GRE Multilink Simlet

Refer to the topology below and answer the following questions.

Note: There may be different faults in this sim so please notice the following faults:

1. ACL blocking traffic on interface between R2 and R3
2. The network was not advertised in EIGRP
3. Two routers couldn’t establish adjacency because of ACL
4. Another two routers couldn’t establish adjacency because of wrong IP configuration on interface between them

Question 1

Why is the Branch2 network 10.10.20.0/24 unable to communicate with the Server farm 1 network 10.10.10.0/24 over the GRE tunnel?
A. The GRE tunnel destination is not configured on the R2 router.
B. The GRE tunnel destination is not configured on the Branch2 router.
C. The static route points to the tunnel0 interface that is misconfigured on the Branch2 router.
D. The static route points to the tunnel0 interface that is misconfigured on the R2 router.

Answer: C

The Branch2 network is communicating to the Server farm, which is connected to R2, via GRE Tunnel so we should check the GRE tunnel first to see if it is in “up/up” state with the “show ip interface brief” command on the two routers.

On Branch2:

Branch2#show ip interface brief
Interface IP-Address OK? Method Status Protocol
Ethernet0/0 10.10.20.1 YES manual up up
Ethernet0/1 192.168.11.1 YES manual up up
Ethernet0/2 unassigned YES unset administratively down down
Ethernet0/3 unassigned YES unset administratively down down
Serial1/0 192.168.15.2 YES manual up up
Serial1/1 unassigned YES unset administratively down down
Serial1/2 unassigned YES unset administratively down down
Serial1/3 unassigned YES unset administratively down down
Tunnel0 192.168.24.2 YES manual up up

On R2:

R2#show ip interface brief
Interface IP-Address OK? Method Status Protocol
Ethernet0/0 172.16.10.2 YES manual up up
Ethernet0/1 10.10.10.1 YES manual up up
Ethernet0/2 192.168.18.1 YES manual up up
Ethernet0/3 unassigned YES unset administratively down down
Tunnel0 192.168.24.1 YES manual up up

We see interfaces Tunnel0 at two ends are “up/up” which are good so we should check for the routing part on two routers with the “show running-config” command and pay attention to the static routing of each router. On Branch2 we see:

Branch2#show running-config
Building configuration…
<omitted output>
ip route 10.10.10.0 255.255.255.0 192.168.24.10
!

<omitted output>

The destination IP address for this static route is not correct. It should be 192.168.24.1 (Tunnel0’s IP address of R2), not 192.168.24.10 -> Answer C is correct.

Note: You can use the “show ip route” command to check the routing configuration on each router but if the destination is not reachable (for example: we configure “ip route 10.10.10.0 255.255.255.0 192.168.24.10” on Branch2, but if 192.168.24.10 is unknown then Branch2 router will not display this routing entry in its routing table.

Note: The IP address or configuration may be different in the exam.

Question 2

Why has the Branch3 router lost connectivity with R1? Use only show commands to troubleshoot because usage of the debug command is restricted on the Branch3 and R1 routers?
A. A PPP chap hostname mismatch is noticed between Branch3 and R1.
B. A PPP chap password mismatch is noticed between Branch3 and R1.
C. PPP encapsulation is not configured on Branch3.
D. The PPP chap hostname and PPP chap password commands are missing on the Branch3 router.

Answer: A

First we should check Branch3 (and R1) with the “show ip interface brief” command to find any Layer1/Layer 2 issue.

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