diff --git a/13. Subnetting (Part 1).md b/13. Subnetting (Part 1).md index 90de4e7..27a34ed 100644 --- a/13. Subnetting (Part 1).md +++ b/13. Subnetting (Part 1).md @@ -1,194 +1,178 @@ --- + id: 1777840095-WYOD aliases: - - Subnetting (Part 1) -tags: - - CCNA ---- + +* Subnetting (Part 1) + tags: +* CCNA # Subnetting (Part 1) -## IPV4 Address Classes +## IPv4 Address Classes -| Class |First octet | numeric range | Prefix Length | -| ----- | ---------- | ------------- |------------- | -| A |0xxxxxxxx | 0-127 | /8 | -| B |10xxxxxxx | 128-191 | /16 | -| C |110xxxxxx | 192-223 | /24 | -| D |1110xxxxx | 224-239 | | -| E |1111xxxxx | 240-255 | | +| Class | First Octet (Binary) | Range | Default Prefix | +| ----- | -------------------- | ------- | --------------- | +| A | 0xxxxxxx | 0–127 | /8 | +| B | 10xxxxxx | 128–191 | /16 | +| C | 110xxxxx | 192–223 | /24 | +| D | 1110xxxx | 224–239 | N/A (Multicast) | +| E | 1111xxxx | 240–255 | N/A (Reserved) | +--- -### Maximum Hosts per Network +## Maximum Hosts per Network -Host portion all 0s = Network address (network ID) -Host portion all 1s = broadcast address +* Host bits all **0s** → Network address +* Host bits all **1s** → Broadcast address -192.168.1.0/24 -> 192.168.1.255/24 -Host portion = 8 bits = 2^8 = 256 -Maximum hosts per network = 2^8-2 = 254 +### Example Calculations +**192.168.1.0/24 → 192.168.1.255** -172.16.0.0/16 -> 172.16.255.255/16 -Host portion = 16 bits = 2^16 = 65,536 -Maximum hosts per network = 2^16 -2 = 254 +* Host bits: 8 +* Total addresses: 2⁸ = 256 +* Usable hosts: 256 − 2 = **254** -10.0.0.0/8 -> 10.255.255.255/8 -Host portion = 24 bits = 2^24 = 16,777,216 -Maximum hosts per network = 2^24 -2 = 16,777,214 +**172.16.0.0/16 → 172.16.255.255** -### How IP addresses are distrubuted +* Host bits: 16 +* Total addresses: 2¹⁶ = 65,536 +* Usable hosts: 65,536 − 2 = **65,534** -- The [[IANA]] (Internet Assigned Numbers Authority) assigns IPV4 addresses/networks to -companies based on their size -- For example, a very large company might receive a class A or class B network, while a small -company might receive a ckass C network. -- However, this led to many wasted IP addresses. +**10.0.0.0/8 → 10.255.255.255** -#### Example 1 +* Host bits: 24 +* Total addresses: 2²⁴ = 16,777,216 +* Usable hosts: 16,777,216 − 2 = **16,777,214** -+----+ +----+ -| R1 |<----->| R2 | -+----+ ^ +----+ - Point to Point network - - 256 addresses - - 1 network address (203.0.113.0) - - 1 broadcast address (203.0.113.255) - - 1 R1 address (203.0.113.1) - - 1 R2 address (203.0.113.2) - - **252 addresses Wasted** +--- +## How IP Addresses Were Distributed -#### Example 2 +* The **IANA (Internet Assigned Numbers Authority)** originally allocated IP ranges based on class. +* Large organizations received Class A or B networks, while smaller ones received Class C. +* This rigid system caused significant address waste. -Company X needs IP addressing for 5000 end hosts. -- A class C network does not provide enough addresses, so a class B network must be assigned -- This will result in about 6000 addresses being wasted. +### Example 1: Point-to-Point Link -## CIDR +Network: 203.0.113.0/24 -- When the internet was first created, the creators did not predict that the internet -would become as large as it is today -- This resulted in wasted address space like the examples. -- The [[IETF]] introduced [[CIDR]] in 1993 to replace the 'classful' addressing system. -- With CIDR, the requirement of ... - - Class A = /8 - - Class B = /16 - - Class C = /24 -were removed -- This allowed larger networks to be split into smaller networks, allowing greater efficiency -- These smaller networks are called 'subnetworks' or [[subnetting]] +* Total addresses: 256 +* Used: -+----+ +----+ -| R1 |<----->| R2 | -+----+ ^ +----+ - 203.0.113.0/24 + * Network: 203.0.113.0 + * Broadcast: 203.0.113.255 + * R1: 203.0.113.1 + * R2: 203.0.113.2 +* **Unused: 252 addresses** -Network address -11001011.00000000.01110001.*00000000* - 203 . 0 . 113 . 0 +A tiny road, but a massive parking lot sitting empty. -Subnet Mask -11111111.11111111.11111111.*00000000* - 255 . 255 . 255 . 0 +--- -2^8 - 2 = 254 usable addresses. +### Example 2: Company Needs 5000 Hosts -How many usable addreses are there in each network? +* Class C → too small (254 hosts) +* Class B → required (65,534 hosts) +* Result: ~60,000 unused addresses -#### CIDR /25 -**203.0.113.0/25** -Network address: -11001011.00000000.01110001.0*0000000* - 203 . 0 . 113 . 0 -Subnet Mask -11111111.11111111.11111111.1*0000000* - 255 . 255 . 255 . 128 -*2^7 - 2 = 126 usable addresses* +--- -#### CIDR /26 -**203.0.113.0/26** -Network address -11001011.00000000.01110001.00*000000* - 203 . 0 . 113 . 0 -Subnet Mask -11111111.11111111.11111111.11*000000* - 255 . 255 . 255 . 192 -*2^6 - 2 = 62 usable addresses* +## CIDR (Classless Inter-Domain Routing) -#### CIDR /27 -**203.0.113.0/27** -Network address -11001011.00000000.01110001.00*000000* - 203 . 0 . 113 . 0 -Subnet Mask -11111111.11111111.11111111.111*00000* - 255 . 255 . 255 . 224 -*2^5 - 2 = 30 usable addresses* +* Introduced by the **IETF (Internet Engineering Task Force)** in 1993 +* Replaced classful addressing +* Removed fixed boundaries: -#### CIDR /28 -**203.0.113.0/28** -Network address -11001011.00000000.01110001.00*000000* - 203 . 0 . 113 . 0 -Subnet Mask -11111111.11111111.11111111.1111*0000* - 255 . 255 . 255 . 240 -*2^4 - 2 = 14 usable addresses* + * Class A = /8 + * Class B = /16 + * Class C = /24 -#### CIDR /29 -*203.0.113.0/29* -Network address -11001011.00000000.01110001.00000*000* - 203 . 0 . 113 . 0 -Subnet Mask -11111111.11111111.11111111.11111*000* - 255 . 255 . 255 . 248 -*2^4 - 2 = 6 usable addresses* +### Why CIDR Matters -#### CIDR /30 -**203.0.113.0/30** -Network address -11001011.00000000.01110001.000000*00* - 203 . 0 . 113 . 0 -Subnet Mask -11111111.11111111.11111111.111111*00* - 255 . 255 . 255 . 252 -*2^4 - 2 = 6 usable addresses* +CIDR lets you carve networks like a careful sculptor instead of swinging a sledgehammer. +Large networks can be split into smaller, efficient subnets. -This is the perfect CIDR for our 2 router +--- -The remaining addresses in the 20 203.0.113.0/24 address block (20 203.0.113.4 - 20 203.0.113.255) -are now available to be used in other subnets! +## Subnetting Example -#### CIDR /31 -*203.0.113.0/31* +Base network: **203.0.113.0/24** -2^1 -2= 0 usable addresses +* Subnet mask: 255.255.255.0 +* Usable hosts: **254** -but for our point to point connection we can utilisize it -no need for broadcast or network address -In cisco device however you get a systeme warning +--- + +## CIDR Subnet Breakdown + +### /25 + +* Mask: 255.255.255.128 +* Hosts: 2⁷ − 2 = **126** + +### /26 + +* Mask: 255.255.255.192 +* Hosts: 2⁶ − 2 = **62** + +### /27 + +* Mask: 255.255.255.224 +* Hosts: 2⁵ − 2 = **30** + +### /28 + +* Mask: 255.255.255.240 +* Hosts: 2⁴ − 2 = **14** + +### /29 + +* Mask: 255.255.255.248 +* Hosts: 2³ − 2 = **6** + +### /30 + +* Mask: 255.255.255.252 +* Hosts: 2² − 2 = **2** + +✔ Ideal for point-to-point links (e.g., router-to-router) + +--- + +### /31 + +* Hosts: 2¹ − 2 = 0 (traditionally) + +However: + +* Used for point-to-point links +* No network or broadcast needed + +Cisco warning example: ```cisco Router(config-if)# ip address 203.0.113.0 255.255.255.254 -Warning use /31 mask on non point-to-pint interface cautiously +Warning: use /31 mask on non point-to-point interface cautiously ``` -The remaining addresses in the 20 203.0.113.0/24 address block (20 203.0.113.2 - 203.0.113.255) -are now available to be used in other network! +--- +### /32 -#### CIDR /32 -*203.0.113.0/32* +* Hosts: 2⁰ − 2 = −1 (conceptually) -2^1 -2= -1 usable addresses +Used for: -can be used in static routes -don't worry about them now +* Loopbacks +* Static routes +* Identifying a single host -## Review +--- -- [[CIDR]] (Classless Inter-Domain Routing) -- The process of subnetting +## Key Takeaways +* CIDR enables flexible and efficient IP allocation +* Subnetting reduces waste and improves scalability +* Smaller subnets = better utilization of address space