multicast flashcards 1
Range mac address Multicast
01:00:5e:00:00:00 – 01:00:5e:7F:FF:FF
Protocols interdomain Multicast
MSDP / MP BGP
Consists of setting a TTL to define a forwarding scope. TTL Thresholds can be configured to prevent packets with a TTL less than the defined one from being forwarded
Multicast scoping. There are problems for the use case of Flood and Prune protocols, if a router discards by TTL it does not generate a prune message to force traffic to stop
Protocols used in the receiver register in IPv4 and IPv6
IGMP or MLD is used for registration between Receiver and LHR, there are no protocols for Sender x FHR communication
Dense mode protocols
PIM DM, DVMRP
Protocol that operates in Flood and prune
PIM DM
Protocol that uses Prune messages and Assert are used for the formation of the Shortest Path Tree
PIM DM
Protocol that operates with implicit join. Protocol that operates with explicit join
PIM Dense, PIM Sparse mode
PIM messages: Join - Messages for a router to join a distribution tree, a multicast group, and start receiving flows. Prune - Used to remove interfaces from a tree and then stop receiving flows. Graft - When a router has already sent prune messages but wants to join a tree again
Join, Prune, Graft
BGP does not build a multicast distribution tree, so Multicast Source Discovery Protocol (MSDP) is necessary
BGP, Multicast Source Discovery Protocol (MSDP)
Multicast Source Discovery Protocol (MSDP) distributes information about the existence of sources in each AS. When routers discover the existence of active sources in another domain, PIM (S,G) messages are sent to interconnect sources and receivers. Allows RP to announce their sources (S,G) using source-active messages. Basically, RPs establish sessions and announce sources. Also used in environments with Anycast RP intra-AS
Multicast Source Discovery Protocol (MSDP)
Which routers should establish MSDP sessions?
The RPs, as they should announce their sources
If a router learns an RP dynamically and has a static configuration, then the static RP is preferred
False, the dynamic RP is preferred
What will be the composition of the MAC address for the multicast address 239.255.8.5?
First, convert the IP multicast address 239.255.8.5 to binary form: 1110 1111.1111 1111.0000 1000.0000 0101. Next, separate the 23 low-order binary bits from the converted address: 1110 1111.1111 1111.0000 1000.0000 0101. Drop other bits: 111 1111.0000 1000.0000 0101. Convert these bits to hexadecimal: 7F.08.05. We know that the first 24 bits of this MAC address always begin with 01.00.5e (the organizationally unique identifier or OUI). So we just need to append the converted result with 01.00.5e to get the result: 01.00.5e.7F.08.05. That is the official way to convert a multicast IP address to a multicast MAC address. There is a shorter way to do this: Convert the 3rd and 4th octet directly to hex. If the decimal value of the 2nd octet is greater than 128, then subtract it by 128 and convert it to hex. If not, convert it directly to hex. Append your results with 01.00.5e.
Which protocols are used to join a multicast group? Which of them does not generate *,G entries?
IGMP v1 v2 v3, v3
Source tree, Shared tree
Uses IGP best path from sender to receiver, Uses the shortest path from sender to RP and shortest path from RP to receiver
Compare IGMPv1 and IGMPv2
v2 introduced the leave message
Which IGMP version is used in Source Specific Multicast?
IGMPv3
IGMPv3 does not require RP
True
What is the mechanism for preventing multicast loops?
uRPF
Which multicast protocol is suitable for Many-to-many applications?
BIDIR-PIM - Suitable when at the same time a sender can be a receiver and a receiver can be a sender, hence the need to be bidirectional
SSM is a variation of PIM-SM that builds only Source-specific SPT and does not need an active RP
SSM
In SM, multicast traffic is forwarded using S,G. If not, it uses *,G
True
PIM Shared Tree Join: Receiver originates an IGMP Report message to the LHR. The LHR sends PIM Join messages towards the RP. During this process, the shared tree is built
IGMP Report, Join
PIM SM Sender Registration: The source sends a multicast message to the FHR. The FHR encapsulates the multicast packet in a unicast register message and sends it to the RP. Unicast register? Multicast register?
Unicast register
In Cisco routers, the default SPT Threshold is 10 seconds. After this time, the router receives messages via the shared tree but containing the source (S,G), the LHR already sends join messages directly to the source
False - In Cisco routers, the default SPT Threshold is 0, so as soon as the router receives the first message via the shared tree but containing the source (S,G), the LHR already sends a join message to the source
PIM messages are encapsulated with protocol 104
False - 103
PIMv2 packets: PIM Hello (PIMv1 query messages) are used for neighbor discovery and maintenance. Sent every 30 seconds to 224.0.0.13. The options field contains the address of the DR
30, 224.0.0.13
PIM messages: Register - Register sources with the RP. Register stop - Originated by the RP to the FHR to stop encapsulating multicast messages in unicast register and start sending only multicast
Register, Register stop, Register
PIM Messages: Candidate RP - These are messages to announce candidate RP routers. The BSR collects information about the RP and distributes it in PIM bootstrap messages that are also used to elect the BSR. Also used in the PIM Auto RP mechanism. PIM RP Reachability message - Used by the RP to report its reachability to all nodes in the shared tree
Candidate RP, PIM bootstrap
