TCP\IP Basics

Question 1

Where does Internet Protocol work?

TCIP Model

Answer 1

• at the internet layer
• takes data chunks from the transport layer
• adds addressing
• creates final IP Packet

Question 2

Protocols of the internet layer?

Answer 2

• IPv4
• IPv6
• ICMP

Question 3

parts of an IP Packet?

Answer 3

• version - 4 or 6
• header length - total size of ip portion of packet
• DSCP - differentiated services code point - contains data used by bandwidth-sensative applications like voice over ip
• TTL - prevents loops by using a counter
• protocol - TCP or UDP

Question 4

TCP connection rules

Answer 4

• uses 3 way handshake
• SYN, SYN-ACK, ACK
• gives all segments a sequence number to verify all segments received
• if segment missing, the receiving system must request

Question 5

parts of a tcp header

Answer 5

• source port
• destination port
• sequence number
• ack
• flags - state of connection
• checksum - checks header for errors

Question 6

protocol for DNS and DHCP

Answer 6

UDP

Question 7

how does the packet find the reciving computers MAC address?

Answer 7

sends out an ARP (address resolution protocol) request to MAC address FF-FF-FF-FF-FF-FF

Question 8

view arp cache in windows CLI

Answer 8

arp -a

Question 9

Three things the IP numbering system must do:

Answer 9

1) create network IDs
2) Interconnect LANs using routers / give routers a way to use the network ID to send packets
3) use subnet mask to recognize if the packet is for the LAN or WAN

Question 10

WAN

Answer 10

Wide Area Network

- a group of two or more interconnected LANs

Question 11

Network ID

Answer 11

unique identifier for a LAN

Question 12

Host ID

Answer 12

part of the IP that isn’t the Network ID

cannot end in 0

Question 13

Routing table

Answer 13

instructions built into a router that instructs it what to do with incoming packets and where to send them

Question 14

subnet mask

Answer 14

• a bunch of 1’s followed by some number of zero’s
• always totals 32 bits
• 1’s always line up with network id in ip address
• 0’s always line up with host id in ip address

Question 15

what happens when a computer wants to send to an IP address

Answer 15

• it will send to default gateway

- still does arp request to get MAC address for gateway

Question 16

what is a whack

Answer 16

a slash followed by the number of ones in the subnet mask

• /24 = 24 ones - 255.255.255.0
• /16 = 16 ones - 255.255.0.0
• /8 = 8 ones - 255.0.0.0

Question 17

a computer needs what to work in a network environment

Answer 17

• ip address that’s part of it’s network ID
• subnet mask
• default gateway

Question 18

what organization tracks and disperses ip addresses globally

Answer 18

IANA

• Internet Assigned Numbers Authority
• hands out IPs in contiguous chunks called network blocks

Question 19

what organization tracks and disperses ip addresses regionally

Answer 19

RIR

• Regional Internet Registries
• there are 5

Question 20

What is the RIR for north america?

Answer 20

ARIN

American Registry for Internet Numbers

Question 21

class A network block

Answer 21

first decimal 1-126
1.0.0.0 - 126.255.255.255
16M hosts per network ID

Question 22

class B network block

Answer 22

first decimal 128-191
128.0.0.0 - 191.255.255.255
65K hosts per network ID

Question 23

class C network block

Answer 23

first decimal 192-223
192.0.0.0 - 223.255.255.255
254 hosts per network id

Question 24

class d network block

Answer 24

first decimal 224-239
224.0.0.0 - 239.255.255.255
multicast

Question 25

class e network block

Answer 25

first decimal 240-254 240.0.0.0 - 254.255.255.255 experimental

Question 26

multicast class blocks

Answer 26

- used for one-to-many communication - can send packet with a broadcast, unicast, or multicast - multicast often used when routers talk to each other

Question 27

CIDR

Answer 27

- Classless Inter-Domain Routing | - ISP is given a block of addresses, subnets block into multiple subnets, then passes out smaller subnets to customers

Question 28

VLSM

Answer 28

Variable Length Subnet Masking

Question 29

BOOTP

Answer 29

bootstrap protocol | - predates DHCP, does same thing

Question 30

how dhcp works

Answer 30

Four way handshake or DORA (Discover, offer, request, acknowledgement) - client sends DHCP Discover message using broadcast when it boots up - server sends DHCP offer message (includes IP address, subnet mask and gateway) - client sends DHCP request (accepting offer) - server sends DHCP Acknowledgement (unicast) - client receives DHCP lease (good for fixed amount of time, usually 1 to 8 days) - near end of lease, client sends out another DHCP request

Question 31

DHCP ports

Answer 31

UDP 67 (server) and 68 (client)

Question 32

What does a DHCP server need?

Answer 32

- pool of ip addresses to pass out - know subnet mask of network - ip address of default gateway

Question 33

DHCP scope

Answer 33

range of ip address for server to hand out

Question 34

DHCP scope options

Answer 34

choices like default gateway, dns server, network time server, etc

Question 35

DHCP relay

Answer 35

- built into most routers - accepts DHCP broadcasts from clients then sends them via unicast directly to the DHCP server by IP address (IP helper address)

Question 36

DHCP TTL

Answer 36

Time to Live | - determines how many routers (hops) a DHCP relay can be from the helper IP

Question 37

IP Exclusion in DHCP

Answer 37

an address that the dhcp server will not hand out (for clients with static ip)

Question 38

MAC Reservation in DHCP

Answer 38

assigns ip by MAC address

Question 39

ip address when DHCP cant be reached

Answer 39

169. 254.*.* - generated by zeroconf (zero-configuration networking) - Microsofts APIPA (Automatic Private IP Addressing) - can not issue default gateway

Question 40

Renew lease windows CLI

Answer 40

ipconfig /release | ipconfig /renew

Question 41

Renew lease Mac CLI

Answer 41

sudo ifconfig eth0 down | sudo ifconfig eth0 up

Question 42

Renew lease linux CLI

Answer 42

sudo dhclient -r | sudo dhclient

Question 43

DHCP Failover

Answer 43

2 (only 2) dhcp servers work together to provide DHCP for the network (primary and secondary) - share a single scope - if either fails, the other picks up

Question 44

rogue DHCP

Answer 44

another DHCP server added to the network handing out wrong addresses

Question 45

private ip addresses

Answer 45

10. 0.0.0 - 10.255.255.255 (1 class a network block) 172. 16.0.0 - 172.31.255.255 (16 class b network blocks) 192. 168.0.0 - 192.168.255.255 (256 class c network blocks)