Podcast
Questions and Answers
What is the primary function of the Address Resolution Protocol (ARP)?
What is the primary function of the Address Resolution Protocol (ARP)?
What happens when an ARP table entry times out?
What happens when an ARP table entry times out?
In which scenario would a default gateway's MAC address need to be resolved using ARP?
In which scenario would a default gateway's MAC address need to be resolved using ARP?
What is one of the key differences between ARP for IPv4 and Neighbor Discovery (ND) for IPv6?
What is one of the key differences between ARP for IPv4 and Neighbor Discovery (ND) for IPv6?
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What command would you use on a Cisco Router to view the ARP table?
What command would you use on a Cisco Router to view the ARP table?
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Which mechanism can a malicious host use to exploit ARP?
Which mechanism can a malicious host use to exploit ARP?
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What is the purpose of Neighbor Solicitation messages in IPv6 Neighbor Discovery?
What is the purpose of Neighbor Solicitation messages in IPv6 Neighbor Discovery?
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What type of ARP message is sent when a device needs to find out the MAC address for an IP address not in its ARP table?
What type of ARP message is sent when a device needs to find out the MAC address for an IP address not in its ARP table?
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Study Notes
Address Resolution Protocols
- Devices on Ethernet LANs need both logical (IP) and physical (MAC) addresses.
- To transmit data, a host requires the destination MAC address.
IPv4 Address Resolution Protocol (ARP)
- ARP maps IPv4 addresses to MAC addresses on a local network.
- ARP maintains a temporary ARP table (cache).
- ARP Request: A broadcast message ("Who has IP x.x.x.x? Tell me your MAC!") sent if the MAC is not in the ARP table.
- Destination MAC = FF:FF:FF:FF:FF:FF (all devices on the local LAN).
- ARP Reply: A unicast response from the device with the matching IPv4 address ("My MAC is XX:XX:XX:XX:XX:XX").
- Sender updates its ARP table with the new information.
- To send to a remote IPv4 network, the destination MAC is the default gateway's MAC.
- ARP table entries timeout (e.g., 15-45 seconds on Windows).
IPv6 Neighbor Discovery (ND)
- IPv6 uses ICMPv6 for address resolution and other tasks.
- Neighbor Solicitation: "Who has IPv6 address X?" (using multicast addresses).
- Neighbor Advertisement: "I have IPv6 address X; MAC is Y."
- ND is analogous to ARP, but uses ICMPv6 and multicast.
Data Flow Summarization (IPv4)
- Local IPv4: Check ARP table for destination IP's MAC; if not found, send a broadcast ARP request, receive a reply, update ARP cache, and send the frame.
- Remote IPv4: Destination is off-network; uses default gateway's MAC (obtained via ARP if needed) and sends frames to the router.
Data Flow Summarization (IPv6)
- Local/remote IPv6: Check Neighbor Cache for destination or gateway's MAC; if not found, send an ICMPv6 Neighbor Solicitation to a special multicast address, receive a reply, and update the neighbor cache, sending the frames.
ARP and ND Differences
- ARP uses broadcasts; ND uses special multicast addresses (with ICMPv6).
- This difference in addressing is key when troubleshooting or configuring IPv4 vs. IPv6 networks.
ARP Table Maintenance
- Entries time out to prevent stale data.
- Command examples (Windows & Cisco Router):
- Windows:
arp -a - Cisco Router:
show ip arp
- Windows:
ARP Issues
- Excessive ARP broadcasts can overwhelm the network and cause brief congestion.
- Spoofing (ARP poisoning) allows malicious hosts to intercept data.
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Description
This quiz covers the fundamentals of Address Resolution Protocols, including ARP for IPv4 and Neighbor Discovery for IPv6. It explains how devices on Ethernet LANs map logical IP addresses to physical MAC addresses and the processes involved in ARP requests and replies. Test your understanding of these protocols and their role in network communication.
