Networks Training

  • About
  • My Books
  • SUGGESTED TRAINING
  • HOME
  • Cisco Networking
    • Cisco General
    • Cisco IOS
    • Cisco VPN
    • Cisco Wireless
  • Cisco ASA
    • Cisco ASA General
    • Cisco ASA Firewall Configuration
  • Certifications Training
    • CCNA Training
    • Cisco Certifications
    • I.T Training
  • General
    • General Networking
    • IP Telephony
    • Network Security
    • Product Reviews
    • Software
  • Cisco Routers
  • Cisco Switches
You are here: Home / CCNA Training / What is Address Resolution Protocol-ARP

What is Address Resolution Protocol-ARP

Written By Harris Andrea

ARP (Address Resolution Protocol) is a Layer2 protocol that is used to translate IP addresses (layer 3 in OSI model ) to MAC addresses (layer 2 in OSI model ), and is used when two hosts on a Local Area Ethernet Network want to communicate with each other.

Of course ARP is used in other Layer 2 networks such as ATM for example, but the main usage of ARP is on Ethernet Networks.

The first time Host A wants to contact Host B, Host A sends an ARP Request (using a broadcast packet) on the LAN. The ARP packet basically asks the following “I have the IP address for Host B and I want to know the MAC address of Host B”.

Host B sees this broadcast packet and replies to Host A with an ARP Reply packet containing host B’s MAC address.

Host A now saves this MAC address/IP address combination in its ARP cache and begins to communicate with host B.

This communication happens with Layer2 MAC Addresses because the two hosts are on the same Layer 2 network.

MORE READING:  Cisco Access List Configuration Examples (Standard, Extended ACL) on Routers Etc

To display the contents of a host’s ARP cache (table), use “arp-a” on a Windows platform, “arp” on a UNIX platform, and “show arp” on a Cisco IOS platform.

Now, what if the destination host is not on the same Layer 3 subnet of the origin host? In this case, the default gateway router of the origin host will reply to the ARP request and give its own MAC address so the origin host will send its packets to the default gateway in order to reach the destination host.

The default gateway will take the packets and using Layer 3 routing will send the packets to the correct interface in order to reach the destination host (of course the packets can traverse several routers before reaching the final destination).

Related Posts

  • Cisco Access List Configuration Examples (Standard, Extended ACL) on Routers Etc
  • 10 Best Network Engineer Certifications to Pursue for Your Career
  • 6 Practice Lab Options for CCNA CCNP CCIE
  • What is Unicast, Broadcast and Multicast
  • Some Questions and Answers about the Cisco CCNA Exam

Filed Under: CCNA Training

Download Free Cisco Commands Cheat Sheets

Enter your Email below to Download our Free Cisco Commands Cheat Sheets for Routers, Switches and ASA Firewalls.

We use Elastic Email as our marketing automation service. By submitting this form, you agree that the information you provide will be transferred to Elastic Email for processing in accordance with their Terms of Use and Privacy Policy. Also, you allow me to send you informational and marketing emails from time-to-time.

About Harris Andrea

Harris Andrea is an Engineer with more than two decades of professional experience in the fields of TCP/IP Networks, Information Security and I.T. Over the years he has acquired several professional certifications such as CCNA, CCNP, CEH, ECSA etc.

He is a self-published author of two books ("Cisco ASA Firewall Fundamentals" and "Cisco VPN Configuration Guide") which are available at Amazon and on this website as well.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Search this site

About Networks Training

We Provide Technical Tutorials and Configuration Examples about TCP/IP Networks with focus on Cisco Products and Technologies. This blog entails my own thoughts and ideas, which may not represent the thoughts of Cisco Systems Inc. This blog is NOT affiliated or endorsed by Cisco Systems Inc. All product names, logos and artwork are copyrights/trademarks of their respective owners.

Amazon Disclosure

As an Amazon Associate I earn from qualifying purchases.
Amazon and the Amazon logo are trademarks of Amazon.com, Inc. or its affiliates.

Search

BLOGROLL

Tech21Century
Firewall.cx

Copyright © 2023 | Privacy Policy | Terms and Conditions | Hire Me | Contact | Amazon Disclaimer | Delivery Policy

0 shares