--- id: 1777544578-NSAK aliases: - Static Routing tags: - CCNA - Router --- # Static Routing ## Network diagram ![Diagram](./Images/Diagram_Static_routing.png) ## Default Gateway 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. ![example](./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