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200-301 · Question #708

When troubleshooting ethernet connectivity issues how can you verify that an ip address is known to a router?

The correct answer is D. Check Whether the ip address is in the ARP Table. To verify that a router knows the MAC address corresponding to an IP address on a directly connected Ethernet segment, you should check its ARP table. The ARP table maps IP addresses to MAC addresses, which is essential for Ethernet frame encapsulation and local delivery.

Submitted by hassan_iq· Mar 5, 2026IP Connectivity

Question

When troubleshooting ethernet connectivity issues how can you verify that an ip address is known to a router?

Options

  • ACheck Whether the ip address is in the routing table
  • BCheck Whether an ACL is blocking the ip address
  • CCheck Whether the ip address is in the CAM Table
  • DCheck Whether the ip address is in the ARP Table

How the community answered

(37 responses)
  • A
    3% (1)
  • B
    8% (3)
  • C
    11% (4)
  • D
    78% (29)

Why each option

To verify that a router knows the MAC address corresponding to an IP address on a directly connected Ethernet segment, you should check its ARP table. The ARP table maps IP addresses to MAC addresses, which is essential for Ethernet frame encapsulation and local delivery.

ACheck Whether the ip address is in the routing table

The routing table indicates how to reach network prefixes (subnets), not specific host IP addresses directly within a segment, and it contains next-hop IP addresses or interfaces, not MAC addresses.

BCheck Whether an ACL is blocking the ip address

An ACL (Access Control List) filters traffic based on various criteria but does not directly indicate if an IP address itself is 'known' or resolved by the router.

CCheck Whether the ip address is in the CAM Table

The CAM (Content Addressable Memory) table is typically found on switches and maps MAC addresses to physical ports, primarily for Layer 2 forwarding decisions, not for IP-to-MAC resolution on a router.

DCheck Whether the ip address is in the ARP TableCorrect

The ARP (Address Resolution Protocol) table on a router maps IP addresses to MAC addresses for devices on directly connected Ethernet segments. If an IP address is known and reachable on the local segment, its MAC address will be present in the router's ARP table.

Concept tested: ARP table for local IP resolution

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_arp/configuration/15-mt/arp-15-mt-book/arp-config-arp.html

Topics

#ARP Table#IP-to-MAC resolution#Ethernet troubleshooting#Router ARP

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