#####   ######  #####    ###    #   #  ###  #   #  ######
##  ##  ##      ##  ##  ## ##   #   #   #   #   #  ##
#####   ####    #####   #   #   #   #   #   #   #  ####
##  #   ##      ##      ## ##    # #    #    # #   ##
##   #  ######  ##       ###      #    ###    #    ######

$ curl repovive.com/roadmaps/network-design/routing-fundamentals/bandwidth-based-metrics

░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░████████████████████████████████████████████████████████████████████████████████████████

#####   ######  #####    ###    #   #  ###  #   #  ######
##  ##  ##      ##  ##  ## ##   #   #   #   #   #  ##
#####   ####    #####   #   #   #   #   #   #   #  ####
##  #   ##      ##      ## ##    # #    #    # #   ##
##   #  ######  ##       ###      #    ###    #    ######

$ curl repovive.com/roadmaps/network-design/routing-fundamentals/bandwidth-based-metrics

Repovive

Bandwidth-Based Metrics - Routing Fundamentals | Network Design | Repovive

Repovive.

Network Design26 sections · 911 units44h total

Open in Course

Bandwidth-Based Metrics

OSPF's approach

OSPF calculates cost based on interface bandwidth. The formula is:

$\text{Cost} = \frac{\text{Reference Bandwidth}}{\text{Interface Bandwidth}}$

The default reference bandwidth is $100$ Mbps ( $10^8$ bps). Examples:

$10$ Mbps link: cost $= 100/10 = 10$
$100$ Mbps link: cost $= 100/100 = 1$
$1$ Gbps link: cost $= 100/1000 = 0.1 \rightarrow 1$ (minimum)

The problem: links faster than $100$ Mbps all get cost $1$ . Modern networks should increase the reference bandwidth:

Router(config-router)# auto-cost reference-bandwidth 10000

This sets reference to $10$ Gbps, allowing differentiation between fast links.