CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
R1# show ip bgp neighbors 10.1.1.2 received-routes
BGP table version is 5, local router ID is 192.168.0.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 10.10.0.0/16 10.1.1.2 0 0 65001 65002 i
*> 10.20.0.0/16 10.1.1.2 0 0 65001 65003 65004 i
*> 10.30.0.0/16 10.1.1.2 0 0 65001 i
R1# show ip route 10.30.0.0
Routing entry for 10.30.0.0/16
Known via "bgp", distance 20, metric 0
Tag 65001, type external
Last update from 10.1.1.2 00:00:12 ago
Routing Descriptor Blocks:
* 10.1.1.2, from 10.1.1.2, 00:00:12 ago
Route metric is 0, traffic share count is 1
AS Hops 1
Route tag 65001
MPLS label: none
Refer to the exhibit. Which of the following is true regarding the BGP routes received from neighbor 10.1.1.2?
R1# show ip bgp neighbors 10.1.1.2 received-routes
BGP table version is 5, local router ID is 192.168.0.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 10.10.0.0/16 10.1.1.2 0 0 65001 65002 i
*> 10.20.0.0/16 10.1.1.2 0 0 65001 65003 65004 i
*> 10.30.0.0/16 10.1.1.2 0 0 65001 i
R1# show ip route 10.30.0.0
Routing entry for 10.30.0.0/16
Known via "bgp", distance 20, metric 0
Tag 65001, type external
Last update from 10.1.1.2 00:00:12 ago
Routing Descriptor Blocks:
* 10.1.1.2, from 10.1.1.2, 00:00:12 ago
Route metric is 0, traffic share count is 1
AS Hops 1
Route tag 65001
MPLS label: none
A
The route to 10.30.0.0/16 is filtered out by an inbound route-map.
Why wrong: Incorrect. The route is present in the received routes and also appears in the routing table, so it is not filtered.
B
The route to 10.20.0.0/16 is preferred over 10.10.0.0/16 due to shorter AS path.
Why wrong: Incorrect. The AS path for 10.20.0.0/16 is 65001 65003 65004 (3 ASes) while 10.10.0.0/16 has AS path 65001 65002 (2 ASes). The route with shorter AS path (10.10.0.0/16) would be preferred, but they are different networks.
C
All three routes are installed in the routing table.
Correct. The '>' symbol next to each route indicates they are the best paths and thus installed in the routing table.
D
The route to 10.30.0.0/16 has a local preference of 100.
Why wrong: Incorrect. The output does not show a local preference value; it is blank (default 100). However, there is no explicit indication that it is set to 100.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
All three routes are installed in the routing table.
The received routes include 10.10.0.0/16, 10.20.0.0/16, and 10.30.0.0/16. The route to 10.30.0.0/16 is originated from AS 65001 (AS path shows only 65001). The other routes have longer AS paths. The '>' symbol indicates the best path. All received routes are marked as best, meaning they are all installed in the routing table. The route to 10.30.0.0/16 has only one AS hop, so it is directly from AS 65001.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The route to 10.30.0.0/16 is filtered out by an inbound route-map.
Why it's wrong here
Incorrect. The route is present in the received routes and also appears in the routing table, so it is not filtered.
✗
The route to 10.20.0.0/16 is preferred over 10.10.0.0/16 due to shorter AS path.
Why it's wrong here
Incorrect. The AS path for 10.20.0.0/16 is 65001 65003 65004 (3 ASes) while 10.10.0.0/16 has AS path 65001 65002 (2 ASes). The route with shorter AS path (10.10.0.0/16) would be preferred, but they are different networks.
✓
All three routes are installed in the routing table.
Why this is correct
Correct. The '>' symbol next to each route indicates they are the best paths and thus installed in the routing table.
The route to 10.30.0.0/16 has a local preference of 100.
Why it's wrong here
Incorrect. The output does not show a local preference value; it is blank (default 100). However, there is no explicit indication that it is set to 100.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Command / output trap
Incorrect. The output does not show a local preference value; it is blank (default 100). However, there is no explicit indication that it is set to 100.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related CISSP OSPF questions on adjacency and route selection.
Communication and Network Security — This question tests Communication and Network Security — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: All three routes are installed in the routing table. — The received routes include 10.10.0.0/16, 10.20.0.0/16, and 10.30.0.0/16. The route to 10.30.0.0/16 is originated from AS 65001 (AS path shows only 65001). The other routes have longer AS paths. The '>' symbol indicates the best path. All received routes are marked as best, meaning they are all installed in the routing table. The route to 10.30.0.0/16 has only one AS hop, so it is directly from AS 65001.
What should I do if I get this CISSP question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related CISSP OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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