Explaining Network Services

Question 1

DCHP

Answer 1

Dynamic Host Configuration Protocol

• Automatic allocation of an IP adress, subnet mask and additional parameters, like default gateway or DNS server
• Host is configured to user DHCP by specifying in TCP/IP configuration that it shoud automatically obtain IP

Question 2

DHCP Server

Answer 2

• Normally deployed as service of network opreating system or through appliance such as a switch or router
• Must be allocated a static IP address and configured with a pool of IPs and a subnet masks

Question 3

Scope

Answer 3

• Range of addresses and options configured to a single subnet
• Must provide start and end IP address and subnet mask
• No scope can cover more than one subnet or vice versa

Question 4

DHCP Lease Time

Answer 4

• Client can renew lease when at least half of the time has elapses (T1 Timer).
• If DHCP server does not respond, client attempts to rebind same lease configuration with any DHCP server, by default at 87.5% of lease time up (T2 timer)
• Long lease time mean less need to renew
• Short least time means IP pool is refilled more ofte.

Question 5

DHCP Options

Answer 5

• Other IP related settings offers in DHCP configuraitons
• Each is identified with tag byte or decimal value between 0-255
• ExampleSS:
  Default gateway
  IP address of DNS server
  DNS suffixx
  Useful server options like NTP, TFTP or VoIP proxy

Question 6

DCHP Reservations

Answer 6

• Mapping of MAC address to specific IP address withing DHCP server address pool
• When server receives request from given interface, it always gives same IP address
• Automatically allocated reserveration refers to address that is permanently leased to a client
• Distinct from Static allocation as the administrator does not determine which specific IP address will be leased

Question 7

DHCP Relay

Answer 7

• Configuration to provide forwarding of DHCP traffic between subnets
• Routers that can do it are RFC 1542 Compliant
• Intercepts DHCP broadcast frames and applies appropriate unicast address for DHCP server
• Reduces the need for multiple DCHP servers for each subnet

Question 8

IP Helper

Answer 8

• Configuration on router to allow set types of brodcast traffic to be forwarded to an interface.
• Supports function of DHCP Relay

Question 9

SLAAC

Answer 9

Stateless Address Autoconfiguration

• IPv6 process that locates routers and generates host address with suitable network prefixx automatically.
• DCHPv6 is often just used for option settings rather than leases for host addresses.

Question 10

Host name

Answer 10

• Assigned to computer by administrator

- Must be unique on local network

Question 11

FQDN

Answer 11

Fully qualified domain name

• Used to provide unique indentity for a host belonging to particular network
• Made up of host name and domain suffix
• Domain name must be registered with registrar to ensure it is unique
• Must follow certain rules:
  1. host name must be unique within domain
  2. Total length cannot exceed 253 characters, with each label(part of name defined by a period) not exceeding 63
  3. Use letter, digit and hyphen characters only.
  4. not case sensitive

Question 12

Iterative Lookups

Answer 12

• Name server responds to query with either requested record or address of name server at a lower level that is authoritative for the namespace
• Makes no effort to make queries for information it does not have.

Question 13

DNS

Answer 13

Domain Name System
- Global hierarchy of distributed names server databases that contain information on domains and hosts withing domains.
- At top is the root, which just contains .
- Next is top level domains(.com,.org,.uk., .gov, etc.)
-

Question 14

Recursive lookup

Answer 14

• if queried server is not authoritative, it does take on take of querying other name servers until it finds requested record or times out.
• Name servers listed in clients TCP/IP configuration accept recursive queries

Question 15

Resource Records

Answer 15

• Record in DNS zone that allows a name server to resolve queries for names and services hosted into IP addresses.
• Can be updated manually (statistically) or can be generated dynamically

Question 16

SOA

Answer 16

State of Authority record

• identifies authoritative name server that maintains complete resource records for the zone
• Also contains contact information for the zone and serial number for version control

Question 17

NS records

Answer 17

Name Server Records

• identify authoritative DNS Name servers for the zone
• Most zones are configured with secondary name servers for redundancy and load balancing

Question 18

A record

Answer 18

Address Record

- Used to resolve a host name to an IPv4 address

Question 19

CNAME Record

Answer 19

Canonical Name Record (or alias)

• Used to configure alias for an existing A record
• Also used to make DNS Administration easier

Question 20

MX Record

Answer 20

Mail Exchange Record

• used to identify email server for the domain
• Host identified must have associated A or AAAA record
• Cannot point to CNAME

Question 21

SRV Records

Answer 21

• Resolves to service name and port on which an application is hosted
• Often used for VoIP and media servers
• Essential part of Active Directory

Question 22

TXT Record

Answer 22

• Used to store any free form text that may be needed to support other network services
• Used as part of SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail)

Question 23

SPF Record

Answer 23

Sender Policy Framework Record

- Used to list the IP addresses or names of servers that are permitted to send from a particular domain

Question 24

DKIM Record

Answer 24

Domain Keys Identified Mail

• Used to decide whether you should allow received mail form given source
• can used encrypted signatures to prove that message originated from where it claims

Question 25

PRT Record

Answer 25

Pointer Record - Reverse DNS lookup zone - Uses a special domain named by the first 3 octets of IP Addresses in the zone in reverse order appended with in-addr.arpa.

Question 26

DHCP Discover

Answer 26

- Type of packet sent by DHCP client a DHCP server | - Sent over UDP with server listening on port 67 and client on port 68

Question 27

DCHPOFFER

Answer 27

- Packet sent by DHCP server as response to DHCPDISCOVER | - Contains IP address and configuration information

Question 28

DCHPREQUEST

Answer 28

- Type of packet sent by client to DHCP server to accept DHCPOFFER

Question 29

DHCPACK Packet

Answer 29

- Packet sent by server to client accepting DHCP

Question 30

DORA

Answer 30

Discover, Offer, Request and Ack(nowlege) | - DHCP Lease process

Question 31

T1 Timer

Answer 31

- Half the time of DHCP Lease | - When a client can renew the lease

Question 32

T2 Timer

Answer 32

- When a client will attemp to rebind same lease configuration with any DHCP server - Happens at 87.5=% of lease time

Question 33

DNS Root

Answer 33

- Top of DNS hieararchy - Defined by . - 13 root levels, A-M

Question 34

DNS TLD

Answer 34

Top-level domain - Immediately below root in DNS hierarchy - Most prevalent are generic like .com, .org, .net, or .gove or .uk - Managed by ICANN and country-specific orgs

Question 35

DNS Information Process

Answer 35

- Trace records down from root through hierarchy - Root servers have complete information about TLD servers - TLD has information related to second-level domains - No name server has complete information for all domains