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CCNP Core > Chap 13 - Multicast (part 1) > Flashcards

Chap 13 - Multicast (part 1) Flashcards

1
Q

What 2 components does Multicast rely on?

A
  • IGMP
  • PIM
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2
Q

What layer does IGMP operate at?

A

Layer 2

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3
Q

What layer does PIM operate at?

A

Layer 3

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4
Q

What is the MDT?

A

Multicast Distribution Tree

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5
Q

What address range has been assigned for Multicast?

A

224.0.0.0/4 to 239.255.255.255

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6
Q

What are the first 4 bits of the multicast range?

A

1110

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7
Q

What addresses does the Local Network Control Block contain?

A

224.0.0.0/24

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8
Q

What addresses does the Local Internetwork Control Block contain?

A

224.0.1.0/24

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9
Q

What is the address range of the Local Network Control Block, what is it used for, and what are 3 examples?

A
  • 224.0.0.0/24
  • Used for protocol control traffic that is not forwarded outside of a broadcast domain
  • All hosts use 224.0.0.1
  • All routers use 224.0.0.2
  • All PIM routers use 224.0.0.13
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10
Q

What is the range of the Internetwork Control Block, what is it used for, and what are 3 examples?

A
  • 224.0.1.0/24
  • Used for protocol control traffic that may be forwarded through the Internet
  • NTP uses 224.0.1.1
  • Cisco-RP-Announce uses 224.0.1.39
  • Cisco-RP-Discovery uses 224.0.1.40
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11
Q

What does SSM stand for and what is it?

A
  • Source Specific Multicast
  • PIM extension
  • Forwards traffic to receivers from only those sources that receivers have expressed interest
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12
Q

What address range is used by Source Specific Multicast Block?

A

232.0.0.0/8

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13
Q

What address range is used by the GLOP Block?

A

233.0.0.0 to 233.251.255.255

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14
Q

What is the scope of the GLOP Block, what address range is it, what does it provide for, and who can use it?

A
  • Global in scope
  • 233.0.0.0 to 233.251.255.255
  • Provides for statically assigned addresses by mapping an organizations ASN number into the 2nd and 3rd octets of a multicast address.
  • For domains with 16-bit ASN numbers
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15
Q

How are ASNs mapped into the GLOP Block?

A
  • Maps a domains 16-bit ASN number into the middle two octets
  • 233.x.y.0/24 where x and y contain 8 bits each of the 16-bit ASN.
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16
Q

What 2 alternatives does an organization who wants an address from the GLOP Block but their ASN is 32-bits?

A
  • Take an assignment from the Ad hoc range
  • Consider IPV6 Multicast Addresses
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17
Q

What address range has been assigned for the Administratively Scoped Block?

A

239.0.0.0/8

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18
Q

What address range is the Administratively Scoped Block, what is its scope, what can it be compared with, who can use it, and what is it typically used for?

A
  • 239.0.0.0/8
  • Scope is private
  • Similar to private IP addressing (RFC1918)
  • Network administrators are free to use this address range but only in their domain
  • Typically used by SSM even though SSM has its own block
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19
Q

What does the first 24 bits of a Multicast MAC address start with?

A

01:00:5E

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20
Q

What are the components of a Multicast MAC address?

A
  • bits 1 to 24 - 01:00:5E
  • bit 25 is multicast bit always set to 0
  • The last 23 bits are copied directly from the multicast IP address
  • This leaves the possibility of 32 overlapping addresses
21
Q

Where in a Multicast MAC address is the Multicast/Broadcast bit and what should it be set at?

A
  • Low order bit of the first 8 bits
  • Set to 1 for multicast (or broadcast)
22
Q

What does a receiver do when a receiver wants to receive a specific multicast feed?

A
  • Sends an Unsolicited Membership Report (aka IGMP Join) using the multicast IP address of that group.
  • Reprograms its NIC to accept the multicast MAC group address that correlates to the group IP address
23
Q

What protocol do receivers use when they want to join multicast groups and receive traffic from that group?

A

IGMP

24
Q

What is IGMP, where is it enabled and how many versions are there?

A
  • Internet Group Management Protocol
  • Needs to be enabled on receiver and router
  • There are 3 versions
25
Q

What is the TTL for an IGMP packet?

A

1

26
Q

What are the 5 different IGMP message along with their types numbers?

A
  • Ver 2 Membership Report - 0x16
  • Ver 1 Membership Report - 0x12
  • Ver 2 Leave Group - 0x17
  • General Membership Query - 0x11
  • Group Specific Query - 0x11
27
Q

What are the 4 fields in an IGMP message?

A
  • Type
  • Max Response Time
  • Checksum
  • Group Address
28
Q

What is the IGMP Type for a Ver 2 Membership Report, and when are 2 times when it is used?

A
  • 0x16
  • aka IGMP Join message
  • used by receivers to join a Multicast group
  • Also used by receivers to respond to local router’s Membership Query
29
Q

What is the IGMP Type for the Ver 1 Membership Report, and what does this message type allow for?

A
  • Type 0x12
  • Provides backward compatibility with IGMP V1
30
Q

What is the IGMP Type for a Ver 2 Leave Group message and when is this sent?

A
  • Type 0x17
  • Used by receivers to indicate they want to leave a group they previously joined
31
Q

What is the IGMP Type for a General Membership Query, what is the destination address what is the group address?

A
  • Type 0x11
  • Sent to the all-hosts Group Address (224.0.0.1)
  • Used to check if there are any Receivers in the attached subnet
  • Sets Group Address to 0.0.0.0
32
Q

What is the IGMP Type for Group Specific Query, when is it sent, what is its destination set to?

A
  • Type 0x11
  • Sent in response to a Leave Group message
  • Sent to the Group Address that the Receiver wants to leave
  • Destination IP address of this is the Group IP address and also in the Group Address Field
33
Q

What is the IGMP Field Max Response Time, when is it used, and what is it’s unit of measurement?

A
  • Specifies maximum amount of time a receiver has before it must reply with a Membership Report message
  • Used only in General Membership Query and Group Specific Query
  • In any other type of message value is set to 0x00 and ignored by Receivers
  • Units of one tenth of 1 second
34
Q

How many bits in the IGMP Field Checksum and how is the checksum calculated?

A
  • 16 bits
  • Set to 1’s complement of the 1’s complement sum of the message
  • Standard checksum method used by TCP/IP
35
Q

What is the IGMP Field Group Address used for in a General Query message, Group Specific Query, Membership Report and Leave Group messages?

A
  • In General Query messages is set to 0.0.0.0
  • In Group Specific messages is set to the Group Address
  • Membership and Leave messages have the Group Address being joined or left
36
Q

What 4 things does a router do when it receives a Membership report?

A
  • Router forwards the request in a PIM Join Message
  • When router starts receiving the stream it forwards it to the Subnet where the Join message came from
  • Router then starts sending periodic General Membership Queries to the subnet using 224.0.0.1 to see if there are any members in the attached subnet
  • These general query messages have Max Response Time set to 10 seconds by default
37
Q

What is the default Max Response Time in a General Membership Query?

A

10 seconds

38
Q

What does a Receiver do when it receives a General Membership Query?

A
  • Sets an internal random timer between 0 and 10 seconds
  • When timer expires Receiver sends Membership Reports for each group it belongs to
  • If Receiver sees a Membership Report from another Receiver it stops its timer for the specified group
  • This is meant to suppress duplicate Reports
39
Q

What does a Receiver do when it wants to leave a group?

A
  • If the Receiver was the last to respond to the latest General Membership Query it sends a Leave Group message to 224.0.0.2 (AllRouters)
  • If it wasn’t the last to respond it can leave the group quietly because there are other Receivers on the subnet
40
Q

How does a router know if there are any Receivers left on the subnet after having received a Leave message?

A
  • Router sends a Group Specific Query to see if there are any Receivers left who are interested in the group
  • If none then router removes the IGMP state for that group
41
Q

What happens if there is more than one router on a subnet?

A
  • IGMP Querier Election takes place
  • Routers send General Membership queries to 224.0.0.1
  • Routers check each other’s source IP addresses
  • Router with lowest interface address on the LAN wins
42
Q

What 3 things happen after the IGMP Querier election?

A
  • Non-querier routers set timers that reset each time they receive a General Membership Query Report from the Querier
  • If Querier stops sending Membership Query Reports the router waits 120 seconds (twice the default 60 second query interval)
  • If still no Membership Query Reports the router will trigger another Querier Election
43
Q

In IGMPv2 can a Receiver specify the source it would like to use when it sends the IGMP Join message?

A

No, but IGMPv3 allows for that.

44
Q

What are 2 things IGMPv3 does and 2 things that it added that are different than IGMPv2?

A
  • IGMPv3 allows Receivers to specify the Multicast source
  • V3 is backward compatible
  • V3 added new fields to the IGMP Membership Query
  • V3 added a new message type called Ver 3 Membership Report to support source filtering
45
Q

In IGMPv3 what are the 2 modes a Receiver can use when signaling they want to join a multicast group?

A
  • Include mode - Receiver sends join message that includes a list of sources it wants to receive Multicast from
  • Exclude mode - Receiver sends join message listing sources it does NOT want multicast from
46
Q

In IGMPv3 what does the Receiver do if it doesn’t care which source it uses for multicast?

A

Receiver uses Exclude mode and leaves the Exclude list empty

47
Q

What 2 methods does Cisco use to prevent switches from flooding multicast frames out all ports?

A
  • IGMP Snooping
  • Static MAC address entries
48
Q

How does IGMP Snooping work?

A
  • Switch watches for group-specific IGMP Joins and adds that information to the MAC address table
  • When the switch sees multicast traffic for a specific group it forwards it out only on interfaces where it saw the IGMP join for that group
49
Q

Does IGMP Snooping prevent all flooding on switches?

A

No, some multicast addresses are still flooded

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