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By: Iselin
November 24, 2018

Networking part 2 DNS DHCP MAC

By: Iselin
November 24, 2018
By: Iselin
November 24, 2018

Networking Part 2

DNS

“The human name of IP addresses”Allows the computer to translate human names to IP addresses

In order to make it easier to browse the web more efficiently, we translate our destination addresses to Domain Names. 172.217.20.46 is the address for www.google.com for instance, but they both represent the same destination. This is just to make it easier to remember web pages.

It operates on port 53:TCP/UDP

.com ← root domain (.org, .net .no .us)google ← Domain namegoogle.com ← Fully qualified Domain Name (FQDN)

 

Internal DNS addresses /names

“The saved locations for later use”

Internal DNS names and addresses are used to fetch addresses more quickly.

If the internal DNS server doesn't find the location in its local manual configuration, we set 8.8.8.8 as our “default gateway” and ask the exterior network to find it. When finding and browsing the new page, our internal DNS will save the IP and FQDN in the cache. This will make it quicker to find the destination next time we request it. The infamous ipconfig/ flushdns command will flush our DNS cache.

 

DNS Servers main functions

Auto update records, monitors changes, may not give everyone permission of use for security measures and DNS Resolution which is the translation from an IP address to a Fully Qualified Domain Name or vice versa.

 

Media Access Control

“A device’s permanent physical name”The physical address of which “device” it is. Unique addresses all over the worldHexadecimal 0-9 A-F (AB-01-37-BC-78-BF / AB:01:37:BC:78:BF)MAC addresses allow us to make data link connections as well as point to point connections that are not routed through any router. MAC is like a permanent name to a device that doesn’t change. It is a physical address.

 

Default Gateway

Where to go to get out of the network”Only addresses packets that are directly sent to the router. Default Gateway is the address used to go outside of the interior network and out into the exterior.192.168.1.1 - 255.255.255.0

Dynamic Host Configuration Protocol

Allows us to configure range of Host IDs (192.168.1.0-50 for example)Allows us to configure a temporary IP “lease lengthy expiration”

Allows us to reserve static IP addresses that are not to be changed (this is reserved on the device’s MAC address)Allows us to configure default gatewayAllows us to configure a DNSRuns on protocol 67(Server)68(Client): UDP

 

The process:1. DHCP Discover (sending a broadcast message any direction asking “I need an IP address”)2. Response back3. Home router sends offer to computer4. Computer sends acknowledgement to the offer5. Router says good to go

 

DHCP Scope

“a range of IP addresses that can be leased to DHCP clients on a given Subnet”

This is useful to narrow down ranges that are unused in a subnet. For example, 192.168.50-200. We usually follow the 80/20 rule when we have two DHCP servers. This means that server 1 (main server) may have 80% of the scope, while server 2 (secondary server) has 20%. This is useful in case one server fails and we would still be able to use the other.

DHCP Leases

How long the address will be valid”

A DHCP lease is the amount of time the given IP will be good for. The Device will attempt renewal of address after 87.5% of the lease is left. If the DHCP turns the request down, it will ask again until a closer percentage appears over again until renewal.

DHCP Options

“Codes/numbers on a client that are coded into the network settings”

• 050: IP Address (if we have an IP reservation, we specify this Mac address' IP address)• 051: Lease time• 006: DNS Servers (one or more servers to put into the settings)• 003: default gateway (next location to send information)• 001: subnet mask• 015: domain name (suffix. if connected to a network with a DHCP server providing information, it provides with domain name settings)

 

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