Discovering computer networks: hands on in the Open Networking Lab
Discovering computer networks: hands on in the Open Networking Lab

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Discovering computer networks: hands on in the Open Networking Lab

14.2 Routing with default static routes

In this section you will to take a more detailed look at static routes.

Watch the video below, which is just under 2 minutes long.

Routing with default routes 1

Download this video clip.Video player: 76_routing_with_default_routes.mp4
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Transcript

The reason why the pings previously failed was because there was no route in the routing table for the destination network.

One solution to the problem would be to put in a default static route – which we briefly saw in a previous session

To do this we are going to add the command ip route 0.0.0.0 0.0.0.0 10.10.10.2 to Router1. This is called the quad zero route (as it matches all destination networks to the specified IP address). In this case, all traffic for unknown networks will be forwarded to the IP address of gigabit 0/0 on Router2 – this will result in all traffic to unknown networks being sent to Router2.

We will now ping 10.10.10.2 from PC1 again.

This ping still fails.

We will now introduce another useful diagnostic command called traceroute, which is used in network fault-finding to see where the path to a destination network fails.

On a Windows PC this command is entered at a command prompt by typing tracert. We can see from the results that there is still no completed path from R1 to R2 – yet we have already entered a default static route out of R1 to R2, which can be demonstrated by using the show ip routecommand on Router1. It shows up as ‘Gateway of last resort is 10.10.10.2 to network 0.0.0.0’. The default static route also shows up at the end of the routing table with an S* next to it.

We need to think about why this might be happening.

End transcript
 
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Activity 2 Think about

5 minutes

An extract from the routing table of Router 2 from the demonstration network in the first video is shown below.

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C 10.10.10.0/24 is directly connected, GigabitEthernet0/0 L 10.10.10.2/32 is directly connected, GigabitEthernet0/0 172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks C 172.16.1.0/24 is directly connected, GigabitEthernet0/1 L 172.16.1.1/32 is directly connected, GigabitEthernet0/1

Following the additional configuration to Router 1 shown in the second video, PC1 still cannot ping PC3. Can you think of any reason why this might be happening? Choose the best answer from the options below.

a. 

The default route from Router 1 to Router 2 is incorrectly configured.


b. 

There is no reverse path in Router 2’s routing table to direct the returning traffic back to Router 1.


c. 

PC3 has been configured with an incorrect IP address.


d. 

The ping typed on PC1 had the wrong IP address.


The correct answer is b.

b. 

Yes. In Router 2’s routing table, there is no known route from Router 2 to Router 1 for packets addressed to anything in the 192.168.1.0/24 network.


OPNL_1

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