Multicast CCIE-ENTERPRISE-INFRASTRUCTURE Practice Questions (Page 6)

Questions 26–30

1. 26expert · hard

   In a PIM-SM network, a last-hop router is receiving a high-bandwidth stream via the shared tree. The administrator wants to reduce latency and core router load by switching to the SPT, but they are concerned about the burst of join messages and the potential for packet loss during the switchover. What is the best practice to minimize disruption?

   • ASet the SPT threshold to 0 to switch immediately, and rely on the multicast source's buffering.
   • BPre-build the SPT by configuring a static (S,G) route on the last-hop router.
   • CSet the SPT threshold to a value that triggers switchover only when the traffic rate is consistently high.
   • DUse PIM-DM for this group to avoid the shared tree entirely.
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2. 27expert · hard

   A network engineer is troubleshooting a multicast issue where packets from a source are being dropped on a router. The unicast route to the source is via a default route (0.0.0.0/0) pointing to a WAN interface. The multicast packets arrive on a different interface. What is the likely outcome of the RPF check?

   • AThe RPF check is bypassed for sources that are not in the unicast routing table.
   • BThe RPF check fails because the incoming interface does not match the interface used to reach the source via the default route.
   • CThe RPF check passes because the default route is considered a valid reverse path for any source.
   • DThe RPF check passes because the default route is used as a fallback.
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4. 28expert · hard

   A network has both Auto-RP and BSR configured. The administrator notices that some routers are using an RP that is not the one intended. What is the most likely cause?

   • AThe RP is not reachable via unicast, so routers fall back to a different RP.
   • BAuto-RP and BSR are both distributing RP information, and the routers are using the first RP they learn.
   • CBSR is always preferred over Auto-RP, so the intended RP is ignored.
   • DAuto-RP is disabled on the RP, so BSR is the only source of RP information.
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5. 29expert · hard · select all that apply

   A network administrator is troubleshooting a multicast issue where hosts in VLAN 20 are not receiving a stream that is working in VLAN 10. The switch has IGMP snooping enabled. Which of the following could be the cause? (Select all that apply.)

   • AThe multicast MAC address is not in the CAM table for VLAN 20.
   • BThe switch is not configured with MVR, so multicast cannot cross VLANs.
   • CIGMP snooping is disabled on VLAN 20.
   • DThe host's IGMP membership report is not being processed because the querier is not on VLAN 20.
   • EThe router port for VLAN 20 is not configured as a multicast router port.
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6. 30expert · medium

   In a PIM-DM network, a new multicast source begins transmitting. The network has a redundant topology. What is the initial behavior of PIM-DM?

   • ARouters wait for an IGMP report before forwarding any multicast traffic.
   • BRouters use the RP to build a shared tree first.
   • CRouters send explicit join messages toward the source to build a tree.
   • DRouters flood the multicast packets out all interfaces, and then prune the branches with no receivers.
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