CCNA ITN: Module 9

MAC address

physical address unique to each network interface

IP address

logical address used to identify devices on a network

same network

destination MAC is that of the destination device

remote network

destination MAC is that of the default gateway

IPv4 address resolution

uses Address Resolution Protocol (ARP)

IPv6 address resolution

uses ICMPv6 Neighbor Discovery Protocol

ARP

purpose is to map IPv4 addresses to MAC addresses

ARP cache

temporarily stores IP-to-MAC mappings in RAM

ARP request

broadcast frame asking for MAC address of specific IPv4

ARP reply

unicast response containing requested MAC address

ARP frame type

hexadecimal value 0x806 in Ethernet frame

ARP request encapsulation

sent directly in Layer 2 Ethernet frame

ARP table

entry removed after timeout or manually cleared

static ARP entries

manually entered, rarely used

ARP performance drop

happens when many devices boot and flood network

ARP spoofing

threat actor sends fake ARP reply to redirect traffic

Windows ARP table command

arp -a

Cisco ARP table command

show ip arp

ICMPv6 Neighbor Discovery

replaces ARP in IPv6

ND message types

Neighbor Solicitation, Neighbor Advertisement, Router Solicitation, Router Advertisement, Redirect

Neighbor Solicitation

ICMPv6 message used to find MAC for a given IPv6 address

Neighbor Advertisement

ICMPv6 message replying with MAC address

Router Solicitation

host message asking routers to identify themselves

Router Advertisement

router response with address info, prefixes, etc.

Redirect message

informs host of better first-hop router

IPv6 neighbor messages

use Ethernet and IPv6 multicast addressing

multicast advantage

Ethernet NICs can filter before OS processing

SLAAC

Stateless Address Autoconfiguration via Router Advertisements