Can't ping

Answered Question
Oct 1st, 2010
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Hello everyone,


Today at school we made our first Cisco exercise in Packet Tracer.

Later on we also made the same exercice with real routers and switches, everything worked.

But today when I got home I tried to remake the exercise with packet tracer and I have a little problem.

If you open the attached .pkt-file you will see 4 computers.

When i try to ping from one of the computers on the left to one on the right, it doesn't work.

It must have something to do with the routers..

I have tried everything but I can't get it to work.

I'm getting kind of crazy here

So could anyone help me out?

For most of the people here I think this is a very easy exercise, so I'm hoping someone could help me out


Thanks!

Correct Answer by Federico Coto F... about 6 years 9 months ago

In summary...


LAN1 --- switch1 --- router1 ---- router2 ----- switch2 ---- LAN2


LAN1=192.168.1.0/24

GW 192.168.1.1 (which is router1)


LAN2=192.168.2.0/24

GW 192.168.2.1 (which is router2)


Everything fine so far?


If a traceroute from LAN1 dies on router1, it tells me that routing is not correct.


On router1 you should have the following:

ip route 192.168.2.0 255.255.255.0 192.168.3.3


On router2 you should have the following:

ip route 192.168.1.0 255.255.255.0 192.168.3.2


The whole idea is this:

PC1 sends a packet intended to PC2

Packet arrives at the switch (since it's a layer 2 switch it does not care about the IPs, it just switches the frame to the router.

Packet arrives at R1.

R1 looks up the routing table and according to the above route it finds that to reach 192.168.2.0/24 (LAN2) it should send the packets to R2.

R2 receives the packet.

R2 knows that LAN2 is directly connected and deliver the packet to the PC (going through switch2).

Same thing happens on the way back.


Federico.

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Federico Coto F... Fri, 10/01/2010 - 11:03
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Hi,


I did open the packet tracer file and see nothing.

I'm using version 5.3


Federico.

vanhessche Fri, 10/01/2010 - 11:50
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That's strange...

I tried downloading it from here and opened it and I can see what I made ...

I'm using 5.3.1.0044.

Federico Coto F... Fri, 10/01/2010 - 11:55
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I'm getting an incompatibility error when trying to open it (weird I'm using version 5.3.0.0088 and don't have yours).

Anyway, do you have something like this:


computer ---- router --- computer


And you're trying to PING between computers? Or are there more devices involved?


Federico.

vanhessche Fri, 10/01/2010 - 12:05
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The situation is like this:


2 computers-----switch-----router------(serial cable)-----router-----switch-----2 computers


on each side, I can ping to the other computer that is on the same switch.

I can also ping the standard gateway IP, and even the IP of the closest router.

but when I try to ping, with one of the left pc's, to the router on the right, it times out.

and when i try to ping to one of the pc's on the other side, the system says that the host in unreachable.

Federico Coto F... Fri, 10/01/2010 - 12:10
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You should verify the following:


The gateway for the PCs on the left should be the IP of the left router (of the interface facing them).

Same applies to the PCs on the right.


You should PING between the routers.


A very nice tool is traceroute that will show you were are the packets dying.


So, from PC on the left do:


traceroute x.x.x.x (where x.x.x.x is the IP of the PC on the right).

This will let you know where does the packet ends and right there is where you're having the problem.


I am assuming that the problem is this:

The left router does not have a route to reach the PCs on the right.

The right router does not have a route to reach the PCs on the left.

Or you have the default gateway on the PCs misconfigured.


Question:

Are you running a routing protocol on the routers or just a static route?


Federico.

vanhessche Fri, 10/01/2010 - 12:29
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I tried the traceroute.

I get to the default gateway and then it stops...

For the pc's on the left this is 192.168.1.1

For the pc's on the right this is 192.168.2.1

The IP's of the routers on the sides where hey are facing eachother are 192.168.3.2 (left) and 192.168.3.3 (right)

The rest seems okay, like you said in the previous post, the IP of the interface facing the pc's on the router is the standard gateway.


So the problem must be the routing.

I run a static rout.

On the left router this is: 192.168.1.0/24 via 192.168.3.3

On the right one this is: 192.168.2.0/24 via 192.168.3.2


I must be forgetting something..

Correct Answer
Federico Coto F... Fri, 10/01/2010 - 12:55
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In summary...


LAN1 --- switch1 --- router1 ---- router2 ----- switch2 ---- LAN2


LAN1=192.168.1.0/24

GW 192.168.1.1 (which is router1)


LAN2=192.168.2.0/24

GW 192.168.2.1 (which is router2)


Everything fine so far?


If a traceroute from LAN1 dies on router1, it tells me that routing is not correct.


On router1 you should have the following:

ip route 192.168.2.0 255.255.255.0 192.168.3.3


On router2 you should have the following:

ip route 192.168.1.0 255.255.255.0 192.168.3.2


The whole idea is this:

PC1 sends a packet intended to PC2

Packet arrives at the switch (since it's a layer 2 switch it does not care about the IPs, it just switches the frame to the router.

Packet arrives at R1.

R1 looks up the routing table and according to the above route it finds that to reach 192.168.2.0/24 (LAN2) it should send the packets to R2.

R2 receives the packet.

R2 knows that LAN2 is directly connected and deliver the packet to the PC (going through switch2).

Same thing happens on the way back.


Federico.

vanhessche Fri, 10/01/2010 - 13:06
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Allright!

It works

I just got the routing idea wrong

Thank you very much!

Federico Coto F... Fri, 10/01/2010 - 13:08
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Glad I could help :-)

And thanks for the rating.


Federico.

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