[c-nsp] Load Balancing of Unequal Ethernet Bandwidth

[Andy Saykao]

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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