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CCNP Core > Chap 13 - Multicast (part 3) > Flashcards

Chap 13 - Multicast (part 3) Flashcards

1
Q

When is PIM-SM used?

A
  • When there are only a few receivers throughout the network.
  • It also works well in densely populated networks
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2
Q

In PIM-SM when does PIM forward multicast traffic?

A
  • Receiver sends LHR a Join Request
  • Then PIM-SM router sends a PIM Join in the direction of the root of the tree which is either the Source or the RP
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3
Q

What does an RP do when it receives a Join request from the LHR?

A
  • Creates a Shared Tree in the direction of the LHR
  • Then sends a Join to the FHR
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4
Q

What is a Source Tree

A
  • SPT
  • Shortest Path Tree, (S, G)
  • Source is the root of the tree
  • Routers are leaves
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5
Q

What is a Shared Tree

A
  • RPT
  • Rendezvous Point Tree (*,G)
  • Packets forwarded down the tree based only on the Group IP address and regardless of the source
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6
Q

Once a RPT is created what can the LHR do by default?

A

Switch over to a SPT.

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7
Q

When does the SPT Switchover happen?

A

When the LHR receives the first multicast packet from the RP over the RPT and it becomes aware of the IP address of the source.

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8
Q

What happens in PIM when there are multiple routers on a single LAN?

A
  • A Designated Router election is held using Hello’s to determine which router will be the DR
  • Winner is router with highest DR priority
  • If priorities tie then highest IP address is the tie breaker.
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9
Q

What is the default DR Priority on Cisco routers?

A

1

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10
Q

On a FHR what is the DR responsible for?

A

Encapsulating in unicast register messages any multicast packets originated on the subnet destined for the RP

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11
Q

On a LHR what is the DR responsible for?

A
  • Sending PIM Join and Prune msgs to RP
  • Performs SPT switchovers
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12
Q

What is the default Designated Router Hold time?

A

3.5 times the Hello or 105 seconds by default

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13
Q

What is the default Hello interval?

A

30 seconds

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14
Q

What is Reverse Path Forwarding (RPF)?

A
  • An algorithm used to prevent loops
  • Ensures that multicast traffic is arriving on the RPF Interface
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15
Q

How does router know which interface is the RPF interface?

A

The RPF interface must be the same interface the router would use to send a unicast packet to the multicast source

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16
Q

What does a router do if it receives a multicast packet on its RPF interface?

A

The router forwards it out the interfaces on its Outgoing Interface List (OIL)

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17
Q

What does a router do and why if it receives a multicast packet on its non-RPF interface?

A

It discards the packet to prevent loops

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18
Q

If a router has a (S, G) in mroute which interface does a router perform a RPF check on

A

The IP address for the Source of the multicast packet.

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19
Q

If a router has no explicit source tree state how does router perform an RPF check?

A

If no explicit Source Tree state exists then the check is done on the address of the RP

20
Q

What does PIM use the RPF check for?

A

To determine where it needs to send joins, prunes. (S,G) joins are sent to the source, (*,G) joins are sent to the RP

21
Q

What does the Assert Mechanism do?

A

It prevents duplicate multicast flows on an ethernet network.

22
Q

Which PIM mode uses the Assert Mechanism?

A
  • PIM-DM and sometimes PIM-SM
  • Rarely used in PIM-SM.
23
Q

PIM forwarder is rarely used in PM-SM. Why?

A

The only time the PIM Forwarder is used in PIM-SM is when there is some kind of routing inconsistency.

24
Q

Can a PIM Bootstrap router and Auto-RP be used together?

A

No because it may introduce unnecessary complexities.

25
Q

In what Scenarios is Static RPs a good alternative?

A
  • Simple configuration (1 or 2 lines) on each router
  • If the network doesn’t need many RPs
  • If the RPs don’t change very often
  • If the network is small
26
Q

What is the downside to using Static RPs?

A
  • A lot of administrative overhead if the network is big
  • No load balancing
  • No failover process
27
Q

What are the 6 benefits to using Auto-RP?

A
  • Easy to use multiple RPs for different group ranges
  • Allows load-splitting
  • Simplifies RP placement according to locations of group participants
  • Prevents inconsistencies btw statically assigned RPs
  • Multiple RPs can serve different group ranges and be backups
  • Uses 2 basic components - Candidate RPs (C-RPs) and RP Mapping Agents (MAs)
28
Q

In Auto-RP, what is the default RP Announce Interval?

A

60 seconds

29
Q

What address do RP Announcements use?

A

224.0.1.39

30
Q

In Auto-RP, how does a Candidate RP make itself known?

A

Cisco-RP-Announce advertisements every 60 seconds

31
Q

What is in a Cisco-RP-Announce msg?

A
  • Default Group range 224.0.0.0/4
  • The C-RP’s address
  • Hold time (3 times the Announce interval
32
Q

What happens if there multiple C-RPs?

A

The one with the highest IP address wins.

33
Q

What Multicast address do C-RPs send Cisco-RP-Announce messages to?

A

224.0.1.39 (Cisco-RP-Announce)

34
Q

What are 3 things RP Mapping Agents do?

A
  • Joins: The MA joins 224.0.1.39 to listen to C-RP announcements
  • Selects: The MA saves info from C-RP announcements, selects C-RP with highest IP to be Active RP and adds that to a Group-to-RP mapping cache
  • Advertises: The MA then advertises the Group-to-RP mappings to all other PIM-enabled routers on 224.0.1.40
35
Q

Do RP Mapping Agents have the same info in their cache?

A

Yes, identical

36
Q

What is a PIM Bootstrap Router (BSR)?

A

It is a nonproprietary mechanism that provides a fault-tolerant, automated RP discovery and distribution mechanism.

37
Q

What is an RP Set and what 5 items are in it?

A
  • It is a BSR Group-to-RP mapping that contains
  • Multicast Group Range
  • RP Priority
  • RP Address
  • Hash mask length
  • SM/Bidir flag
38
Q

What can be done to prevent a single point of failure of BSRs?

A
  • Deploy multiple Candidate BSRs (C-BSR)
  • C-BSR with highest priority wins
  • If a tie then C-BSR with highest IP is elected
39
Q

When a BSR message is received does the PIM Router flood the message out the same interface it was received on?

A

Yes

40
Q

When a BSR message is sent what address is it sent to?

A

224.0.0.13 (All PIM address)

41
Q

What is the TTL for a BSR message?

A

1 hop

42
Q

Which Group-to-RP Mapping mechanism was developed by Cisco?

A

Auto-RP

43
Q

What is the difference between IGMPv2 and IGMPv3?

A

IGMPv3 introduced a new IGMP membership report with source filtering support.

44
Q

What is the correct term for what a receiver must do to receive multicast from a group?

A

Unsolicited Membership Report

45
Q

When is it mandatory to choose an RP?

A

What PIM-SM is used.

46
Q

For ASM (Any Source Multicast) what does the (S,G) require?

A

A parent (*,G)

47
Q

What is the difference between Designated Router (DR) and PIM Forwarder?

A
  • The PIM Forwarder is determined by the Assert mechanism. The router with the best AD, metric, or highest IP wins.
  • The Designated Router is chosen by exchanging Hello packets. The DR will have either the highest priority or the highest IP address in the subnet.

CCNP Core (46 decks)

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