GRE Multilink Sim

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

Explanation

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:

On R2:

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:

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

Explanation

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

We see the interfaces connecting between them are in “up/down” states which indicates an Layer 2 issue so we should check the configuration of these interfaces carefully with the “show running-config” command and pay attention to these interfaces.

and on Branch3:

We learn from above config is R1 is using CHAP to authenticate Branch3 router (via the “ppp authentication chap” command on R1). Branch3 router is sending CHAP hostname “Branch_3” and CHAP password “Branch3_Secret!” to R1 to be authenticated. Therefore we should check if R1 has already been configured with such username and password or not with the “show running-config” command on R1:

On R1 we see the configured username is “Branch3”, not “Branch_3” so the usernames here are mismatched and this is the problem -> Answer A is correct.

Question 3

Explanation

In this question we have to check each option to see if it is correct. When we check Branch3 router we notice that “network 192.168.10.0” command is missing under “router eigrp 100” -> Answer D is correct.

Note: In the exam you should check other config as well. There are some reports saying that the answer of this question is different in the exam (answer A).

Question 4

Explanation

This question clearly stated there is a WAN connectivity issue between R1 and Branch1 so we should check both of them with the “show ip interface brief” command. On R1:

On Branch1:

We can see that although the Multilink1 interfaces are in “up/up” state but they are not in the same subnet. According to the IP address scheme shown on the topology we can deduce the Multilink interface on Branch1 has been misconfigured, it should be 192.168.14.2 instead.

Note:

The configs and answers in the exam may be different as a candidate on our site said:

“1- Why did Branch1 router lose WAN connectivity with R1 router?
The answer here was IP misconfigured but in the exam the problem was in multilink group
2 – Which statement about the router configurations is correct?
The answer here was The Branch3 LAW network 192.168.10.0/24 is not advertised into the EIGRP network but in the exam the right was that PPP PAP authentication between them”

So please grasp the concept behind each question well and check all the configuration carefully.