🖥️ Private IP vs Public IP Address

 

IPv4 Address Class Ranges

ClassFirst Octet RangeFull IP RangePurpose
Class A1 – 1261.0.0.0 – 126.255.255.255    Large networks
Class B128 – 191128.0.0.0 – 191.255.255.255    Medium networks
Class C192 – 223192.0.0.0 – 223.255.255.255    Small networks
Class D224 – 239224.0.0.0 – 239.255.255.255    Multicast
Class E240 – 255240.0.0.0 – 255.255.255.255    Experimental/Reserved

Private IP : 

Class A - 10.0.0.0 - 10.255.255.255
Class B - 172.16.0.0 - 172.31.255.255
Class C - 192.168.0.0 - 192.168.255.255

🖥️ Private IP vs Public IP Address

🧠 Definition:

  • Private IP Address:
    Used inside a private network (LAN) — identifies devices like PCs, printers, and routers within a local area.
    Example: 192.168.1.10

  • Public IP Address:
    Used on the Internet — identifies your network or device globally so it can communicate with other networks.
    Example: 8.8.8.8

🔹 Key Differences

FeaturePrivate IP AddressPublic IP Address
ScopeUsed within local/private networksUsed on the Internet (global scope)
UniquenessCan be reused in different networksMust be unique worldwide
Assigned byNetwork Administrator or Router (DHCP)Internet Service Provider (ISP)
AccessibilityNot reachable from the InternetReachable over the Internet
SecurityMore secure, hidden from external accessLess secure, visible on the Internet
Example Ranges10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255		1.0.0.0 – 223.255.255.255 (except private ranges)

💡 Quick Example

At home or school:

  • Private IP (Internal): 192.168.1.5 → Your laptop

  • Public IP (External): 122.175.34.10 → Your network’s router (assigned by ISP)

When you visit a website, your router uses NAT to translate your private IP into the public IP for communication.

💬 Teaching Tip

“Think of a Private IP as your house address inside a housing society, and the Public IP as the main gate address of the society — the world only knows that gate, not each house inside.”

IPv6 

128 bit address
 
Maximum IPv6 addresses:

2128≈3.4×10382^{128}\approx3.4\times10^{38}

2001:0db8:85a3:0000:0000:8a2e:0370:7334


Current Situation

IPv4

  • Still used by most networks and websites.
  • Most home routers and enterprise networks support IPv4.
  • Example: 
192.168.1.10

IPv6

  • Adoption is steadily increasing.
  • Many ISPs, mobile networks, and large websites support IPv6.
  • Example: 
2001:db8::1


or the CCNA exam, you don't need to memorize every IPv6 address type, but you must understand the important ones. Here's a clear guide.

1. Unspecified Address



::

Meaning



    

  • 
Equivalent to 0.0.0.0 in IPv4.

    • 

  • 
Means "I don't have an IPv6 address yet."

    •

Used by



    

  • 
A device during startup before obtaining an IPv6 address.

    •

2. Loopback Address ⭐



::1

Meaning



    

  • 
Equivalent to 127.0.0.1 in IPv4.

    • 

  • 
Used to test the local TCP/IP stack.

    • 



Example:


ping ::1

3. Global Unicast Address ⭐⭐⭐



Starts with:


2000::/3


Examples:


2001:db8:1::10

2401:4900:1234::1

Purpose



    

  • 
Public IPv6 addresses.

    • 

  • 
Routable across the Internet.

    • 



Equivalent to:


IPv4 Public Address

4. Link-Local Address ⭐⭐⭐



Starts with:


FE80::/10


Example:


FE80::1

Purpose



    

  • 
Automatically created on every IPv6-enabled interface.

    • 

  • 
Used for communication on the local link only.

    •

Important Facts



    

  • 
Never routed by routers.

    • 

  • 
Used by routing protocols and for neighbor discovery.

    • 



Equivalent to an automatic local communication address.

5. Unique Local Address (ULA)



Starts with:


FC00::/7


Most commonly:


FD00::/8


Example:


FD12:3456:789A::1

Purpose



    

  • 
Private IPv6 addressing.

    • 

  • 
Used inside organizations.

    • 



Equivalent to IPv4 private addresses such as:


    

  • 
10.0.0.0/8

    • 

  • 
172.16.0.0/12

    • 

  • 
192.168.0.0/16

    •

6. Multicast Address ⭐⭐⭐



Starts with:


FF00::/8


Example:


FF02::1

Purpose



Send one packet to multiple devices.


IPv6 does not use broadcast. Instead, it uses multicast.

Common Multicast Addresses

All Nodes



FF02::1


Every IPv6 device joins this group.

All Routers



FF02::2


Every IPv6 router joins this group.

7. Anycast Address



An anycast address is assigned to multiple devices.


The packet is delivered to the nearest device according to the routing table.


Commonly used for:


    

  • 
DNS servers

    • 

  • 
CDN services

    • 

  • 
Cloud services

    •

8. Solicited-Node Multicast ⭐



Example:


FF02::1:FFxx:xxxx


Purpose:


    

  • 
Used during IPv6 address resolution (Neighbor Discovery).

    • 

  • 
Replaces IPv4 ARP broadcasts.

    • 






Address TypePrefixIPv4 EquivalentInternet RoutablePurpose
Global Unicast2000::/3Public IP✅ YesInternet communication
Unique LocalFC00::/7 (FD00::/8)Private IP❌ NoInternal networks
Link-LocalFE80::/10No direct IPv4 equivalent (APIPA is somewhat similar)❌ NoSame-link communication, Neighbor Discovery
MulticastFF00::/8IPv4 Multicast (224.0.0.0/4)Depends on scopeOne-to-many communication

1. Global Unicast Address (GUA)

Purpose: Used for communication over the Internet. It is the IPv6 equivalent of a public IPv4 address.

Prefix

2000::/3

This means the address starts with:

  • 2xxx
  • 3xxx

Example

2001:db8:1::10/64

Characteristics

  • Globally unique
  • Routable on the Internet
  • Assigned by an ISP or organization

Example

PC1
2001:db8:1::10
        │
        │
Router
2001:db8:1::1
        │
     Internet

2. Unique Local Address (ULA)

Purpose: Used only inside private networks. Similar to private IPv4 addresses (192.168.x.x, 10.x.x.x).

Prefix

FC00::/7

Most commonly:

FD00::/8

Example

FD12:3456:789A::10

Characteristics

  • Private
  • Not routable on the Internet
  • Used within organizations

Example

Office LAN

PC1
FD00:1::10
      │
      │
Router
FD00:1::1

3. Link-Local Address

Purpose: Used for communication on the same local network segment. Routers do not forward these addresses.

Prefix

FE80::/10

Example

FE80::1

Characteristics

  • Automatically assigned
  • Every IPv6 interface has one
  • Used for:
    • Neighbor Discovery (replaces ARP)
    • Router discovery
    • Routing protocol neighbor relationships (OSPFv3, EIGRP for IPv6)

Example

PC1
FE80::10
      │
Switch
      │
Router
FE80::1

Communication works only on this local link.

4. Multicast Address

Purpose: Send one packet to multiple devices.

IPv6 does not use broadcast. It uses multicast instead.

Prefix

FF00::/8

Common Multicast Addresses

AddressPurpose
FF02::1All IPv6 nodes
FF02::2All IPv6 routers
FF02::5OSPFv3 routers
FF02::AEIGRP routers


IPv4 vs IPv6 Comparison



IPv4IPv6
0.0.0.0::
127.0.0.1::1
Public IP2000::/3
Private IPFC00::/7 (commonly FD00::/8)
APIPA 169.254.x.xFE80::/10 (Link-Local)
Broadcast❌ Not used
MulticastFF00::/8

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