1 day

PDU

layer 4 - segment

layer 3 - packet

layer 2 - Frame

OSI Model

• physical

• data link

• network

• transport

• session

• presentation

• application

TCP/IP stack

• link

• internet

• transport

• application

Private IP range

• 10.0.0.0 → 10.255.255.255

• 172.16.0.0/12 → 172.31.255.255

• 192.168.0.0 → 192.168.255.255

RFC 1918

private ip addresses

ipv4 vs ipv6 bit size

32 → 128

FQDN

Fully qualified domain name www.cisco.com

If the internal DNS server can’t resolve

then it uses UDP53 to send to public DNS server

Find your default gateway, DNS server, ip address

cmd → ipconfig /all

find the hostname + ip address of DNS

nslookup google.com

Configure what DNS server to use on a router

→ ip domain-lookup

→ ip name-server 172.23.4.1

→ip domain-list ###.com

View interfaces → ip address + status

show ip int br

Configure R1 to use r3 (10.10.20.1) as it’s DNS server

• ip domain-lookup

• ip name-server 10.10.20.1

• ip domain-list ###.com

ARP

address resolution protocol → it bridges layer 2 and 3 by resolving IP address to Mac address

ARP purpose

Maps an IPv4 address to a physical MAC address to enable local network communication.

ARP request

broadcast ffff.ffff.ffff

ARP reply is

unicast

View ARP cache on windows

arp -a

DHCP uses

UDP 67 → DORA

For ARP requests on a different subnet/network

it sends arp request to it’s default gateway

View ARP on a Router

show arp

Clear Arp on Cisco Router

clear arp-cache