1.6 Network Services

Question 1

DNS
A and AAAA record

Answer 1

A - FQDN to ipv4
AAAA - FQDN to IPv6

Question 2

Dns
CNAME record

Answer 2

Domain name to alias

Question 3

Dns
Mx record

Answer 3

Mail exchange

Question 4

Dns
SOA record

Answer 4

Start of authority
-describes dns zone details

Question 5

Dns
Ptr record

Answer 5

Provides domain name associated with IP address (reverse dns lookups)

IPv4:
Stored under IP address reversed with “.in-addr.arpa” at the end
(For example, the PTR record for the IP address 192.0.2.255 would be stored under “255.2.0.192.in-addr.arpa”.)

IPv6:

IPv6 PTR records are stored under the IPv6 address, reversed and converted into four-bit sections (as opposed to 8-bit sections, as in IPv4), plus “.ip6.arpa”.

The PTR record in IPv6 for the IP address 4321:0:1:2:3:4:567:89ab would be stored under “b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.IP6.ARPA”.

arpa is the top level domain name defined for the internet

common uses for PTR records are anti-spam, troubleshooting email delivery issues, and logging

Question 6

Dns
Txt record

Answer 6

A TXT record is a DNS record that provides text information to sources outside your domain, that can be used for a number of arbitrary purposes. The record’s value can be either human- or machine-readable text. With Google Cloud services, TXT records are used to verify domain ownership and to implement email security measures such as SPF, DKIM, and DMARC.

Question 7

Dns
SRV record

Answer 7

The DNS “service” (SRV) record specifies a host and port for specific services such as voice over IP (VoIP), instant messaging, and so on. Most other DNS records only specify a server or an IP address, but SRV records include a port at that IP address as well. Some Internet protocols require the use of SRV records in order to function.

_service._proto.name. TTL class type of record priority weight port target.

_xmpp._tcp.example.com. 86400 IN SRV 10 5 5223 server.example.com.

Question 8

Dns
NS record

Answer 8

NS stands for ‘nameserver,’ and the nameserver record indicates which DNS server is authoritative for that domain (i.e. which server contains the actual DNS records). Basically, NS records tell the Internet where to go to find out a domain’s IP address. A domain often has multiple NS records which can indicate primary and secondary nameservers for that domain. Without properly configured NS records, users will be unable to load a website or application.

domain.com. 21600 IN NS emely.ns.cloudflare.com

In this example, the domain domain.com lies within the zone of the authority of the name servers named emely

Question 9

Dns
Zone transfers

Answer 9

Processing of copying the contents of the zone file on a primary server to secondary dns server

Question 10

Dns
Global hierarchy

Answer 10

Root
Top level domains (.net, .com, .gov)
Secondary (example.com)
Subdomain (www.example.com)
Host (node.cluster.example.com)

Question 11

Dns
Reverse dns lookup

Answer 11

Ip to FQDN

Question 12

Dns recursive lookup

Answer 12

Delegate the lookup to a dns server
Dns server does the work to find the ip and reports back

Question 13

Dns iterative lookup

Answer 13

Your host does all the queries itself

Question 14

Dns
Authoritative name servers

Question 15

DHCP
Relay

Answer 15

Provides a way for dhcp clients to communicate with server on another subnet.
Relay agent uses ip routing to forward discover messages to a server and relays the offer back to the client network.

Question 16

DHCP
Ip helper/UDP forwarding

Answer 16

Command to enable dhcp relay in a router.

Question 17

Dhcp
Lease time

Question 18

NTP
Stratum

Question 19

NTP
Clients

Question 20

NTP
Servers

Question 21

DNS email security in TXT records (SPF/DKIM/DMARC)

Answer 21

Sender Policy Framework (SPF): Specifies the servers and domains that are authorized to send email on behalf of your organization.

DomainKeys Identified Mail (DKIM): Adds a digital signature to every outgoing message, which lets receiving servers verify the message actually came from your organization.

Domain-based Message Authentication, Reporting, and Conformance (DMARC): Lets you tell receiving servers what to do with outgoing messages from your organization that don’t pass SPF or DKIM

Question 22

Split-view DNS

Answer 22

Separate DNS servers are provided for security and privacy management for internal and external networks.

-using logical and physical separation of dns for network-internal access and access from public internet
-2 sets of DNS that are given based on source address or the requestor.