Cisco CCNA Packet Tracer Ultimate labs: GRE Tunneling. Answers Part 1

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You need to know GRE for the CCNA exam.

Generic Routing Encapsulation (GRE) is a tunneling protocol developed by Cisco Systems that can encapsulate a wide variety of network layer protocols inside virtual point-to-point links over an Internet Protocol network.


In this lab you need to configure a GRE tunnel.

So in this lab we need to configure a GRE tunnel between customer 1 and customer 2. We’ve been told that we need to configure the customer routers to use DHCP addresses on the Internet interfaces and static IP addresses on the internal interfaces.

So let’s start with customer router 1.
I’ll go to configuration mode and then go on to gigabit 0/0/1

The interface is currently shut. So I’m going no shut at the interface and then I’ll configure an IP address using DHCP.

As you can see an IP address has been allocated via DHCP, an IP address of has been allocated.
I’ll go on to interface gigabit 0/0/0 no shut the interface and configure an IP address of

So show ip interface brief
we can see that both interfaces are up, up.

This is the IP address on the Internet facing interface.
This is the IP address on the inside interface. Internet address was assigned via DHCP. Internal or customer facing interface IP address was configured manually.
That happens because the ISP routers are configured as DHCP servers.

So show ip dhcp binding
we can see that this IP address was allocated to this MAC address.

Now we see a DHCP conflict here and that’s because IP address is part of the DHCP pool all IP addresses in this subnet are but the router has this IP address configured on this interface.

So the ISP doesn’t allocate its own IP address to the client but allocate the next IP address in the pool.
So again, show ip interface brief on the customer router. This IP address was allocated via DHCP and the router can ping the ISP router.

I can do something similar on customer 2.
So customer router 2

show ip interface brief
both interfaces are administratively shut down.

So interface gigabit 0/0/1 no shut ip address dhcp
interface gigabit 0/0/0 and while I was typing that an IP address was allocated via DHCP to the router.

IP address on gigabit 0/0/0 is mask
I’ll no shut that interface

So show ip interface brief
both IP addresses are configured, one dynamically and one statically.

show ip route
shows us the routing table notice a gateway of last resort has been configured and the router also has a default route to its ISP.

So ping
The router can ping its default gateway or ISP router.
Can it ping customer router 1?
So ping Yes it can.

We could do a trace as an example to that address and you can see that the traffic is going via the Internet. In other words traffic is traversing these links to get to customer router 1.

As an example, the second hop is this IP address, third hop is this IP address.
So we have IP connectivity between customer 1 and customer 2.

The next step is to configure a DHCP pool on the customer routers to allocate IP addresses to the PCs in the network.

So on customer router 1
conf t ip dhcp pool
and you could call it as anything and I’m just going to call it PC.

In the exam, follow the instructions.
But here, there is a little bit of leeway. You can decide what you want the pool name to be. Network is going to be this; subnet mask is going to be that.
Default router will be

So show ip dhcp binding
we don’t have any bindings yet.

Let’s look at the PC. So on its configuration; we need to configure it to use DHCP.

Go to desktop, command prompt
notice it has an IP address of ping
PC can ping customer router 1.

And on the customer router, we can see again that there was an address conflict. So the router allocated rather than to the client.

You could create an exclusion range for your pool if you want to make sure that a separate range of addresses are used for the client PCs.

We need to do something similar on customer router 2

so conf t ip dhcp pool pc
network with the mask /24 mask, default router will be

  • David Bombal