Domain 1.6

Question 1

Describe the four step DHCP process

Answer 1

DORA -

Discover - The client sends DHCP discover message to broadcast.

Offer - DHCP client responds to the request with a currently available DHCP configuration

Request - The client formally requests the information sent to it by the DHCP server.

Acknowledge - The DHCP server sends an acknowledgement to the requestor.

Question 2

True or False: DHCP requests will be answered if there is no DHCP server on the subnet

Answer 2

False:

DHCP requests use the broadcast address to contact the DHCP server. If there is no server on the subnet, there will be no IP assignment.

Question 3

How do DHCP Servers respond to Discover requests that are not on the same subnet.

Answer 3

A DHCP relay can be configured on the router of the subnet.
The relay will forward the discover request to a different subnet with the router as the source address. When the DHCP server responds to the router, beginning the DORA process, the router sends the information back to the original requestor on its subnet.

Question 4

What are the properties that are configured in a DHCP scope

Answer 4

IP Address range
IP Address Exclusions

Subnet Mask
Lease duration
DNS server
Gateway information.

Question 5

What is a DHCP pool

Answer 5

Grouping of IP addresses

Each subnet will have its won scope and scope options.

Scope will normally be a contiguous pool of IP addresses

Question 6

What are the three DHCP assignment methods

Answer 6

Dynamic

Automatic

Static

Question 7

Describe the Dynamic DHCP Address Assignment method

Answer 7

DHCP Server has a large pool of addresses.

Addresses are leased to and returned by the host following the four step process (DORA)

Question 8

Describe the Automatic DHCP Address Assignment method

Answer 8

Similar to Dynamic, DHCP server keeps list of past assignments, and provides the same IP address to hosts every time

Question 9

Describe the Static DHCP Address Assignment method

Answer 9

Administratively configured table of MAC addresses. Each MAC address has its own IP Address.

AKA “IP Reservation, Static Assignment”

Question 10

What is a T1 Timer?

Answer 10

A timer that once a DHCP lease reaches 50% of its lease, will cause the client to check in with the lending DHCP server to renew its lease.

Question 11

What is a T2 Timer

Answer 11

A timer that is activated once a DHCP lease has passed %87.5 (7/8ths) of the lease duration.

If the lending DHCP server is not available, it will try to rebind its IP address with any server.

Question 12

compare Internal and External DNS

Answer 12

Internal DNS -
Managed by internal team
Holds DNS information about internal devices

External DNS -
Often managed by third party
Does not have internal device infomration

Question 13

What are the type of DNS lookups

Answer 13

Forward lookups - The DNS server is provided with an FQDN, the DNS server then responds with an IP address

Reverse Lookups - Provides the DNS server with an IP Address. The DNS server then replies with an FQDN

Question 14

what is a recursive DNS Query

Answer 14

A resolver contacts a DNS server that then performs lookup actions if the DNS server does not have the response cached.

The DNS server does the work and reports back.

Large DNS cache can provide a speed advantage

Question 15

What is an Iterative DNS query

Answer 15

The DNS resolver performs all of the work resolving DNS to IP itself.

The DNS cache is specific to the host that is performing the lookups.

Question 16

What are the different DNS record types

Answer 16

Resource Records (RR)
Start of Authority (SOA)
Address records (A) (AAAA)
Canonical Names (CNAME)
Service Records (SRV)
Mail Exchanger (MX)
Name Server Records (NS)
Pointer Records (PTR)
Text Records (TXT)

Question 17

What is a resource record

Answer 17

The database records of domain name services

Over 30 types IP address, Certificates, host alias names

Question 18

Describe an SOA

Answer 18

Start of Authority -

Record that describes the DNS Zone Details

Structure -
IN SOA (Domain Name)
-Serial Number
- Refresh, Retry Time Frames
-Caching Duration/TTL

Question 19

Describe both A and AAAA records

Answer 19

Address records
A = IPv4
AAAA - IPV6

Defines the IP address of a host
- Most popular query

Question 20

Describe a CNAME Record

Answer 20

A name is an alias of another canonical name

Used when you have a single physical server that has multiple services running on it.

Question 21

Describe a Service Record

Answer 21

Record that finds a specific service offered on a server.

Question 22

Describe an MX record

Answer 22

Mail Exchanger Record -

Determines the host name for the mail server

Not an IP address, just a name

Question 23

Describe an NS record

Answer 23

Name Server Record -
list the name servers for a domain, NS records point to the name of the server.

Question 24

Describe a PTR record

Answer 24

The reverse of a A or AAAA record.
Added to a reverse map zone file.

Question 25

Describe a TXT record

Answer 25

Human readable text information that can be used for showing public information.

SPF and DKIM information can be stored in a PTR record.

Question 26

What is SPF

Answer 26

Sender policy framework is a protocol that can be used to prevent mail spoofing from a domain.

Mail servers verify that incoming mail came from an authorized host.

Question 27

What is DKIM

Answer 27

Domain Keys Identified Mail -

Allows for digitally signing your outgoing mail.

Validated by the mail server,. not usually seen by the end user.

Put your public key in the DKIM TXT record so mail signed with private key can be validated.

Question 28

Describe a zone transfer

Answer 28

The replication of a DNS database.

A primary DNS server has the primary copy of the zone information.

This allows for redundancy as secondary DNS servers can pull records.

Zone transfers are triggered by referencing the serial number. if the serial number increases, there must have been a change.

Full zone transfers can be a security risk.

Question 29

What port does NTP run on

Answer 29

UDP/123

Question 30

What are the different NTP toplogies

Answer 30

NTP Server
NTP Client
NTP Client/Server

Question 31

Describe NTP Clients and Servers

Answer 31

NTP Clients - requests time updates form a server,

NTP Servers - Respond to time requests from NTP Clients.
NTP Servers also do not control or adjust their own time

Question 32

What does an NTP Client/Server do

Answer 32

Requests time updates from NTP servers.

Responds to time requests from other NTP clients

Question 33

What is a Stratum

Answer 33

A number assocaited with the distance a NTP client is from the original NTP reference clock.

Question 34

What is Stratum 0 mean

Answer 34

A very reliable NTP clock.

Atomic, or GPS clock

Question 35

What is Stratum 1 Mean

Answer 35

A clock that is syncd with a Stratum 0 clock. Used for a primary time server

Question 36

What is a Stratum 2

Answer 36

A clock that is synched with a Stratum 1 server