OSPF Reference Bandwidth Calculator
From Internetworkpro
Contents |
[edit] Intro
In today's networks 10G+ is becoming more and more prevalent. OSPF port costs are automatically determined with a formula of <reference bandwith>/<interface bandwidth>. The default reference bandwidth for IOS and JunOS is 100. This means that 100mbit, 1gbit, 10gbit, or higher all gets the same OSPF cost of 1 which is less than optimal and may cause some inappropriate routing decisions.
This is a very quick and dirty script to help me visualize the effects of chaning the reference bandwidth. It is written in python and should run in just about any version of python.
Please let me know if you want more features or any change. Maybe i will work on it some more
nemith 15:15, 18 June 2007 (CDT)
[edit] Usage
Either chmod 755 the script or run as an argument of your python binary.
The script takes one argument, the reference bandwith
[edit] Examples
Costs for the default reference bandwidth of 100
trogdor% python refbw.py 100 Calculating the OSPF cost values for reference bandwidth: 100 Cost at 100Gbps: 1 (less than min) hops @ 24-bit 16777215 hops @ 32-bit 4294967295 Cost at 40Gbps: 1 (less than min) hops @ 24-bit 16777215 hops @ 32-bit 4294967295 Cost at 10Gbps: 1 (less than min) hops @ 24-bit 16777215 hops @ 32-bit 4294967295 Cost at 1Gps: 1 (less than min) hops @ 24-bit 16777215 hops @ 32-bit 4294967295 Cost at 100Mbps: 1 hops @ 24-bit 16777215 hops @ 32-bit 4294967295 Cost at 10Mbps: 10 hops @ 24-bit 1677721 hops @ 32-bit 429496729 Cost at 6.176Mbps: 16 hops @ 24-bit 1036160 hops @ 32-bit 265257180 Cost at 4.632Mbps: 21 hops @ 24-bit 777120 hops @ 32-bit 198942885 Cost at 3.088Mbps: 32 hops @ 24-bit 518080 hops @ 32-bit 132628590 Cost at 1.544Mps: 64 hops @ 24-bit 259040 hops @ 32-bit 66314295 Cost at 768kbps: 133 hops @ 24-bit 125829 hops @ 32-bit 32212254 Cost at 384kbps: 266 hops @ 24-bit 62914 hops @ 32-bit 16106127 Cost at 128kbps: 800 hops @ 24-bit 20971 hops @ 32-bit 5368709
[edit] Code
import sys def calc_cost(refbw, bw): cost = refbw/bw tag = "" if cost < 1: cost = 1 tag = "(less than min)" if cost > 65535: cost = 65535 tag = "(greater than max)" hops_24 = 16777215/cost hops_32 = 4294967295/cost return "%5i %20s hops @ 24-bit %10d hops @ 32-bit %10d" % (cost, tag, hops_24, hops_32) if len(sys.argv) == 1: print 'No reference bandwidth specified!' sys.exit() try: ref_bw = int(sys.argv[1]) except: print "Reference bandwith must be an interger!" sys.exit() print "" print "Calculating the OSPF cost values for reference bandwidth: %i" % ref_bw print "" print "Cost at 100Gbps: %s" % calc_cost(ref_bw, 100000) print "Cost at 40Gbps: %s" % calc_cost(ref_bw, 40000) print "Cost at 10Gbps: %s" % calc_cost(ref_bw, 10000) print "Cost at 1Gps: %s" % calc_cost(ref_bw, 1000) print "Cost at 100Mbps: %s" % calc_cost(ref_bw, 100) print "Cost at 10Mbps: %s" % calc_cost(ref_bw, 10) print "Cost at 6.176Mbps: %s" % calc_cost(ref_bw, 6.176) print "Cost at 4.632Mbps: %s" % calc_cost(ref_bw, 4.632) print "Cost at 3.088Mbps: %s" % calc_cost(ref_bw, 3.088) print "Cost at 1.544Mps: %s" % calc_cost(ref_bw, 1.544) print "Cost at 768kbps: %s" % calc_cost(ref_bw, 0.75) print "Cost at 384kbps: %s" % calc_cost(ref_bw, 0.375) print "Cost at 128kbps: %s" % calc_cost(ref_bw, 0.125)
