[c-nsp] Load Balancing of Unequal Ethernet Bandwidth
Tony
td_miles at yahoo.com
Mon Feb 16 04:03:33 EST 2009
Hi Andy,
What happens when one link goes down depends on a few variables. In the simplest case it works as you would expect. Eg:
ip route 0.0.0.0 0.0.0.0 ATM0.1 5
ip route 0.0.0.0 0.0.0.0 Tunnel0 5
router#show ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
Known via "static", distance 5, metric 0 (connected), candidate default path
Routing Descriptor Blocks:
* directly connected, via ATM0.1
Route metric is 0, traffic share count is 1
directly connected, via Tunnel0
Route metric is 0, traffic share count is 1
router#conf t
router(config)#int tun0
router(config-if)#shut
router#sho ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
Known via "static", distance 5, metric 0 (connected), candidate default path
Routing Descriptor Blocks:
* directly connected, via ATM0.1
Route metric is 0, traffic share count is 1
In this case shutting down the tunnel0 interface removed the route to that interface from the list of valid routes and there is no load sharing anymore.
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: Load Balancing of Unequal Ethernet Bandwidth
> To: td_miles at yahoo.com
> Cc: cisco-nsp at puck.nether.net
> Date: Monday, 16 February, 2009, 6:39 PM
> 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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