Which detail is included in a routing table?

A routing table is a data file in a router that lists the routes to particular network destinations. Its primary purpose is to help the router make forwarding decisions. For any given destination IP address, the router performs a lookup in its routing table to find the best match. The corresponding entry provides the essential information on how to forward the packet, which is either the IP address of the next-hop router or the specific outgoing interface on the local router that leads toward the destination.

A. IP protocol: The IP protocol field (e.g., TCP, UDP, ICMP) is Layer 3 information but is not a column in a standard routing table used for destination-based forwarding.
B. Broadcast address: A broadcast address is a type of destination address, not a component or field within a routing table entry that defines a path.
C. TCP or UDP port number: This is Layer 4 information. Standard routing decisions are made at Layer 3 using the destination IP address, not Layer 4 port numbers.

1. Cisco Systems, Inc., IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Gibraltar 16.12.x, "Information in the IP Routing Table". This official documentation details the components of a routing table entry, explicitly listing the destination network and mask, and "the address of the next-hop router or the outgoing interface."

2. Peterson, L., & Davie, B. S. (2011). Computer Networks: A Systems Approach (5th ed.). Morgan Kaufmann. Chapter 3, "Internetworking," Section 3.2.3, "Forwarding," describes the forwarding table (or routing table) as containing entries of the form (Prefix, NextHop).

3. Almquist, P. (June 1995). RFC 1812: Requirements for IP Version 4 Routers. Internet Engineering Task Force (IETF). Section 5.2.4, "The Forwarding Table," specifies that the forwarding database must contain the destination address, next-hop router, and next-hop network interface for each route.