An engineer is troubleshooting slow performance issues on a customer's network after the last multicast configuration change was applied on it. While checking the running configuration on the router,

Question

Options

• AConfigure ip igmp static-group command on all interfaces
• BRemove ip igmp join-group command on all unnecessary interfaces
• CConfigure all router interfaces to be process-switched by increasing the query interval
• DRemove unnecessary members from the IGMP group

• A
  11% (4)
• B
  71% (27)
• C
  3% (1)
• D
  16% (6)

Explanation

Option B is correct because ip igmp join-group causes the router itself to become a multicast group member, forcing the router's CPU to receive and process every multicast packet for those groups - having many such commands across multiple interfaces directly explains the high CPU utilization, and removing the unnecessary ones eliminates the root cause.

Option A is wrong because ip igmp static-group is indeed the better alternative (it forwards multicast without the router joining as a host), but simply adding it on all interfaces doesn't remove the offending join-group commands that are already causing the problem.

Option C is wrong because process-switching and IGMP query intervals are unrelated to this issue; in fact, switching to process mode would make CPU performance worse, not better.

Option D is wrong because removing IGMP group members refers to end-host membership changes, not to the router's own configuration - the problem is on the router, not on downstream hosts.

Memory tip: Think of join-group as the router crashing the party - it joins as a full participant and must process every packet itself (high CPU). static-group makes the router a doorman - it forwards traffic out the interface without personally consuming it. If your router is sweating, it's probably a party crasher.

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