGMP Snooping
- Status MAC Address Entry
