Introduction
While studying for CompTIA Network+, many network protocols made me messed up.
It confused me a lot because of the similar names such as LACP, LLDP, L2TP, and LDAP.
I didn't understand each name and how they act in network.
Once I understood why each one existed, everything fell into place. So, I decided to write it down.
Overview table
| Protocol | Purpose | Layer | Similar example |
|---|---|---|---|
| LACP | Bundle cables | Layer 2 | 1 Lane→4 Lanes |
| LLDP | Discover adjacent devices | Layer 2 | Greet neighbor |
| L2TP | Create VPN tunnel | Layer 2 | Sending a letter in an envelop |
| LDAP | Manage user authentication | Layer 7 | One staff ID card opens all doors |
LACP ( Link Aggregation Control Protocol )
Understanding in a nutshell
This protocol is a mechanism that bundles multiple cables into a single logical link.
Why it is needed
Problem：
Only one cable limits the speed (Maximum 1 Gbps)
The connection will be stopped, if it breaks down.
Solution：
Bundle multiple cables
→ Accelerate the speed
→ Continue to connect, if a cable breaks down.
Familiar example
One lane road （A normal cable）
→ Cause traffic jam, which slow the speed down
→ Impossible to function by accident or construction work
Four lane roads（ Bundle four cables by LACP）
→ Avoid the cause of congestion
→ Possible to function by accident or construction work due to the presence of other lanes
Specific structure
Normal：
Switch ──── 1Gbps ──── Server
↑
Only one cable
LACP：
┌── 1Gbps ──┐
Switch ──────┼── 1Gbps ──┼───── Server
├── 1Gbps ──┤
└── 1Gbps ──┘
Total 4Gbps（Logically one cable)
2 main pros
1. Expand bandwidth
→ Logically four times as fast as only one cable, if four cables are bundled.
2. Ensure redundancy
→ The remaining cables enable maintain the connection even if one cable fails.
→ Endure technical issues
LLDP ( Link Layer Discovery Protocol )
Understanding in a nutshell
** This protocol automatically discovers information about neighboring devices.**
Why it is needed
Problem：
In a large scale network, it is hard to grasp that where devices are connected
Solution：
Devices automatically tell adjacent devices the own information each other
Familiar example
When you move home
→ You don't find the people who live next door
→ Greeting makes you understand who he or she is
Without LLDP
→ Manager have to confirm each device by hand
With LLDP
→ Each device automatically tell their information each other
→ Managers can understand the entire network structure without leaving their desk
Information it can collect
・Name of the device
・Kind of the device ( Switch, Router etc. )
・Port number
・IP address
・Manufacturer
Use case
Troubleshooting：
→ Instant check "Which device is connected to this port"
Network management：
→ Connect to the tool that automatically create configuration diagram
Replace device：
→ New device automatically introduces itself to adjacent devices
L2TP ( Layer 2 Tunneling Protocol )
Understanding in a nutshell
This protocol creates a virtual tunnel over the Internet to enable secure communication
Why it is needed
Problem：
Possible to leak important information to the Internet
Solution：
Create virtual tunnel and send data within the tunnel
→ Disabled to see the data from outside
Familiar example
Normal internet connection：
→ Send with a postcard
→ Anyone can read the content
L2TP tunnel：
→ Send with an envelop
→ No one can read the content
→ Reach to the destination securely
Specific structure
Home PC
↓
Internet（ Public line ）
↓ L2TP tunnel（ Virtual dedicated line）
Office network
See from outside：
→ Cannot see inside data
→ Just like working at the office
Combination with IPsec
Only L2TP：
→ Just create tunnel
→ Without encryption
L2TP/IPsec：
→ Tunnel + Encryption
→ More secure VPN connection
→ In practice, they are almost always used together
LDAP ( Lightweight Directory Access Protocol )
Understanding in a nutshell
This protocol is a mechanism that centrally manage user information and use them for authentication
Why it is needed
Problem：
A lot of login information are needed if there are many system
→ Hard to manage multiple passwords
Solution：
Collect user information in one place and manage it centrally
Familiar example
Without LDAP：
→ Separately manage several information such as Admission badge, PC password, mail password, system password
→ Both managers and users are hard to manage them
With LDAP：
→ Only one ID and password enables users to login all systems
→ Admission badge makes us possible unlock all doors
Specific structure
PC（ Require login）
↓
LDAP server（ Active Directory etc.）
↓ " Has this user already been registered?"
↓ " Has this user had which role?"
↓
Authentication succeed → User can access the system
Authentication failed → User cannot access the system
What is Directory
Directory in LDAP is like address list for user information
Registered information：
・Name
・Mail address
・Department
・Password（ Hashed ）
・Role（ Common user or manager ）
Relationship with Active Directory
LDAP ：A protocol（ a set of communication rules ）
Active Directory： A Microsoft product that uses LDAP internally
LDAP is one of network protocols that Active Directory uses
Organize 4 protocols difference
LACP： Enhance physical connection
→ Speed up and enforce redundancy by bundling cables
LLDP： Automatically identify network topology
→ Automatically research what the adjacent device is
L2TP：Securely connect with remote area
→ Create virtual tunnel in the Internet
LDAP： Manage users
→ Centrally manage user authentication
Relationship with OSI reference model
Layer 7 Application ← Where LDAP operates
Layer 6 Presentation │
Layer 5 Session │
Layer 4 Transport │
Layer 3 Network │
─────────────────────────────
Layer 2 Data Link ← Where LACP・LLDP・L2TP operate
Layer 1 Physical │
─────────────────────────────
Summary ( repost )
| Protocol | Purpose | Layer | Similar example |
|---|---|---|---|
| LACP | Bundle cables | Layer 2 | 1 Lane→4 Lanes |
| LLDP | Discover adjacent devices | Layer 2 | Greet neighbor |
| L2TP | Create VPN tunnel | Layer 2 | Sent letter in an envelop |
| LDAP | Management user authentication | Layer 7 | Open all doors with an staff identity card |
Conclusion
In this article, I covered four protocols that are easy to confuse due to their similar names. Once I understood the purpose behind each one, everything clicked. I hope this helps anyone else who is struggling with the same confusion.
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