ajout Static Route

11. Static Routing.md

@@ -2,10 +2,13 @@
 id: 1777544578-NSAK
 aliases:
   - Static Routing
-tags: []
+tags:
+  - CCNA
+  - Router
 ---
 
 # Static Routing
+
 ## Network diagram
 
 ![Diagram](./Images/Diagram_Static_routing.png)
@@ -15,10 +18,219 @@ tags: []
 End hists like PC1 and PC4 can send packets directly to destinations in their connected network.
 - PC1 is connected to 192.168.1.0/24, PC4 is connected to 192.168.4.0/24
 
+To send packets to destinations outside of their local network, they must send the packets to their default gateway.
+
+```PC1 (linux Config)
+iface eth0 inet static
+  address 192.168.1.10/24
+  gateway 192.168.1.1
+```
+
+```PC4 (linux Config)
+iface eth0 inet static
+  address 192.168.4.10/24
+  gateway 192.168.4.4
+```
+
+The default gateway configuration is also called a default route.
+- It is a route to 0.0.0.0/0 = all netmask bits set to 0. Includes all addresses 0.0.0.0 -> 255.255.255.255
+
+      The default route is the least specific route possible, because it includes all [[IP addresses]].
+      0.0.0.0 = 4,294,967,296 IP addresses
+      A /32 route (ie. Local route) is the most specific route possible, because it specifies only one IP address
+      192.168.1.1/32 = 1 IP address
+
+End hosts usually have no need for any more specific routes.
+
+- They just need to know: to send packets outside of my local network, I should send them to my default gateway
+  - Src. IP: 192.168.1.10
+  - Dst. IP: 192.168.4.10
+  - Dst. MAC = R1 G0/2 MAC
+  - Src. MAC = PC1 eth0 MAC
+    - to learn R1 G0/2's MAC address, PC1 will first send an [[ARP]] request to 192.168.1.1
+    
+- When R1 Receives the frame from PC1, it will de-encapsulate it (remove L2 header/ trailer) and look at the inside packet.
+
+- It will check the routing table for the most-specific matching route:
+
+- R1 has no matching routes in irs routing table.
+  - It will drop the packet.
+  
+- To properly forward the packet, R1 needs a route to the destination network (192.168.4.0/24)
+  - Routes are instructions: to send a packet to destinations in network 192.168.4.0/24, forward the packet to next hop Y
+  
+- There are two possible path packets from PC1 to PC4 can take:
+   1) PC1 -> R1 -> R3 -> R4 -> PC4
+   2) PC1 -> R1 -> R2 -> R4 -> PC4
+   
+    - (it will be learn later)
+
+## Static Route configuration
+
+Each router in the path needs two routes: a route to 192.168.1.0/24 and a route to 192.168.4.0/24. 
+  - this ensures two-way reachability (PC1 can send packets to PC4, PC4 can send packets to PC1).
+  
+        routers don't need routes to all networks in the path to the destination.
+          - R1 doesn't need a route to 192.168.34.0/24.
+          - R4 doesn't need a route to 192.168.13.0/24.
+          
+- R1 already has a **Connected route** to 192.168.1.0/24
+- R4 already has a **Connected route** to 192.168.4.0/24
+  - The other routes must be manually configured (using **Static Routes**)
+
+### Static Route Chart
+  
+  | Router | Destination    | Next-Hop       |
+  | ------ | -------------- | -------------- |
+  |   R1   | 192.168.1.0/24 | Connected      |
+  |   R1   | 192.168.4.0/24 | 192.168.13.3   |
+  |   R3   | 192.168.1.0/24 | 192.168.13.1   |
+  |   R3   | 192.168.4.0/24 | 192.168.34.4   |
+  |   R4   | 192.168.1.0/24 | 192.168.34.3   |
+  |   R4   | 192.168.4.0/24 | Connected      |
+
+
+### R1 Configuration
+
+For configuring Static route the command is:
+
+ ```Cisco 
+R1(config)# ip route ip-address netmask next-hop
+```
+
+so for R1:
+
+ ```Cisco 
+R1(config)# ip route 192.168.4.0 255.255.255.0 192.168.13.3
+```
+
+To check the routes
+
+ ```Cisco 
+R1(config)# do show ip route
+
+Codes: L - local, C - connected, S - static ....
+
+//partial return
+
+192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
+C 192.168.1.0/24 is directly connected, GigabitEthernet0/2  
+L 192.168.1.1/32 is directly connected, GigabitEthernet0/2  
+S 192.168.4.0/24 [1/0] via 192.168.13.3 
+```
+
+      The [1/0] displayed in static routes means:
+      [adminstrative Distance/Metric]
+      We will cover these concepts later in the course.
+
+so for R3:
+
+ ```Cisco 
+R3(config)# ip route 192.168.1.0 255.255.255.0 192.168.13.1
+// to send packets to 192.168.1.0/ 24 send packets to R1 
+R3(config)# ip route 192.168.4.0 255.255.255.0 192.168.34.4
+// to send packets to 192.168.4.0/ 24 send packets to R4 
+```
+
+so for R4:
+
+ ```Cisco 
+R4(config)# ip route 192.168.1.0 255.255.255.0 192.168.34.3
+```
+
+### Test connection
+
+Now to see if *PC1* and *PC4* can communicate
+
+
+```powershell
+PC1:$ ping 192.168.4.10
+5 packets transmitted, 5 packets received, 0% packet loss
+```
+
+If the ping is successful, that means there is two-way reachability.
+*PC1* can reach *PC4*, and *PC4* can reach *PC1*
+
+## Static Route Configuration with exit-interface
+
+instead of configuring a next hop we can configure an exit interface
+instead of the ip address we can specify the interface
+
+We will do this for R2:
+
+ ```Cisco 
+R2(config)# ip route ip-address netmask exit-interface
+R2(config)# ip route 192.168.1.0 255.255.255.0 g0/0
+```
+
+but we can do both exit-interface and next-hop
+
+ ```Cisco 
+R2(config)# ip route ip-address netmask exit-interface next-hop
+R2(config)# ip route 192.168.4.0 255.255.255.0 g0/1 192.168.24.4
+```
+
+so it returns
+
+ ```Cisco 
+R2(config)# do show ip route
+
+// exit interface
+S   192.168.1.0/24 is directly connected, GigabitEthernet0/0
+
+// exit interface and next-hop
+S   192.168.4.0/24 [1/0] via 192.168.24.4, GigabitEthernet0/1
+```
+
+- Static routes in which you specify only the exit-interface rely on a feature called Proxy ARP to function
+- This is usually not a problem, but generally you can stick to 
+  - next-hop or exit-interface next-hop
+- Neither is 'better' than the other: use which you prefer.
+
+## Default route
+
+- A default route is a route to 0.0.0.0/0
+  - 0.0.0.0/0 is the least specific route possible; it includes every possible destination IP address.
+- if the router doesn't have any more specific routes that match a packet's destination IP address, the router
+  will forward the packet using the default route.
+- A default route is often used to direct traffic to the [[Internet]].
+
+- Example for a internal corporate network.:
+  - More specific routes are used for destinations in the internal corporate network.
+  - Traffic to destinations outside of the internal network is sent to the internet.
+
+!(default route)[./Images/default_routes.png]
+
+### configure default route
+
+```Cisco
+R1# show ip route
+Gateway of last resort is not set
+```
+
+No default route has been configured yet
+To configure a default route use this command
+
+```Cisco
+R1(config)# ip route 0.0.0.0 0.0.0.0 203.0.113.2
+
+//check
+R1(config)# do show ip route
+* - candidate default
+
+S*  0.0.0.0/0 [1/0] via 203.0.113.2
+```
+
 ## Review
 
 - Connected and Local routes
 [[Routing Fundamentals]]
 - Intro to Static Routes
 - Static Route configuration
+
+```Cisco
+R2(config)# ip route ip-address netmask next-hop
+R2(config)# ip route ip-address netmask exit-interface
+R2(config)# ip route ip-address netmask exit-interface next-hop
+```
 - Default Routes