VPN — Packet.School

A VPN builds an encrypted, private tunnel over an untrusted network like the internet. The name is the definition: virtual (no physical line), private (encrypted), network (it connects two ends).

code

[Your PC] ══════════════════════════ [Company network]
             Encrypted tunnel (VPN)
             across the internet

01What is a VPN used for?

1. Remote access

code

Home worker → VPN → company network

A computer at home reaches internal resources as if it were inside the office.

2. Site-to-site

code

Branch A → VPN tunnel → headquarters

Two offices talk as if a leased line ran between them.

3. Privacy

code

You → VPN server → internet

Sites you visit see the VPN server's IP, not yours.

4. Bypassing geo-restrictions

code

Home → US VPN → US catalog

Traffic appears to originate from another country.

02VPN protocols

Protocol	Security	Speed	Use
WireGuard	High	Very high	Next generation, the modern pick
OpenVPN	High	Medium	Most common, battle-tested
IPSec	High	Medium	Enterprise site-to-site
L2TP/IPSec	Medium	Low	Legacy systems
PPTP	Low	High	Broken — never use it!

03How does a VPN work?

1. Authentication

code

Client → username/password or certificate → VPN server

2. Tunnel setup

The original packet is encrypted and placed inside a new packet:

code

Original:
[IP Header][TCP][Data]
        ↓ encrypt and wrap
VPN packet:
[New IP][VPN Header][ encrypted(IP+TCP+Data) ]

Routers along the way only see the outer envelope; they can't read the contents. It's the Level 2 encapsulation idea — with encryption.

3. Data flow

code

Encrypted data → internet → VPN server → decrypted → onward to target

04VPN types

	Remote Access	Site-to-Site
Connects	One user to a network	Two networks to each other
Typical scenario	Working from home	Between branches
Common tech	SSL VPN, WireGuard	IPSec

05Split tunneling

Full tunnel: all traffic goes through the VPN — secure, but slower and heavy on the server.

Split tunnel: only company traffic enters the VPN; YouTube goes direct — fast, but possibly against company policy.

06What a VPN does and doesn't give you

It provides:

Encryption — nobody on the path can read your data
Authentication — both ends of the tunnel are verified
IP masking — target sites don't see your real IP

It does not provide:

Anonymity — the VPN provider can see your traffic
Malware protection — viruses travel through encrypted tunnels just fine
Legal invisibility — the provider may be keeping logs

07Summary

VPN = an encrypted tunnel over an untrusted network
Remote access and site-to-site are the two big scenarios
Modern picks: WireGuard or OpenVPN; stay away from PPTP
It gives encryption, it does not promise anonymity

code

[Your PC] ══════════════════════════ [Company network]
             Encrypted tunnel (VPN)
             across the internet

01What is a VPN used for?

1. Remote access

code

Home worker → VPN → company network

A computer at home reaches internal resources as if it were inside the office.

2. Site-to-site

code

Branch A → VPN tunnel → headquarters

Two offices talk as if a leased line ran between them.

3. Privacy

code

You → VPN server → internet

Sites you visit see the VPN server's IP, not yours.

4. Bypassing geo-restrictions

code

Home → US VPN → US catalog

Traffic appears to originate from another country.

02VPN protocols

Protocol	Security	Speed	Use
WireGuard	High	Very high	Next generation, the modern pick
OpenVPN	High	Medium	Most common, battle-tested
IPSec	High	Medium	Enterprise site-to-site
L2TP/IPSec	Medium	Low	Legacy systems
PPTP	Low	High	Broken — never use it!

03How does a VPN work?

1. Authentication

code

Client → username/password or certificate → VPN server

2. Tunnel setup

The original packet is encrypted and placed inside a new packet:

code

Original:
[IP Header][TCP][Data]
        ↓ encrypt and wrap
VPN packet:
[New IP][VPN Header][ encrypted(IP+TCP+Data) ]

Routers along the way only see the outer envelope; they can't read the contents. It's the Level 2 encapsulation idea — with encryption.

3. Data flow

code

Encrypted data → internet → VPN server → decrypted → onward to target

04VPN types

	Remote Access	Site-to-Site
Connects	One user to a network	Two networks to each other
Typical scenario	Working from home	Between branches
Common tech	SSL VPN, WireGuard	IPSec

05Split tunneling

Full tunnel: all traffic goes through the VPN — secure, but slower and heavy on the server.

Split tunnel: only company traffic enters the VPN; YouTube goes direct — fast, but possibly against company policy.

06What a VPN does and doesn't give you

It provides:

Encryption — nobody on the path can read your data
Authentication — both ends of the tunnel are verified
IP masking — target sites don't see your real IP

It does not provide:

Anonymity — the VPN provider can see your traffic
Malware protection — viruses travel through encrypted tunnels just fine
Legal invisibility — the provider may be keeping logs

07Summary

VPN = an encrypted tunnel over an untrusted network
Remote access and site-to-site are the two big scenarios
Modern picks: WireGuard or OpenVPN; stay away from PPTP
It gives encryption, it does not promise anonymity