Geovana Navarro wrote:

>I have two Internet connections (2 ISPs) use shorewall to balance 
>the load, and this works well, is it possible to obtain the sum of 
>the two ISP or at least have a larger bandwidth to an ISP?
>
>Load Balancing for me is to distribute the different flows between 
>an ISP and the other, respecting the bandwidth of each of them and 
>get more bandwidth on my connection, and not to limit the bandwidth 
>of a single link (ose to an ISP).
>
>ISP1 =6Mbps
>ISP2 =6Mbps
>ISP-Total= 12 Mbps

OK, you seem to lack understanding of what the limitation is.
Your connection to ISP1 is limited to 6M<period> If that's what the 
limit is, then you cannot get more than that. The same for ISP2.
So just because the combined throughput is 12M does **NOT** mean you 
can get more than 6M to either ISP - each is still limited to 6M.

So no, just by not running traffic through one connection, you cannot 
magically get 12M through the other (or even 6.1M). In the same way, 
you can't get yourself a high-performance car by buying two low 
performance ones and leaving one in the garage !

The other thing to realise is that without active assistance from the 
ISP(s) or a third party, you cannot actually load balance across two 
connections anyway. You can "sort of as long as you don't look too 
hard at what's going on" do it, but it's not true load balancing and 
does cause some problems.

The first thing is that any single established connection **cannot** 
use more than one ISP link. You might get away with sending packets 
down the "other" ISP for it's IP address, but most ISPs will filter 
these and drop them. You 100% will not get any inbound packets via 
the "other" ISP.

So if you are downloading a large file with something like FTP or 
HTTP, then it cannot use more bandwidth than that available on ONE of 
your links.

Where multiple streams are involved, then the "load balancing" as 
done with Shorewall can only distribute connections between links. 
With a large number of randomish connections then the resulting 
bandwidth will appear to be balanced - but if one of those 
connections then uses a lot of bandwidth (such as the previously 
mentioned file download), then your traffic will be unbalanced.

Also, be aware that if the connection distribution is properly 
randomised then this can cause problems - eg a website sees some of 
your requests come from one IP, and some from a different IP. Some 
sites may see this as the same user logged in from two places and 
either get confused and not work properly, or may flag it as an 
attack and lock you out.

-- 
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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