Domain 1.6 Flashcards
Describe the four step DHCP process
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.
True or False: DHCP requests will be answered if there is no DHCP server on the subnet
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.
How do DHCP Servers respond to Discover requests that are not on the same subnet.
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.
What are the properties that are configured in a DHCP scope
IP Address range
IP Address Exclusions
Subnet Mask
Lease duration
DNS server
Gateway information.
What is a DHCP pool
Grouping of IP addresses
Each subnet will have its won scope and scope options.
Scope will normally be a contiguous pool of IP addresses
What are the three DHCP assignment methods
Dynamic
Automatic
Static
Describe the Dynamic DHCP Address Assignment method
DHCP Server has a large pool of addresses.
Addresses are leased to and returned by the host following the four step process (DORA)
Describe the Automatic DHCP Address Assignment method
Similar to Dynamic, DHCP server keeps list of past assignments, and provides the same IP address to hosts every time
Describe the Static DHCP Address Assignment method
Administratively configured table of MAC addresses. Each MAC address has its own IP Address.
AKA “IP Reservation, Static Assignment”
What is a T1 Timer?
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.
What is a T2 Timer
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.
compare Internal and External DNS
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
What are the type of DNS lookups
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
what is a recursive DNS Query
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
What is an Iterative DNS query
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.
What are the different DNS record types
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)
What is a resource record
The database records of domain name services
Over 30 types IP address, Certificates, host alias names
Describe an SOA
Start of Authority -
Record that describes the DNS Zone Details
Structure -
IN SOA (Domain Name)
-Serial Number
- Refresh, Retry Time Frames
-Caching Duration/TTL
Describe both A and AAAA records
Address records
A = IPv4
AAAA - IPV6
Defines the IP address of a host
- Most popular query
Describe a CNAME Record
A name is an alias of another canonical name
Used when you have a single physical server that has multiple services running on it.
Describe a Service Record
Record that finds a specific service offered on a server.
Describe an MX record
Mail Exchanger Record -
Determines the host name for the mail server
Not an IP address, just a name
Describe an NS record
Name Server Record -
list the name servers for a domain, NS records point to the name of the server.
Describe a PTR record
The reverse of a A or AAAA record.
Added to a reverse map zone file.
Describe a TXT record
Human readable text information that can be used for showing public information.
SPF and DKIM information can be stored in a PTR record.
What is SPF
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.
What is DKIM
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.
Describe a zone transfer
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.
What port does NTP run on
UDP/123
What are the different NTP toplogies
NTP Server
NTP Client
NTP Client/Server
Describe NTP Clients and Servers
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
What does an NTP Client/Server do
Requests time updates from NTP servers.
Responds to time requests from other NTP clients
What is a Stratum
A number assocaited with the distance a NTP client is from the original NTP reference clock.
What is Stratum 0 mean
A very reliable NTP clock.
Atomic, or GPS clock
What is Stratum 1 Mean
A clock that is syncd with a Stratum 0 clock. Used for a primary time server
What is a Stratum 2
A clock that is synched with a Stratum 1 server
