237 lines
6.8 KiB
Markdown
237 lines
6.8 KiB
Markdown
---
|
|
id: 1777544578-NSAK
|
|
aliases:
|
|
- Static Routing
|
|
tags:
|
|
- CCNA
|
|
- Router
|
|
---
|
|
|
|
# Static Routing
|
|
|
|
## Network diagram
|
|
|
|
|
|
|
|
## 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.
|
|
|
|
!(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
|