---
# System prepended metadata

title: Homework Loopback Interface
tags: [Smallko, homework, loopback, Networking]

---

# Homework Loopback Interface 

###### tags: `Networking` `Smallko` `homework` `loopback`

[TOC]

![](https://i.imgur.com/3pWeutv.png)

## What is loopback 
loopback interface is a logical interface on the router that won't go down unless you shutter the interface down.

So if one of the interface goes down it's not a problem because you can still reach the loopback interface. 

![](https://i.imgur.com/SPVNO9M.png)




## Routing problem 

![](https://i.imgur.com/LbtKqdc.png)
we couldn't ping 2.2.2.2 of right at 2, because it's not advertised in a routing protocol 



### EIGRP
Solve way is to enable [EIGRP](/dFay6GVWSRC37Od6imRRTw) 


![](https://i.imgur.com/OFePBNE.png)


![](https://i.imgur.com/QsX3tv8.png)

![](https://i.imgur.com/YkSPK3k.png)

the neighbor relationship have been establish.


Now router can find the way to reach another router (dynamic routing is my god XD)

![](https://i.imgur.com/8uuAv8n.png)


```
show ip eigrp neighbors
```

![](https://i.imgur.com/Ntuyi7P.png)

![](https://i.imgur.com/QqCerFI.png)



## Ping loopback interface 
![](https://i.imgur.com/1bY5OD7.png)

Now we can ping freely 

---

# A triangle of the static routeing 

![](https://i.imgur.com/grJ1tAr.png)


![](https://i.imgur.com/J6WwZs1.png)

![](https://i.imgur.com/ZjvvJwN.png)

![](https://i.imgur.com/dEMq8Uq.png)

<!-- I thought I need to use script, Otherwise, type those  repeatedly cmds which are annoying. 

I just like a idiot.

In this case, I didn't use static routing, because I have dug how to set one. (I'm slacker :kissing_smiling_eyes: )  -->

## Dynamic Routing  
![](https://i.imgur.com/KvS5SzM.png)

![](https://i.imgur.com/S9rVAFW.png)

![](https://i.imgur.com/M9FGun1.png)


## Static routing 

### Configure static routing 
```
ip route <target ip and subnetmask> <via where router port >
```

Example:![](https://i.imgur.com/mN3SdKy.png)




### Check routing table 

```
show ip route
```
R1-> R2 ,R3
![](https://i.imgur.com/cU5Q41C.png)



R2->R1 ,R3

![](https://i.imgur.com/HrwrfFH.png)
![](https://i.imgur.com/yoRc8Uo.png)


R3-> R1,R2

![](https://i.imgur.com/1t8EdUg.png)
![](https://i.imgur.com/mtD52Zx.png)

## Ping loopback interface 


### Dynamic Routing 
![](https://i.imgur.com/XGIfXBF.png)

![](https://i.imgur.com/j4PJjSK.png)

![](https://i.imgur.com/vIE0ISb.png)

### Static Routing 

![](https://i.imgur.com/AJItWzb.png)

![](https://i.imgur.com/vNR7BPp.png)

![](https://i.imgur.com/XlZYBYw.png)



# A square of the static routing(lookback interface) 


## Topology and Configuration
![](https://i.imgur.com/nJ5VSgt.png)

![](https://i.imgur.com/MPSouak.png)

![](https://i.imgur.com/3sU07GT.png)

![](https://i.imgur.com/rzp5djI.png)

![](https://i.imgur.com/bE4xhJ9.png)

Setting static routing


R1 <-> R2
R1
```
#ip route 2.2.2.2 255.255.255.255 10.1.1.2
```
R2
```
ip route 1.1.1.1 255.255.255.255 10.1.1.1
```

R2<->R3
R2
```
ip route 3.3.3.3 255.255.255.255 10.1.2.2

```
R3
```
ip route 2.2.2.2 255.255.255.255 10.1.2.1
```

R3<->R4
R3
```
ip route 4.4.4.4 255.255.255.255 10.1.3.2
```
R4
```
#ip route 3.3.3.3 255.255.255.255 10.1.3.1
```

R4<->R1

R4
```
ip route 3.3.3.3 255.255.255.255 10.1.3.1

```
R1
```
ip route 4.4.4.4 255.255.255.255 10.1.4.1
```



R1->R2->R3

## Routing problems 

![](https://i.imgur.com/kJEn6Hk.png)

Why R1 couldn't Receive the packet.
The reason is we haven't tell the packet how to go back, he didn't find the way to go home XD






## Cross route static routing 

R1<->R2<->R3

R1
```
ip route 3.3.3.3 255.255.255.255 2.2.2.2
```

R2
```
ip route 1.1.1.1 255.255.255.255 2.2.2.2
```

Ok now, we success, it works, I am a god 

![](https://i.imgur.com/bzDppen.png)

Result 
![](https://i.imgur.com/KbVUu20.png)


R2<->R3<->R4

R2
```
ip route 4.4.4.4 255.255.255.255 3.3.3.3
```

R4
```
ip route 2.2.2.2 255.255.255.255 3.3.3.3
```

Result
![](https://i.imgur.com/On5xBaE.png)

