CompTIA Network+ N10-006 - 1.3 Flashcards
DHCP Address Allocation
+ Dynamic allocation
- DHCP server has a big pool of IP addresses to give out.
- Address are reclaimed after a lease period.
+ Automatic allocation
- Similar to dynamic allocation
- DHCP server keeps a list of past assignments
- You’ll always get the same IP address
+ Static allocation
- Administratively configured
+ Table of MAC addresses
- Each MAC address has a matching IP address
+ Other names
- Static HDCP Assignment
- Static DHCP
- Address Reservation
- IP Reservation
DHCP Scopes
+ Grouping of IP addresses
- Each subnet has its own scope
- 192.168.1.0/24
- 192.168.2.0/24
- 192.168.3.0/24
- …
+ A scope is generally a single contiguous pool of IP addresses
- DHCP exceptions can be made inside of the scope.
Scope Properties
+ IP address range
+ Subnet mask
+ Lease durations
+ Other scope options
- DNS server
- Default gateway
- Windows server - configure all scopes subnet on the network.
DHCP leases
+ Leasing your address
- It’s only temporary
- But it can seem permanent
+ Allocation
- Assigned a lease time by the DHCP server
- Administratively configured
+ Reallocation
- Reboot your computer
- Confirms the lease
+ Workstation can also manually release the IP address
- Moving to another subnet
DHCP renewal
+ T1 timer
- Check in with the lending DHCP server to renew the IP address - 50% of the lease time (by default)
+ T2 timer
- If the original DHCP server is down, try rebinding with any DHCP server.
- 87.5% of the lease time (7/8ths)
i.e.
Lease Time: 8 days Renewal Timer (T1): 4 days (50%) Reminding Timer (T2): 7 days (87.5%)
DHCP options
+ A special field in the DHCP message
- Many, many options
+ Options are part of the DHCP RFC
- BOOTP called them “vendor extensions”
+ 256 (254 usable) options
- 0 through 255
- 0 is pad, 255 is end
+ Many common options
- Subnet mask, domain name server, domain name, etc.
+ Options are configured on the DHCP server
- Not all DHCP servers support option configuration
+ Options have been added through the years
- Option 120: Call Server IP address
- option 135: HTTP Proxy for phone-specific applications
Domain Name System
+ Translates human-readable names into computer-readable IP addresses
- You only need to remember www.ProfessorMesser.com, google.com, Netflix.com
+ Hierarchical
- Follow the path
+ Distributed database
- Many DNS servers
- 13 root server clusters
- Hundreds of generic top-level domains (gTLDs) - .com, .org, .net, etc.
- Over 275 country code top-level domains (ccTLDs) - .us, .ca, .uk, etc.
FQDN (Fully Qualified Domain Name)
All the devices below the hierarchy
DNS process
Resolver -> Local Name Server Root Server
Results are now cached
DNS records
+ Resource Records (RR)
- The database records of domain name services
+ Over 30 record types
- IP addresses, certificates, host alias names, etc.
Address records (A) (AAAA)
+ Defines the IP address of a host
- This is most queries
+ A records are for IPv4 addresses
- Modify the A record to change the host name to IP address resolution
+ AAAA (Quad A) records are for IPv6 addresses
- The same DNS server, different records
Www.professormesser.com. IN A 162.159.246.164 ; Professor Messer
^ (an A record)
IN = Internet
Canonical name records (CNAME)
• A name is an alias of another, canonical name
– One physical server, multiple services
; Alias (canonical) names
Gopher IN CNAME mail.mydomain.name.
Ftp. IN CNAME mail.mydomain.name.
Www. IN CNAME mail.mydomain.name.
IN = Internet
Mail exchanger record (MX)
• Determine the host name for the mail server
– This isn’t an IP address; it’s a name
Pointer record (PTR)
• The reverse of an A or AAAA record
– Added to a reverse map zone file
PTR = pointer
Dynamic DNS updating
• Dynamic DNS Update (DDNS)
– Update name server records with a secure, automated process
• DHCP means that address change all the time
–End-stations inform the DNS server of their IP address
• Part of Windows Active Directory
– Domain controllers register in DNS
– Allows other computers in the domain to find the AD servers
Dynamic DNS services
• Designed for SOHO dynamic IP addresses
– IP addresses are dynamically assigned by the ISP
• DDNS built into many SOHO routers
– Access your services from the internet
Proxy servers
• An intermediate server
– Client makes the request to the proxy
– The proxy performs the actual request
–The proxy provides results back to the client
• Useful features
–Access control, caching, URL filtering, content scanning
Forward proxy
[Internal Network] (User Proxy)
Then…
To internet
Reverse Proxy
You’re on the internet and need to connect to web server, send request to web server, web server responds to proxy, proxy responds to internet (me)
Open Proxy
Internet to proxy to internet
In order to remain anonymous. No IP address will be traced back.
S
Network Address Translation (NAT)
• IP address
– Your computer’s virtual location on the network
• Port number
– The services living inside of you computer
• You sometimes need to change this address and/or port
– Everyone needs to share one P address to the outside world
• Source NAT / PAT (Port Address Translation)
– Incoming requests need to redirected to a different IP address
• Destination NAT
• NAT generally includes both IP address and port number
– But it doesn’t have to
Destination NAT (DNAT)
• 24x7 access to a service hosted internally
– Web server, gaming server, etc.
• External IP/port number maps to an internal IP/port
– Does not have to be the same port number
• Also called port forwarding
– Destination address is translated from a public IP to a private IP
– Does not expire or timeout
• A static NAT
