ICND1 Routing Technologies & Protocols 5 — Questions and Answers
Question 1: Which feature prevents routing loops in distance-vector protocols by not advertising a route back out the interface from which it was learned?
- Route poisoning
- Split horizon (Correct answer)
- Hold-down timer
- Triggered updates
Correct answer: Split horizon
Split horizon prevents routing loops by prohibiting a router from advertising a route back on the same interface it was received from.
Question 2: An EIGRP router loses its successor route and there is no feasible successor. What process does EIGRP initiate?
- It immediately uses a static default route
- It marks the route as possibly down and sends Query messages to neighbors (Correct answer)
- It floods an LSU to all routers in the domain
- It increases the hop count to 16 to signal unreachability
Correct answer: It marks the route as possibly down and sends Query messages to neighbors
When no feasible successor exists, EIGRP enters Active state for that route and sends Query messages to all neighbors to find an alternative path.
Question 3: Which command configures a default route on a Cisco router and forwards traffic to next-hop 203.0.113.1?
- ip route 0.0.0.0 0.0.0.0 203.0.113.1 (Correct answer)
- ip route default 203.0.113.1
- ip default-route 0.0.0.0 203.0.113.1
- ip route 255.255.255.255 255.255.255.255 203.0.113.1
Correct answer: ip route 0.0.0.0 0.0.0.0 203.0.113.1
A default static route uses the 0.0.0.0 0.0.0.0 network and mask to match all destinations not found in the routing table.
Question 4: What is the purpose of the OSPF dead interval?
- The time OSPF waits before electing a new DR
- The time after which a neighbor is declared down if no Hello is received (Correct answer)
- The interval between LSA flooding cycles
- The timeout for database exchange between neighbors
Correct answer: The time after which a neighbor is declared down if no Hello is received
If a router does not receive a Hello from a neighbor within the dead interval, it declares that neighbor down and recalculates routes.
Question 5: Which command shows the routing protocol timers and networks configured on a Cisco router?
- show ip route summary
- show ip protocols (Correct answer)
- show ip interface brief
- show run | section router
Correct answer: show ip protocols
The 'show ip protocols' command displays active routing protocols, their timers, networks, and administrative distance.
Question 6: In OSPF, two routers are connected on a point-to-point serial link. Which routers are elected as DR and BDR?
- The router with the higher router-ID becomes DR
- No DR or BDR election occurs on point-to-point links (Correct answer)
- Both routers become DR simultaneously
- The router with OSPF priority 1 becomes DR by default
Correct answer: No DR or BDR election occurs on point-to-point links
DR/BDR elections only occur on broadcast and NBMA multi-access networks; point-to-point links do not use DR/BDR.
Question 7: A network administrator wants to summarize the routes 172.16.0.0/24, 172.16.1.0/24, 172.16.2.0/24, and 172.16.3.0/24 into a single advertisement. What is the correct summary route?
- 172.16.0.0/22 (Correct answer)
- 172.16.0.0/23
- 172.16.0.0/21
- 172.16.0.0/24
Correct answer: 172.16.0.0/22
These four /24 networks share the first 22 bits, so they can be summarized as 172.16.0.0/22.
ICND1 Routing Technologies & Protocols 5
Which feature prevents routing loops in distance-vector protocols by not advertising a route back out the interface from which it was learned?