3.1 Interpret the components of routing table.
Objective 3.1 sits in IP Connectivity, which carries 25% of the CCNA exam. The questions below are original, written from the official objective title above, and each explanation cites the Cisco page it rests on.
Objective title verbatim from the official objectives. Cisco exam page ↗
A worked example
Shown solved, with the whole explanation open: this is what every question here carries.
A router displays part of its IPv4 routing table.
10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
O 10.10.4.0/24 [110/65] via 10.1.1.2, 00:14:22, GigabitEthernet1/0/1
D 10.10.8.0/24 [90/30720] via 10.1.1.6, 01:02:41, GigabitEthernet1/0/2
S 10.20.0.0/16 [1/0] via 10.1.1.10What does the first value inside each pair of brackets represent?
The concept
Every entry in an IPv4 routing table carries two ranking numbers in brackets. The first ranks how far the router trusts whichever process supplied the entry, and the second ranks paths within that one process.
Why this answer
These three entries come from three different sources. OSPF supplies 110, internal EIGRP supplies 90, and a manually entered route supplies 1. Those leading values are the default trust ranking assigned to each source, which is what the router compares before installing anything.
- AA process identifier such as the 1 in router ospf 1 is local to the device and never appears in the routing table output at all.
- Correct. The leading bracket value is the administrative distance.
- CThe metric is the second bracket value, which is why 65 and 30720 sit beside 110 and 90 rather than replacing them.
- DHop count is the metric one protocol uses, RIP, and it appears in the second field of a RIP entry rather than the first.
Now you: objective 3.1 questions
No account needed. The explanation opens when you answer.
Sample question 1 of 3
Three routing processes each offered a path covering 172.16.8.10, and the table holds all three.
172.16.0.0/16 is variably subnetted, 3 subnets, 3 masks
D 172.16.8.0/26 [90/3072] via 10.0.0.1, GigabitEthernet1/0/1
R 172.16.8.0/24 [120/3] via 10.0.0.5, GigabitEthernet1/0/2
O 172.16.0.0/16 [110/85] via 10.0.0.9, GigabitEthernet1/0/3Why did none of them displace the others?
Sample question 2 of 3
A colleague reads these two lines and concludes the EIGRP path is far worse than the OSPF path.
D 10.30.0.0/16 [90/2172416] via 10.0.0.1, GigabitEthernet1/0/1
O 10.40.0.0/16 [110/12] via 10.0.0.5, GigabitEthernet1/0/2What is wrong with that reading?
Sample question 3 of 3
A prefix sits in the table from EIGRP while OSPF and RIP also hold paths to it. The EIGRP path then fails. How is the entry refilled?
That’s 3 of the full CCNA bank.
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Continue practicingRead the sources
These are the official pages the questions above cite. Reading them is studying the objective from the primary source, which is what the explanations point you toward anyway.