CCNA 1 Module 9: Address Resolution PDF

Destination on Same Network There are two primary addresses assigned to a device on an Ethernet LAN: Layer 2 physical address (the MAC address) – Used for NIC to NIC communications on the same Ethernet network. Layer 3 logical address (the IP address) – Used to send the pa...

Destination on Same Network There are two primary addresses assigned to a device on an Ethernet LAN: Layer 2 physical address (the MAC address) – Used for NIC to NIC communications on the same Ethernet network. Layer 3 logical address (the IP address) – Used to send the packet from the source device to the destination device. Layer 2 addresses are used to deliver frames from one NIC to another NIC on the same network. If a destination IP address is on the same network, the destination MAC address will be that of the destination device. Network Interface Controller (NIC) Media Access Control (MAC) Internet Protocol (IP) Internet Control Message Protocol (ICMP) © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 1 Destination on Remote Network When the destination IP address is on a remote network, the destination MAC address is that of the default gateway. How to get the MAC address that is associated with a known IP address: ARP (Address Resolution Protocol) is used by IPv4 to associate the IPv4 address of a device with the MAC address of the device NIC in the local network. ICMPv6 is used by IPv6 to associate the IPv6 address of a device with the MAC address of the device NIC in the local network. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2 ARP Overview and functions A device uses ARP to determine the destination MAC address of a local device when it knows its IPv4 address. ARP provides two basic functions: Resolving IPv4 addresses to MAC addresses Maintaining an ARP table of IPv4 to MAC address mappings. To send a frame, a device will search its ARP table for a destination IPv4 address and a corresponding MAC address. If the packet’s destination IPv4 address is on the same network, the device will search the ARP table for the destination MAC address. If the destination IPv4 address is on a different network, the device will search the ARP table for the MAC address of the default gateway. If the device locates the IPv4 address, its corresponding MAC address is used as the destination MAC address in the frame. If there is no ARP table entry is found, then the device sends an ARP request. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3 IPv6 Neighbor Discovery Messages IPv6 Neighbor Discovery (ND) protocol provides: Address resolution Router discovery Redirection services ICMPv6 Neighbor Solicitation ‫تحريض‬/‫( حث‬NS) and Neighbor Advertisement (NA) messages are used for device-to-device messaging such as address resolution. ICMPv6 Router Solicitation (RS) and Router Advertisement (RA) messages are used for messaging between devices and routers for router discovery. ICMPv6 redirect messages are used by routers for better next-hop selection. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 4 IPv6 Neighbor Discovery – Address Resolution IPv6 devices use ND to resolve the MAC address of a known IPv6 address. ICMPv6 Neighbor Solicitation messages are sent using special Ethernet and IPv6 multicast addresses. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 5