Network Services

Question 1

What are the 4 steps of DHCP assignment.

Answer 1

1. Discover
2. Offer
3. Request
4. Acknowledgement

Question 2

What are the 4 settings assigned by DHCP?

Answer 2

• IP Address
• Subnet Mask
• Default Gateway
• DNS/WINS Server

Question 3

When do we need an IP Helper address?

Answer 3

When the DHCP Server and Client are on different network segments, the router on the Clients segment, needs to be configured with an IP Helper address in order to be able to forward the requests to the DHCP server. This IP address mostly is the IP of a DHCP relay.

Question 4

What is an IP Helper?

Answer 4

It forwards several kinds of UDP broadcasts across the router and can be used with a DHCP relay.

Question 5

What is a DHCP relay?

Answer 5

It forwards DHCP packets between clients and servers if clients and servers are on different network segments.

Question 6

What are the 5 levels of DNS?

Answer 6

1. Root Level
2. Top-Level-Domain (.com/.org/.de/.uk etc.)
3. Second-Level-Domain (diontraining, microsoft etc.)
4. Subdomain (www/mail/support/forum etc)
5. Host (Refers to a specific machine)

Question 7

What is a URL?

Answer 7

A Uniform Ressource Locator is the full string to access a webserver, like: https://www.diontraining.com

Question 8

What are the different types (8) of DNS records?

Answer 8

• A: Domain —> IPv4
• AAAA: Domain —> IPv6
• CNAME (Canocial Name): Domain/Subdomain —> Domain/Subdomain
• MX (Mail Exchange): Directs emails to mail server (cant point to IPs)
• SOA (Start of Authority): Stores critical info about domain or zone, needed in zone transfers, that use TCP
• PTR (Pointer): Opposite of A records, used for Reverse DNS Lookups, PTR records always use .arpa top level domain, ex: IP.in-addr.arpa
• TXT: Used for ownership verification
• NS (Nameserver): Indicates which nameserver has the authority over that domain

Question 9

What are internal/external DNS?

Answer 9

Internal DNS: Allows cloud instances on the same network to access each other using internal DNS names with internal A and PTR records.

External DNS: Thats the DNS we all know, that is used to reach domains over the internet.

Question 10

Whats the TTL?

Answer 10

The Time To Live is used to tell a DNS resolver how long a cached record is valid until it has to request a new record from the server.

Question 11

What are the two types of DNS Lookups if a DNS server doesnt know a requested IP address?

Answer 11

Recursive Lookup: The DNS Server goes up the levels until it finds the requested IP address.

Iterative Lookup: The DNS resolver keeps asking other DNS Servers until one of the either knows the IP or knows a DNS server that knows the IP

Question 12

What are 3 ways to secure DNS against eavesdropping and DNS Snooping?

Answer 12

DNS over HTTPS (DoH): Sends all DNS queries through https like most webtraffic is nowadays

DNS of TLS (DoT): Sends all DNS queries through an encrypted transport layer security tunnel, pretty much like DoH but using TLS instead of SSL.

DNS Security Extension (DNSSEC): Provides authentication and integrity checking for DNS data, preventing DNS spoofing and poisoning.

Question 13

What is NTP and what port is it running on?

Answer 13

Network Time Protocol (NTP): Is used to synchronize computer clocks over the network in a very accurate way, it does that on Port 123.

Question 14

What are newer alternatives to NTP?

Answer 14

Precision Time Protocol (PTP): More precise, sub-microsecond, for networks that need really accurate clocks

Network Time Security (NTS): Extension for NTP that provides cryptographic security for the time synching. Uses TLS and AEAD

Question 15

What is QoS and what are the 3 metrics used to measure it?

Answer 15

Quality of Service (QoS) is the principle of categorizing your network traffic and prioritizing the different categories based on the needs of the company. Delay when sending an email is for example way more acceptable than Delay of packets in a VoiP call.
The 3 metrics are:
- Delay
- Jitter (Jumbling of signals)
- (Packet) Drops

Question 16

What are the 3 types of QoS ruling?

Answer 16

1. Best Effort: no categories, no priorities / No QoS
2. Integrated Services (IntServ): Traffic types have strict bandwith reservations / Hard QoS
3. Differentiated Services (DiffServ): Diffenrentiation of data types where routers and switches can shift bandwith based on whats available / Soft QoS