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Re: eigrp variance and traffic-share posted 01/20/2005
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Greetings BBD,

If you have routes in your tables with metrics of 128000, 256000, and
384000 then your variance must be at least '4' to include all routes, as
a value of three would not allow the route with a metric of 384000 to be
included, since it is not less than three times 128000.

That said, let's use a variance of "4" as an example:

128000 (best_path_metric) x 4 (variance) = 512000

512000/128000 = 4
512000/256000 = 2
512000/384000 = 1.333~ (this becomes a 1 as the protocol will round this
number down to the nearest whole integer)

If we configure "traffic-share balanced" what will happen?

The router will send the first four (4) packets via the link with the
metric of 128000
The next two (2) packets via the link with the metric of 256000
The next one (1) packet via the link with the metric of 384000 

Then back to the link with the metric of 128000 for the next four
packets...
And so on. 

This is EIGRP doing exactly what we have asked it to do.

Our other option,"traffic-share min across-interfaces", will only share
traffic between multiple interfaces if their cost is equal to that of
the lowest metric. While this is great for sake of convergence if we
lose our best route, it really does not help us to load balance among
the routes in our current example.

Therefore, if you needed these paths to truly behave as "round-robin" in
nature we need to find another way to make them be seen as equal on the
device in question, through some other means of adjustment. 

Now...
How would you accomplish this?
What method(s?) can be implemented to make these paths appear as being
truly equal??
Are there any other ways we can tweak the number of maximum paths EIGRP
will use, given they are present?

HTH,
~M



  

>>> <wing_lam@xxxxxxxxxxxxxx> 01/20/05 8:23 PM >>>

Hi, group;

If I want to share traffic evenly without regarding the metric, even the
metric not the same, can it be done?

i.e. I have three routes to 192.168.7.0/24, with EIGRP Metric 128000,
256000 &384000, the variance is large enough that all the route is
entered
the route table. But I don't want the path with least metric sends
majority
of traffic. Can I distribute evenly in these three paths? (i.e. round
robin)

Thanks,
BBD




                                                                        
                                                              
                      "Mark Lasarko"                                    
                                                              
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<ccielab@xxxxxxxxxxxxxx>, <hashng@xxxxxxxxx>                            
     
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                      Sent by:                 Subject:  Re: eigrp
variance and traffic-share                                          
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                      Please respond to                                 
                                                              
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Greetings Hashiru,

Variance will help control what routes to include by use of a
multiplier.
Including routes with "A metric less than "n" times the minimum metric
route for that destination."
The variable "n", of course, is what follows the 'variance' command.

Whereas 'traffic-share' will control how traffic is distributed among
known routes when multiple routes to a destination exist, meaning they
are already present in the routing table.

I like to remember 'variance' as kind of internal/before... influencing
what routes we might use.

Whereas 'traffic-share' is more external/after... once we know about
routes, having determined we may use them, how we distribute traffic
among those paths if more than one exists.

That said, they can certainly be used together.

For example:

router eigrp 100
 variance 3
 traffic-share (balanced | min)
 ...

Take a few minutes to check out the options on the traffic-share
command.

Rack1R1(config-router)#variance ?
  <1-128>  Metric variance multiplier

Rack1R1(config-router)#traffic-share ?
  balanced  Share inversely proportional to metric
  min       All traffic shared among min metric paths

Here's a link with a diagram that explains the variance calculation:
http://www.cisco.com/warp/public/103/19.html

HTH,
~M





ontrol how traffic is distributed among routes when there are multiple
routes for the same destination network that have different costs,

he variance command to instruct the router to include routes with a
metric less than n times the minimum metric route for that destination,
where n is the number specified by the variance command

>>> "Idris, Hashiru Aminu" <hashng@xxxxxxxxx> 1/20/2005 2:19:36 PM >>>

i just couldn't get the real difference between the two commands with
regards to EIGRP  below
Variance X
traffic-share .......
can one be used instead of the other? do they work Collaboratively?
because they all seem to be for load ballacing.
please can someone shade some light on this in an illustrative manner
TIA
Hashiru Idris



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