CCNA Exam Prep Question of the Week

You have been assigned the 172.17.8.0/21 address space for your office. You have a few LANs with a maximum of 70 device addresses, and some point-to-point WANs. You use the zero subnet. What is the range of addresses on the third LAN subnet?

  1. 172.17.2.1 to 172.17.2.254
  2. 172.17.9.1 to 172.17.9.126
  3. 172.17.3.1 to 172.17.3.126
  4. 172.17.3.1 to 172.17.3.254
  5. 172.17.9.129 to 172.17.9.254

The correct answer is 2.

For 70 device addresses, 7 host bits are needed so a mask of /25 should be used for the LANs; this means 4 bits of further subnetting for the LANs from the given /21. The third subnet has bits 0010. The address of this subnet is 172.17.00001001.00000000. This is 172.17.9.0; the addresses are 172.17.9.1 through 172.17.9.126

Resources:
CCNA Cert Check
CCNA Exam Prep Mobile App

Related Courses:
ICND1    —    Interconnecting Cisco Network Devices 1
ICND2    —    Interconnecting Cisco Network Devices 2
CCNAX    —    CCNA Boot Camp v1.1

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