Re: [LARTC] Spill over

[Kenneth Kalmer <kenneth.kalmer@gmail.com>]

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Taylor & Chris (and the list)

The arguments behind my choice here is cost driven, the 64kbps line is a 
fixed monthly rate for unlimited use, the 512kbps line costs us roughly 
ZAR250 per 3GB of usage. This can get quite expensive as the lines in 
question is for a college and we all know what students do to bandwidth :)

Taken the amount we pay every month for the 64kbps line it's more economical 
to over utilize the link as a primary connection than to have it lying 
around as a backup. South Africa and data connections don't go well in the 
same sentence...

As Chris suggested, I need something that can detect when Link A is 
saturated and then redirect the traffic over Link B until there is available 
bandwidth on Link A again. The rate limit trick of Taylor might work once I 
get to understand the usage patterns of these students. But for at least the 
first 3 months I won't have proper data at my disposal.

Thanks for your replies!

On 4/24/05, Chris Bennett <chris@symbio.com> wrote:
> 
> You can't split a particular IP connection between two links, but can 
> instead only determine which link a particular connection will occur on. 
> Given this, it sounds like you want to have some way to detect that Link A 
> is already saturated and then send all further connections to Link B until 
> Link A is no longer saturated.
>  Maybe someone can tell you how to do that if that's really what you want 
> to do (others here know far more about this than me), but my guess is you 
> really don't want to do that. With the huge bandwidth disparity between the 
> two links, route cacheing, and the inability know how much bandwidth any 
> particular conneciton will consume, I think you'd end up with a giant 
> mess... those people with connections unlucky enough to end up on Link A 
> would probably be very unhappy people indeed.
>  Generally speaking I think it would make more sense to put all traffic 
> over Link B, and then use Link A only for emergencies. Maybe route the most 
> critical traffic over Link A if you really want to feel like its being 
> utilized as something other than a pure backup, but personally I wouldn't 
> even do that.
>  Just because Link A is more reliable and more expensive doesn't mean it 
> makes sense to use it as your primary conduit. With Link B having eight 
> times the bandwidth, it seems the obvious choice as the primary. Use it, and 
> keep the users happy most of the time (instead of making them miserable most 
> of the time). On the rare ocassions it goes down, use bandwidth shaping to 
> make sure the highest priority traffic gets access to Link A first.
>  In all the time I've used DSL, I've had severe outages twice for reasons 
> other than standard maintenance. In both cases (in two separate locations), 
> the cause was the ILEC phone company mistakingly dropping the wire pair 
> while doing other work (freakin took over a week in each case to get my 
> connectivity back!!). This sort of thing could just as easily happen with a 
> leased line though, so I'm not really sure I buy that the leased line is 
> really more reliable than DSL line from a high quality ISP. Although maybe a 
> particular SLA makes it so in some legal sense since you can then sue 
> someone. Personally, if your leased line really costs more than the DSL, I'd 
> get rid of it and get a 2nd DSL line from another provider and use that as 
> your backup instead.
>  Anyway, I guess my main point is that the high cost of your leased line 
> might be clouding your thinking on this. I wouldn't let the comparitive cost 
> be your guiding light here. Go with what makes sense from a technology 
> perspective, and don't guilt yourself into trying to get full utilization 
> out of the slow link just because it costs more.
>  
> ----- Original Message ----- 
> *From:* Kenneth Kalmer <kenneth.kalmer@gmail.com> 
> *To:* lartc <lartc@mailman.ds9a.nl> 
> *Sent:* Saturday, April 23, 2005 4:34 PM
> *Subject:* [LARTC] Spill over
> 
> List
> 
> I need some help, advice or just a starting point on the following 
> situation:
> 
> Link A - 64kbps leased line
> Link B - 512kbps ADSL line
> 
> Is it possible to have Link A saturated constantly and have the excess 
> traffic "spill over" onto Link B? I know it's possible to have packets sent 
> down links in a round-robin fashion and I've read in the howto on load 
> sharing over multiple interfaces (
> http://lartc.org/howto/lartc.loadshare.html), but I do not have control 
> over the termination of the link at the ISP's (two different one as well). 
> Also note that splitting different protocols over each of these links are 
> not possible in our case.
> 
> Reason being, Link A is a more reliable and more expensive link, so I need 
> to over-use it's capacity if it we're, and use the cheaper ADSL (link B) 
> offering to keep al services running when the leased line (A) is saturated.
> 
> Any tips, suggestions and comments would be welcomed.
> 
> Regards
> 
> -- 
> 
> Kenneth Kalmer
> kenneth.kalmer@gmail.com
> http://opensourcery.blogspot.com 
> 
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-- 

Kenneth Kalmer
kenneth.kalmer@gmail.com
http://opensourcery.blogspot.com

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