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Dynamic Host Configuration Protocol (DHCP)

DHCP has 2 ends, a client and a server.

DHCP Client: If configured to use DHCP, when a PC is connected to a network or powered on, it will send out a DHCP request, a broadcasted message asking for a networking configuration.
DHCP Server: When a DHCP server receives a DHCP request from a DHCP client, it leases an IP address and a network configuration to the DHCP client
A correctly configured DHCP server will be configured to be aware of IP address usage on the network and will not issue the same IP address to more than 1 device.

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Dynamic Host Configuration Protocol (DHCP)

An IP address and network configuration provided by a DHCP server is leased for a limited amount of time
When designing a network, you can choose the lease time from 1 second to 1 day to forever. Set the time to anticipate changes in the network.
When the lease expires, the DHCP client will ask the DHCP server to renew the network configuration.
The DHCP server can renew the same IP address or provide a different one.
With DHCP your IP address can change when the lease expires

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Working with DHCP (client)

ipconfig /release

Release leased IP address and network configuration
You will be disconnected from the network

ipconfig /renew

Send out a DHCP request
If a DHCP server is available and on the same network, it will provide an IP address and network configuration

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Working with DHCP (server)

On a home/small network DHCP will often be part of your router device
Hint: Usually typing in your gateway address into your web browser will bring up its configuration page
DHCP needs to have a pool defined

In the same IP address range/network as your LAN
A set of addresses that DHCP can lease to DHCP clients

Addresses can be reserved by MAC address

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Name resolution (DNS)

The primary system that we use on networks to “resolve names” is called DNS for domain name system (or service or server)
Networks use IP addresses to connect and not names
DNS is like a phone book that looks up the IP address(es) that is registered to a domain name
Tool to test DNS: nslookup (name server lookup)

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Working with DNS

Use nslookup to test DNS

> nslookup google.com

Server: UnKnown (name of the DNS server used to find IP)

Address: 10.61.0.2 (IP address of DNS server used to find IP)

Non-authoritative answer: (DNS server not original source of answer)

Name: google.com (Name we are resolving)

Addresses: 2607:f8b0:4005:80b::200e (google.com’s IPv6 address)

216.58.194.174 (google.com’s IPv4 address)

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Working with DNS

Use nslookup to test DNS

> nslookup google.com 9.9.9.9

Server: dns9.quad9.net (name of the DNS server used to find IP)

Address: 9.9.9.9 (IP address of DNS server used to find IP)

Non-authoritative answer: (DNS server not original source of answer)

Name: google.com (Name we are resolving)

Addresses: 2607:f8b0:4005:80b::200e (google.com’s IPv6 address)

172.217.5.110 (google.com’s IPv4 address)

Hmm… notice anything odd?

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Gateway / Routing

A gateway is your devices doorway outside of your LAN
Routing connects different networks together
For example your home router is connecting your local area network to Internet (WAN).
In enterprise networks routing can be used to connect separate LANs so that different groups of computers can communicate or share resources.

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Network Address Translation (NAT)

A system that translates a router's public IP address to the internal private IP addresses. Wikipedia.
Your computer has a private IP address and when it wants to communicate with the Internet, it sends a request to your gateway.
At the gateway that request passes between the private side of your network (LAN) and the public side (WAN) where your request is sent out.
Each outgoing request is mapped to each incoming response so that multiple device can share the same public IP address
A side effect of NAT is that messages that arrive at the public IP address that do not have a matching internal request are ignored - a kind of security.

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