13. Multicast Flashcards
What is Multicast?
A technology that optimizes network bandwith utilization and conserves system resources. Called one-to-many
What are the protocols for Multicast?
IGMP for layer 2
PIM for layer 3
What are the 2 disadvantages of Broadcast?
- Not enabled by default on Cisco, enabling exposes to DDoS
- Nic’s of uninterested workstations must still process the broadcast packets
How does Multicast traffic operate?
Provides a single data packet that is replicated between links as the data forks on a network device along the Multicast Distribution Tree (MDT). A network device requests to receive the stream.
What is the multicast address range?
224.0.0.0 up to 239.255.255.255. First bits always start with 1110
What is the designation of the range 224.0.0.0/24?
Local network control block
What is the designation of the range 224.0.1.0/24?
Internetwork control block
What is the designation of the range 232.0.0.0/8?
Source Specific Multicast block
What is the designation of the range 233.0.0.0/8?
GLOP block
What is the designation of the range 239.0.0.0/8?
Administratively scoped block
Where does the 24-bits Multicast MAC starts with?
01:00:5E
Which bit is always 0 and wich always 1 with Multicast?
The 25th bit is always 0
The 8th bit is always 1
How are the lowest 23 bits calculated?
Copied from the Multicast IP
How does a receiver request for a specific Multicast feed?
It sends a IGMP join using the multicast IP for that feed. The receivers reprograms the interface with the corresponding MAC address
What is IGMP?
Internet Group Management Protocol. Used by receivers to join and start receiving traffic from multicast groups.
How many versions of IGMP are there?
3 versions
What is the IGMPv2 process?
- Receiver send IGMP join to local router with wanted group
- Router forwards upstream with PIM
- Stream begins
- Router sends periodically membership query messages with max timer
- Receivers waits timer and sends a membership report
- If a receiver receives a report whilst the timer is running it prevents sending duplicate reports
- Receiver that wants to leave ssends a message to 244.0.0.2 if it was the last receiver to respond
- Router sends a memberships query to the group multicast to see if there are still receivers left. If not it removes the IGMP state for the group
What happens when there are more IGMPv2 routers in the LAN segment?
A querier election takes place. General membership message are send to 244.0.0.1. Lowest IP wins.
A timer reset when memberships queries are received.
What happens when querier routers stops sending queries?
Non-querier routers wait twice the wait tie (default 60 sec). If nothing comes the election begins again.
What are the 5 IGMPv2 messages?
V2 membership report - join V1 membership report - backwards v2 V2 leave group - leave General membership query - 224.0.0.1 check members Group specific query - Reply to leave
What are the 2 extra modes of IGMPv3?
Include and exclude
What is IGMP snooping?
The switch rememers the interfaces from where the join messages came from
What is PIM?
Protocol Independent Multicast, the only multicast protocol Cisco supports.
What are the 2 types of distribution trees?
Source trees (SPT, shortest path tree) Shared trees (RPT, rendezvous point tree)
How do multicast routers reach the receivers?
Multicast routers create distribution trees that define the past IP multicast traffic follows
How do source trees work?
The source (Server) is the root of the tree and the branches form the distribution tree. Know as Source comma Group.
How do shared trees work?
The root is a router designated as the rendezvous point
What is the Reserve Path Forwarding (RPF) interface?
Interface with the lowest metric to the IP address of the source (SPT) or RP. Even equal the highest IP.
What is the RPF neighbor?
The PIM neighbor on the RPF interface
What is the upstream interface?
The interface towards the source of the stream, also known as incoming interface.
What is the downstream interface?
The interface backwards the source of the stream, also known as outgoing interface, also known as outgoing interface
What is the outgoing interface list?
Group of OIFs that are forwarding multicast traffic to the same group.
What is the last hop router (LHR)?
The router that is directly attached to the receiver. Known as the leaf router.
What is the first hop router (FHR)?
The router that is directly attached to the source. Responsible for sending register messages to the RP.
What is the Multicast Routing Information Base (MRIB?
Topology table which derives from the unicast table and PIM
What is the Multicast Forwarding Information Base (MFIB?
Uses the MRIB for faster hardware forwarding
What are the 5 PIM operating modes?
PIM Dense mode PIM Sparse mode PIM Sparse Dense PIM Source Specific Multicast PIM Bedirectional Mode
What is the protocol number of PIM?
103
What type are the control messages of PIM?
Unicast (register and register stop messages)
Multicast (TTL 1 to 244.0.0.13)
What is the default time for PIM Hellos?
30 seconds
What are the 9 types of PIM messages?
Hello Register Register stop Join/prune Bootstrap Assert Candidate RP advertisement State Refresh DF election
