CCNA R&S Question of the Week: Calculate OSPF Cost

Which parameter or parameters are used to calculate OSPF cost on a Cisco IOS routers?

A. Bandwidth
B. Bandwidth and Delay
C. Bandwidth, Delay and MTU
D. Bandwidth, MTU, Reliability, Delay and Load

Reveal Answer

Answer: A.

Nowhere in the RFC for OSPF does it define how to calculate cost, just that there is a cost on every interface. If you add up all the costs and cheapest cost wins for best path. Many moons ago it was decided to automate the process and use an auto cost bandwidth reference (a constant) divided by the bandwidth.  The default on Cisco IOS routers is 100,000,000 (100 meg) divided by the bandwidth.  The lowest possible value is 1, therefore any link speed of 100Megabits per second or fast will have the cost of 1.

 

Related Resources
Cisco White Papers

Related Course
CCNAX v2.0 — CCNA Routing and Switching Boot Camp
ICND1 v2.0 — Interconnecting Cisco Networking Devices, Part 1
ICND2 v2.0 — Interconnecting Cisco Networking Devices, Part 2

CCNA R&S Question of the Week Series

• CCNA R&S Question of the Week: Full-Duplex Ethernet Network
• CCNA R&S Question of the Week: OSI Model Layer
• CCNA R&S Question of the Week: Connection-Oriented Service
• CCNA R&S Question of the Week: No Acknowledgment of Receipt
• CCNA R&S Question of the Week: Switch vs. Hub
• CCNA R&S Question of the Week: Rapid STP States
• CCNA R&S Question of the Week: Rapid STP
• CCNA R&S Question of the Week: Secure Virtual Terminal Sessions
• CCNA R&S Question of the Week: Calculate OSPF Cost

from
CERTIVIEW