CCNA FAQ: Route Summarization
Q1. Which of the following summarized subnets is the smallest (smallest range of addresses) summary route that includes subnets 10.3.95.0, 10.3.96.0, and 10.3.97.0, mask 255.255.255.0?
a. 10.0.0.0 255.0.0.0
b. 10.3.0.0 255.255.0.0
c. 10.3.64.0 255.255.192.0
d. 10.3.64.0 255.255.224.0
Explanation: C. All the listed answers include the range of all three subnets, except for 10.3.64.0 255.255.224.0, which implies an address range of 10.3.64.0 – 10.3.95.255. Of the other three answers, 10.3.64.0 255.255.192.0 is the smallest range (10.3.64.0 – 10.3.127.255). It also happens to be the smallest single summary route that includes all three subnets listed in the question.
Q2. Which of the following summarized subnets is not a valid summary that includes subnets 10.1.55.0, 10.1.56.0, and 10.1.57.0, mask 255.255.255.0? (Choose two answers.)
a. 10.0.0.0 255.0.0.0
b. 10.1.0.0 255.255.0.0
c. 10.1.55.0 255.255.255.0
d. 10.1.48.0 255.255.248.0
e. 10.1.32.0 255.255.224.0
Explanation: C and D. 10.0.0.0 255.0.0.0 implies a range of all addresses that begin with 10, and 10.1.0.0 255.255.0.0 implies a range of all addresses that begin with 10.1, so both these answers include all the address ranges listed in the question. 10.1.32.0 255.255.224.0 implies a range of 10.1.32.0 – 10.1.63.255, which includes all addresses listed in the question. 10.1.55.0 255.255.255.0 implies a range of only 10.1.55.0 – 10.1.55.255, which does not include all addresses. 10.1.48.0 255.255.248.0 implies a range of 10.1.48.0 – 10.1.55.255, which omits two of the subnets listed in the question.
Q3. Which of the following routing protocols support manual route summarization? (Choose three answers.)
Answer: B, C, and D
Q4. Which routing protocol(s) perform(s) autosummarization by default? (Choose three answers.)
Answer: A, B, and C
Q5. An internetwork has a discontiguous network 10.0.0.0, and it is having problems. All routers use RIP-1 with all default configurations. Which of the following answers lists an action that, by itself, would solve the problem and allow the discontiguous network?
a. Migrate all routers to use OSPF, using as many defaults as is possible.
b. Disable autosummarization with the no auto-summary RIP configuration command.
c. Migrate to EIGRP, using as many defaults as is possible.
d. The problem cannot be solved without first making network 10.0.0.0 contiguous.
Explanation: A. Discontiguous networks are allowed as long as autosummarization is disabled. OSPF does not even support autosummarization, so using OSPF would solve the problem. RIP-1 cannot disable autosummarization. EIGRP can disableautosummarization, but it is on by default.