Add linting rules with markdownlint-cli

.markdownlint.yml

@@ -0,0 +1,19 @@
+default: true
+
+# Spaces for indent
+MD007:
+  indent: 4
+
+# Line length
+MD013: false
+
+# Multiple headings with the same content
+MD024:
+  siblings_only: true
+
+# Inline HTML
+MD033: false
+
+# Images should have alternate text (alt text)
+MD045: false
+

.pre-commit-config.yml

@@ -0,0 +1,6 @@
+repos:
+
+- repo: https://github.com/igorshubovych/markdownlint-cli
+  rev: v0.40.0
+  hooks:
+  - id: markdownlint

README.md

@@ -2,8 +2,8 @@
 
 Personal notes for learning [CCNA](https://www.cisco.com/site/us/en/learn/training-certifications/certifications/enterprise/ccna/index.html) topics.
 
-
 ## Contents
+
 * [Network Devices](./contents/network_devices/)
 * [Interfaces and Cables](./contents/interfaces_and_cables/)
 * [OSI model and TCP/IP suite](./contents/osi_model_and_tcp_ip_suite/)
@@ -14,14 +14,12 @@ Personal notes for learning [CCNA](https://www.cisco.com/site/us/en/learn/traini
 * Routing
     * [IPv4 Header](./contents/ipv4_header/)
 
-
 ## Network node icons
 
 The following are the icons use in some diagrams from [Jeremy's IT Lab](https://www.youtube.com/playlist?list=PLxbwE86jKRgMpuZuLBivzlM8s2Dk5lXBQ) I used in this repo:
 
 ![Icon used in various diagrams and examples](/docs/node_icons.png)
 
-
 ## Sources
 
-* [Jeremy's IT Lab](https://www.youtube.com/playlist?list=PLxbwE86jKRgMpuZuLBivzlM8s2Dk5lXBQ)
+* CCNA Course from [Jeremy's IT Lab](https://www.youtube.com/playlist?list=PLxbwE86jKRgMpuZuLBivzlM8s2Dk5lXBQ)

contents/ethernet_lan_switching/README.md

@@ -1,28 +1,27 @@
 # Ethernet LAN Switching
 
-
 ## Table of contents
-* [What is a LAN ?](#what-is-a-lan)
+
+* [What is a LAN ?](#what-is-a-lan-)
 * [Ethernet Frame](#ethernet-frame)
 * [MAC Address](#mac-address)
 * [ARP](#arp)
 * [Ping](#ping)
 * [MAC Address Table](#mac-address-table)
 * [Examples](#examples)
 
-
 ## What is a LAN ?
+
 A Local Area Network is a network contained within a relatively small area.
 LANs use L2 layer frames.
 
 ![](docs/some_LANs.png)
 
-
 ## Ethernet Frame
 
 ![A complete ethernet frame structure](docs/ethernet_frame.png)
 
-* 26 bytes 	🔥
+* 26 bytes  🔥
 
 * `HEADER`
     * 22 bytes
@@ -35,7 +34,7 @@ LANs use L2 layer frames.
 * `TRAILER`
     * 4 bytes
     * `FCS` (Frame Check Sequence): used by the receiving device to detect any errors that may have occurred in transmission
-    
+
 ![Preamble + SFD are usually not considered part of the ethernet header](docs/ethernet_frame_without_preamble_n_sfd.png)
 
 * 18 bytes without Preamble + SFD 🔥🔥🔥
@@ -44,29 +43,25 @@ LANs use L2 layer frames.
 * 64 bytes - 18 bytes (header + trailer) = 46 bytes for the **packet** (minimum)
 * if payload is less than 46 bytes, padding bytes are added
 
-
 ### Preamble
 
 * 7 bytes (8 bits * 7 = 56 bits)
 * 10101010 * 7
 * Allows deviced to sync their receiver clocks
 
-
 ### SDF (Start Frame Delimiter)
 
 * 1 bytes (8 bits)
 * 10101011
 * Marks the end of the preable, and the beginning of the rest of the frame
 
-
 ### Destination and Source
 
 * 6 bytes each (8 bits * 6 = 48 bit) address of physical device
 * indicate the devices sending and receiving the frame
 * consist of destination and source `MAC address`
 * `MAC` = Media Access Control
 
-
 ### Type / Length
 
 * 2 bytes (8 bits * 2 = 16 bits)
@@ -76,14 +71,12 @@ LANs use L2 layer frames.
 * IPv6 = 0x86DD (Hexadecimal) = `34525` in decimal
 * ARP Packet = 0x0806 (Hexadecimal) = `2054` in decimal
 
-
 ### FCS (Frame Check Sequence)
 
 * 4 bytes (32 bits) in length
 * detects corrupted data by running a *"CRC"* algorithm over the receiving data
 * `CRC`: "Cyclic Redundancy Check"
 
-
 ## MAC Address
 
 * 6 bytes (48 bits) physical address assigned to the device when it is made
@@ -93,7 +86,6 @@ LANs use L2 layer frames.
 * Last 3 bytes are unique to the device itself 🔥
 * Written as 12 **hexadecimal** characters
 
-
 ## ARP
 
 * stands for Address Resolution Protocol
@@ -105,7 +97,6 @@ LANs use L2 layer frames.
 * `ARP Reply` is a `unicast` ethernet frame
 * **broadcast** MAC address used in **ARP Request** is FF.FF.FF.FF.FF.FF
 
-
 ### ARP Table
 
 Use `arp -a` to view the ARP table and show all ARP entries
@@ -115,7 +106,6 @@ Use `arp -a` to view the ARP table and show all ARP entries
 * `type static`: default entries
 * `type dynamic`: learned via ARP
 
-
 ## Ping
 
 * network utility used to test reachability
@@ -131,12 +121,10 @@ In the above example the first of the 5 requests sent failed because of ARP.
 
 ![](docs/wireshark_ping.png)
 
-
 ### Cisco IOS ARP
 
 ![](docs/ios_show_arp.png)
 
-
 ## MAC Address Table
 
 To **show** the MAC Address table in CISCO devices use:
@@ -151,7 +139,6 @@ To manually **clear** the MAC Address table in CISCO devices use:
 
 ![](docs/clear_mac_address.png)
 
-
 ## Examples
 
 ### Example 1
@@ -174,7 +161,6 @@ We will have `PC1` send data to `PC2` in the same LAN where the Switch has an em
 * `unknown unicast frame`: frame for which the switch doesn't have an entry in its MAC Address Table. In this case the frame is `FLOODED` (forwarded to all of its interfaces except the one it received the packet on)
 * `known unicast frame`: frame for which destination is already "known" in the switches MAC Address Table. In this case the frame is `FORWARDED` to the specified destination.
 
-
 ### Example 2
 
 `PC1` will send data to `PC3` and `PC3` will reply to `PC1` where the Switch has an empty MAC Address Table
@@ -203,10 +189,10 @@ We will have `PC1` send data to `PC2` in the same LAN where the Switch has an em
 8. `SW1` already associated `PC1` Mac Address to `F0/1` interface so it will `FORWARD` the frame to `PC1` directly
 ![](docs/example_2/8.png)
 
-
 ### Example 3 🔥
 
 `PC1` wants to send data to `PC3` where:
+
 * `PC1` doesn't know `PC3` MAC Address
 * `PC1` knows `PC3` IP address
 
@@ -216,7 +202,7 @@ We will have `PC1` send data to `PC2` in the same LAN where the Switch has an em
 2. `SW1` adds `PC1` to its MAC Address table and `FLOODS` the request
 ![](docs/example_3/2.png)
 
-3. `PC2` ignores the request because Destination IP doesn't match 
+3. `PC2` ignores the request because Destination IP doesn't match
 ![](docs/example_3/3.png)
 
 4. `SW2` adds `PC1` to its MAC Address table and `FLOODS` the request

contents/interfaces_and_cables/README.md

@@ -1,7 +1,7 @@
 # Interfaces and Cables
 
-
 ## Table of contents
+
 * [Network Protocols](#network-protocols)
 * [Bits and Bytes](#bits-and-bytes)
 * [Ethernet](#ethernet)
@@ -12,7 +12,6 @@
 * [Fiber-optic Cable standards](#fiber-optic-cable-standards)
 * [UTP vs Fiber-optic Cabling](#utp-vs-fiber-optic-cabling)
 
-
 ## Network Protocols
 
 Agreed upon system of communicating between network devices.
@@ -59,7 +58,7 @@ Type of copper **cables** used in ethernet standards.
 
 #### Straight-through cable connections
 
-```
+```log
 1 --- 1
 2 --- 2
 
@@ -71,7 +70,7 @@ Type of copper **cables** used in ethernet standards.
 
 #### Crossover cable connections
 
-```
+```log
 1 --- 3
 2 --- 6
 
@@ -82,16 +81,16 @@ Type of copper **cables** used in ethernet standards.
 ![](docs/crossover_router_and_router.png)
 
 #### **Auto MDI-X** 🔥
+
 Truth is that most modern network devices don't need to worry about straight-through or crossover cables because of Auto MDI-X.
 
 It allows deviced to automatically detect which pins their neighbor is transmiting data on, and then adjust which pins to use to transmit/receive data.
 
-
 ### 1000BASE-T and 10GBASE-T
 
 In addition to using **ALL** pairs of wires, each pair is `BI-DIRECTIONAL`. This is part of the reason why they can operate at much faster speeds.
 
-```
+```log
 1 --- 1
 2 --- 2
 
@@ -114,6 +113,7 @@ In addition to using **ALL** pairs of wires, each pair is `BI-DIRECTIONAL`. This
 ![](docs/fiber_cable.png)
 
 ![](docs/fiber_optic_layers.png)
+
 * `1` : Fiber glass core, where light is transmitted
 * `2` : Cladding that reflects light
 * `3` : Protective buffer
@@ -139,8 +139,8 @@ In addition to using **ALL** pairs of wires, each pair is `BI-DIRECTIONAL`. This
 ![](docs/multimode_fiber.png)
 
 ## Fiber-optic Cable standards
-![](docs/fiber_optic_standards.png)
 
+![](docs/fiber_optic_standards.png)
 
 ## UTP vs Fiber-optic Cabling
 
@@ -151,4 +151,3 @@ In addition to using **ALL** pairs of wires, each pair is `BI-DIRECTIONAL`. This
 | Vulnerable to EMI | EMI proof |
 | RJ45 ports are cheaper than SFP ports | SFP ports are more expensive (and single-mode ir more expensive than multimode) |
 | Leak faint signal outside of cable (security risk) | No signal leak |
-