I’ve been thinking a lot about the process of knowledge validation. One of the things that frustrates me is the process asking obscure questions that depend on memorization of pointless trivia. This may occur either in the vendor testing or the interview process. On the other hand, I believe that relevant questions should test the appropriate depth of technical knowledge.
The CCNP Route exam covers multi-area OSPF in section 2.0 of the blueprint. If I were concerned that an interviewee had used dumps to pass this exam, I might validate their knowledge myself. One of the cool things about asking technical questions in the interview process is that the interviewer can see how the person being interviewed works their way through the challenge. It also gives the interviewer the opportunity to ask the interviewee to share their level of expertise prior to validating it.
Specific to OSPF, I might offer the following challenge–
R1#show ip int br Interface IP-Address OK? Method Status Protocol FastEthernet0/0 192.168.1.1 YES manual up up FastEthernet0/1 unassigned YES unset administratively down down R1#show run | sec ospf|route router ospf 1 log-adjacency-changes network 192.168.1.0 0.0.0.255 area 256
R2#show ip int br Interface IP-Address OK? Method Status Protocol FastEthernet0/0 192.168.1.2 YES manual up up FastEthernet0/1 unassigned YES unset administratively down down Loopback1 22.214.171.124 YES manual up up R2#show run | sec ospf|route router ospf 10 network 192.168.1.2 0.0.0.0 area 0.0.1.0
Based on the above configuration–
- Will an adjacency be formed between R1 and R2?
- If no, what could be done to allow an adjacency to form?
- If yes, what OSPF routes might be found in R1’s routing table?
- Typing, show ip ospf on R2 would reveal what as the router ID?
Watching someone work through this can tell a lot about their grasp on concepts and the experience they’ve had with this technology. Let’s first review what the correct answers are.
- Will an adjacency be formed between R1 and R2? YES
If no, what could be done to allow an adjacency to form?
- If yes, what OSPF routes might be found in R1’s routing table? No OSPF Routes
- Typing, show ip ospf on R2 would reveal what as the router ID? The OSPF Router ID should be 126.96.36.199
There are a lot of ways that a candidate could go astray with this example. For example, some may get hung up on the fact that there is no area zero. While an area zero is typically required in multi-area OSPF, the lack thereof will not prevent and adjacency from forming. It also will not prevent intra-area routes from being exchanged. Candidates may also mistakenly assume that the OSPF process-id must match. Unlike OSPF, EIGRP uses a concept of autonomous system number and requires it to match between peers.
Another caveat is that everyone knows the area-id must match. At first glance, it seems that there is a mismatch that could prevent an adjacency. R1 has an area-id of 256 and R2 has an area-id of 0.0.1.0. The area-id is a 32 bit number. If we translate R1’s area-id to binary, we see that it is 00000000.00000000.00000001.00000000. If we convert 0.0.1.0 that we see on R2, it is apparent that the area-id is actually consistent between the neighbors.
If the candidate is still with me, I can see if he or she actually catches the fact that the only OSPF enabled interfaces are directly connected with one another. Since the routes are already in the routing table as connected, there will be no OSPF routes.
The final question is fairly straightforward and simply assesses the understanding of how OSPF does its router-id selection. Those who have a solid understanding know that this ID is selected when the process is started and ID’s are prioritized in the following order: 1) hard-coded router-id, 2) highest IP address of active loopback interface, 3) highest IP address of any active non-loopback interface.
Establishing technical assessment scenarios for use in the interview process can be a time consuming process. However, it is important to validate that candidates are as well qualified as they (and their credentials) say they are. Obviously, scenarios should be well-tailored to the position being filled. It is also important to observe the process in which the candidate determines the answers. If this is a conversational process, it can often make sense to ask how they arrived at the answers.