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350-601 · Question #66

How do multicast routes in the same segment choose the DR?

The correct answer is D. PIM hello messages are sent to 224.0.0.13 and router with the highest priority is selected as the. In a multicast-enabled segment, PIM elects a Designated Router (DR) by sending hello messages to 224.0.0.13, with the router possessing the highest PIM priority (or highest IP address in case of a tie) being selected as the DR.

Network

Question

How do multicast routes in the same segment choose the DR?

Options

  • APIM exchanges unicast hello messages between all routers advertised by the any cast RP.
  • BCisco Nexus stitches do not have a concept of DR due to vPC.
  • CPIM hello messages are sent to 224.0.0.13 and the router with the lowest priority is selected as
  • DPIM hello messages are sent to 224.0.0.13 and router with the highest priority is selected as the

How the community answered

(67 responses)
  • A
    6% (4)
  • B
    1% (1)
  • C
    3% (2)
  • D
    90% (60)

Why each option

In a multicast-enabled segment, PIM elects a Designated Router (DR) by sending hello messages to 224.0.0.13, with the router possessing the highest PIM priority (or highest IP address in case of a tie) being selected as the DR.

APIM exchanges unicast hello messages between all routers advertised by the any cast RP.

PIM Hello messages used for DR election are sent using multicast, not unicast, to establish and maintain adjacencies on a segment.

BCisco Nexus stitches do not have a concept of DR due to vPC.

Cisco Nexus switches fully support PIM and the DR concept; vPC operates at Layer 2 and does not eliminate the need for a DR for Layer 3 multicast forwarding.

CPIM hello messages are sent to 224.0.0.13 and the router with the lowest priority is selected as

While PIM Hello messages are indeed sent to 224.0.0.13, the DR election process selects the router with the highest PIM priority, not the lowest.

DPIM hello messages are sent to 224.0.0.13 and router with the highest priority is selected as theCorrect

PIM Designated Router (DR) election occurs on a multi-access segment where multiple PIM-enabled routers are present; these routers exchange PIM Hello messages on the 224.0.0.13 multicast address, and the router with the numerically highest PIM priority value is elected as the DR, with the highest IP address breaking ties.

Concept tested: PIM DR election process

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-3s/imc-pim-xe-3s-book/imc-cfg-pim.html

Topics

#Multicast Routing#PIM#Designated Router (DR)#Network Protocols

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