Add "Routing fundamentals" notes

laaraujo · May 13, 2024 · c3584fe · c3584fe
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diff --git a/README.md b/README.md
@@ -13,6 +13,7 @@ Personal notes for learning [CCNA](https://www.cisco.com/site/us/en/learn/traini
 * [Switch Interfaces](./contents/switch_interfaces/)
 * Routing
     * [IPv4 Header](./contents/ipv4_header/)
+    * [Fundamentals](./contents/routing_fundamentals/)
 
 ## Network node icons
 

diff --git a/contents/routing_fundamentals/README.md b/contents/routing_fundamentals/README.md
@@ -0,0 +1,69 @@
+# Routing Fundamentals
+
+Routing is the process that routesrs use to determine the path that IP packets should take over a network to reach their destination.
+Routers store routes to all of their known destinations in a routing table.
+When routers receibe packets, they look in the routing table to find the best route to forward that packet.
+
+## Routing Methods
+
+There are two main routing methods:
+
+* **Dynamic Routing**: routers use dynamic routing protocols (i.e. OSPF) to share routing information with each other automatically and build their routing tables.
+
+* **Static Routing**: a network engineer/admin manually configures routes on the router
+
+## Route
+
+A route tells the router to:
+
+* send a packet to destination X, you should send the package to next-hop Y
+    * `next-hop` = the next router in the path to the destination
+* send the packet directly to the destination (if it is directly connected to the router)
+* receive the packet for yourself (if the destination is the router's own IP address)
+
+## Routing Tables
+
+![Topology of the network used throughout these notes](docs/network_topography.png)
+
+### Pre-config
+
+For simplicity we'll only show R1's config.
+![Configuring router R1's interfaces](docs/pre_config.png)
+
+### Connected and Local routes
+
+* `show ip route` to view routing table 🔥
+
+![`show ip route` command in action](docs/show_ip_route.png)
+
+![Routing table's local and connected IPs (automatically added)](docs/connected_and_local_ips.png)
+
+#### Connected Routes
+
+* Route to the network the interface is connected to
+* **R1 G0/2 IP** = `192.168.1.1/24`
+* Network address = `192.168.1.0/24`
+* It provides a route to all hosts in that network (i.e. *192.168.1.10*, *192.168.1.232*, etc)
+* R1 knows: "if I need to send a packet to any host in 192.168.1.0/24, I should send it out to `G0/2`"
+
+#### Local Routes
+
+* Route to the exact IP address configured in the interface
+* `/32` netmask is used to specify the exact IP address of the interface
+* Even tough R1's G0/2 is configured as `192.168.1.1/24`, the local route is `192.168.1.1/32`
+* R1 knows: "if I receive a package destined for this IP address, the message is for me"
+
+## Route Selection
+
+![R1 wants to send a packet with Destination IP to itself (192.168.1.1)](docs/route_selection_2.png)
+
+![Both local and connected IP addresses match the packet destination](docs/route_selection_1.png)
+
+A packet destined for 192.168.1.1 is matched by 2 routes in the example above:
+
+* `192.168.1.0/24`
+* `192.168.1.1/32`
+
+It will choose the **most specific** matching route.
+
+* **most specific** matching route = the matching route with the longest prefix length 🔥
diff --git a/contents/routing_fundamentals/docs/connected_and_local_ips.png b/contents/routing_fundamentals/docs/connected_and_local_ips.png
diff --git a/contents/routing_fundamentals/docs/network_topography.png b/contents/routing_fundamentals/docs/network_topography.png
diff --git a/contents/routing_fundamentals/docs/pre_config.png b/contents/routing_fundamentals/docs/pre_config.png
diff --git a/contents/routing_fundamentals/docs/route_selection_1.png b/contents/routing_fundamentals/docs/route_selection_1.png
diff --git a/contents/routing_fundamentals/docs/route_selection_2.png b/contents/routing_fundamentals/docs/route_selection_2.png
diff --git a/contents/routing_fundamentals/docs/show_ip_route.png b/contents/routing_fundamentals/docs/show_ip_route.png