What is the default action taken by an Alcatel-Lucent 7750 SR when it receives a packet addressed to a broadcast destination?

A router, by its fundamental design, operates at Layer 3 and serves as a boundary for Layer 2 broadcast domains. When a Nokia 7750 SR, acting in its routing capacity, receives a packet with a Layer 3 broadcast destination address (e.g., 255.255.255.255 or a directed broadcast), its default behavior is to not forward the packet to any other interface. This is a core principle of IP routing that prevents broadcast storms from propagating across an entire network. The router will process the packet locally if it is the intended recipient (for example, for a routing protocol), but it will not route it onward. Therefore, from a forwarding perspective, the packet is dropped.

B. Forwarding the packet is incorrect as this would violate the router's role as a broadcast domain boundary, potentially leading to network-wide broadcast storms.

C. This describes the behavior of a Layer 2 switch within a single broadcast domain (VLAN), not the default Layer 3 function of a router.

D. Flooding a packet back out the port it was received on is incorrect behavior for any standard networking device and would create network loops.

1. Nokia 7750 SR OS Router Configuration Guide, Release 22.10.R1: In the "IP Helper Addressing" section, the documentation explains the need for helper addresses. It states, "When a router receives a broadcast packet, the packet is not forwarded." This confirms that the default action is to not forward (i.e., drop) broadcasts. The existence of the IP helper feature is to selectively override this default behavior for specific UDP broadcasts like DHCP. (Reference Section: "IP Helper Addressing").

2. Stallings, W. (2016). Data and Computer Communications (10th ed.). Pearson. Chapter 18, "Internet Protocol," explains that routers interconnect networks and that a key function is to contain broadcasts. The text clarifies that routers do not forward limited or directed broadcast datagrams by default, effectively dropping them at the network boundary. (Reference Section: Chapter 18.2, "IP Addresses"). This is a standard textbook used in university computer science and engineering curricula.