[c-nsp] Load Balancing of Unequal Ethernet Bandwidth

[Andy Saykao]

Hi Tony,

Thanks for that.

Yeah I saw at an example of that at:

http://blog.ioshints.info/2007/02/unequal-load-split-with-static-routes.
html

It's a nice trick to know. Although when one link goes down, I believe
you'll lose packets (or they may be delayed or resent) as the
load-sharing algorithm uses round-robin to distribute the load and
doesn't take into account whether the link has gone down or not.

Cheers.

Andy 

-----Original Message-----
From: Tony [mailto:td_miles at yahoo.com] 
Sent: Monday, 16 February 2009 6:02 PM
To: Andy Saykao
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Load Balancing of Unequal Ethernet Bandwidth


Hi Andy,

What do you run as IGP then so that we can help you out ?

If static routes, then you can do it using by having multiple routes
that are to the same destination.

eg. on 2x serial links you might have:

serial1 = 200Mbps (10.1.1.1/30)
serial2 = 100Mbps (10.1.1.5/3)

You would then add static routes like this:
 ip route x y serial1
 ip route x y 10.1.1.2
 ip route x y serial2 

This way when you do "show ip route x" you would see something like:

* directly connected via serial1
      Route metric is 0, traffic share count is 1
* directly connected via serial2
      Route metric is 0, traffic share count is 1
*  10.1.1.2
      Route metric is 0, traffic share count is 1

Your router would then divide the traffic into three with one third
going to each of the destinations configured. The fact that two of those
destinations are the same link means that two thirds will go down your
200Mbps link and one third down your 100Mbps link.

This is fairly basic and doesn't scale very well, but will work.


regards,
Tony.


--- On Mon, 16/2/09, Andy Saykao <andy.saykao at staff.netspace.net.au>
wrote:

> From: Andy Saykao <andy.saykao at staff.netspace.net.au>
> Subject: Re: [c-nsp] Load Balancing of Unequal Ethernet Bandwidth
> To: "Ben Steele" <illcritikz at gmail.com>
> Cc: cisco-nsp at puck.nether.net
> Date: Monday, 16 February, 2009, 5:39 PM Hi Ben,
>  
> When I googled around, there were many discussions abvout using the 
> variance command with eigrp but we don't run eigrp internally as our 
> IGP.
>  
> This is a typical setup where we need to upgrade some of our links, so

> we might upgrade 50M on the second leg and end up with a situation 
> where the first leg is100M and the second leg is 150M. As you may 
> know, some providers aren't so flexible so you can't just upgrade 25M 
> on each leg because they increment by 50M per leg only. Hence my 
> question if it was possible to load balance across unequal ethernet 
> circuits without buying additional bandwidth for both circuits.
>  
> Thanks.
>  
> Andy
> 
>  
> ________________________________
> 
> From: Ben Steele [mailto:illcritikz at gmail.com]
> Sent: Monday, 16 February 2009 5:29 PM
> To: Andy Saykao
> Subject: Re: [c-nsp] Load Balancing of Unequal Ethernet Bandwidth
> 
> 
> You could do this with variance in eigrp, just add variance
> 2 into the
> eigrp config and it will load balance on a 2:1 ratio, if
> your links are
> equally matched in terms of latency you can look at
> enabling per-packet
> load sharing on the 2 egress interfaces to get an even more
> granular
> distribution, this can wreck some havoc with unequal paths
> and out of
> sequence packets though, however if equally similar in
> characteristics
> then performance is usually very good. 
> 
> Ben
> 
> 
> On Mon, Feb 16, 2009 at 4:01 PM, Andy Saykao
> <andy.saykao at staff.netspace.net.au> wrote:
> 
> 
> 	 Is it possible to aggregate and then load balance unequal
> ethernet
> 	circuits like so:
> 	
> 	I have two ethenet circuits on my Cisco router. Both have
> equal
> costs to
> 	the next hop.
> 	
> 	Ethernet Circuit #1- 200M
> 	Ethernet Circuit #2 - 100M
> 	
> 	Can I aggregate both ethernet circuits so that the total
> amount
> of
> 	bandwidth available to the next hop is is 300M?
> 	Can I then load balance it so both circuits are equally
> utilized?
> 	
> 	For example...
> 	
> 	* If I have 150M of traffic flowing to the next hop then
> the
> router
> 	would spread the load across both links like so:
> 	
> 	100M through Ethernet Circuit #1.
> 	50M through Ethernet Circuit #2.
> 	
> 	* The formula to use for this would be something like:
> 	
> 	Utilization / Total Bandwidth = percentage of utilization
> required per
> 	link
> 	150/300 = 0.5
> 	
> 	0.5 x bandwidth of Ethernet #1 = 0.5 x 200 = 100M
> 	0.5 x bandwidth of Ethernet #1 = 0.5 x 100 = 50M
> 	
> 	* If there was a total of 250M of traffic flowing to the
> next
> hop, and
> 	applying the formula above, the router would work out that
> the
> load
> 	distributed across both ethernet links would be:
> 	
> 	166M through Ethernet Circuit #1.
> 	84M through Ethernet Circuit #2.
> 	
> 	Any ideas???
> 	
> 	Thanks.
> 	
> 	Andy



      


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