Comments on: Load Balancing two ISPs

By: Niels Horn

Niels Horn — Tue, 22 Mar 2011 12:07:20 +0000

Hello,

In this case – having the same gateway – my solution won’t work for you…
But it should be possible to adapt it to your setup. The problem is I can’t test it for you here

You might try using “via a.b.c.d” where a.b.c.d is the internal IP address of the NIC connected to your adsl modem, instead of the gateway address.
But – as I said – I have not tried this here…

By: A. Orta

A. Orta — Tue, 22 Mar 2011 00:25:52 +0000

Hi,

I tried this script but under my circumstances does not work. I have 2 adsl bridged modems from the same ISP and I connected it via pppoe. The problem is that I have the same default gw for ppp0 and ppp1. When only one link is up it works perfectly but when I start the second and run the script the two links goes “down”(not really because when I shut down one the other begin to work). Do you need more details? Any help will be appreciated.

P.S. I use Slackware too.

By: Niels Horn

Niels Horn — Sat, 27 Mar 2010 15:09:57 +0000

@aspnair:
IIRC, pppd should create the gateway. You might have to set the “defaultroute” parameter in your pppd configuration file, or use it as an option when calling pppd.

By: aspnair

aspnair — Wed, 24 Mar 2010 14:03:50 +0000

I just modified the script to find out the ppp0 gateway from ifconfig itself.
Following is my modification.

gw2=$(route -n | grep $DEV2 | grep ‘^0.0.0.0′ | awk ‘{print $2}’)
if [ "$gw2" == "" ]
then
gw2=$(ifconfig $DEV2 | grep P-t-P | awk ‘{print $3}’ | awk -F: ‘{print $2}’)
fi

I tried dialing using pon with pppd and wvdial. It looks like, they dont add a default route
when it sees another active default route, eth0 interface in this case.

By: Niels Horn

Niels Horn — Wed, 24 Mar 2010 11:08:30 +0000

@aspnair:
It seems that when you use your GSM modem, it is not recognized as a gateway in your routing table.
I use a script to “dial” my ISP with my GSM modem that automatically adds it as a gateway, so the balancing script finds it when I start that.
Setting the gw2 variable manually works, but it would be best to set the gateway on your ppp connection.
Anyway, thanks for your feedback!

By: aspnair

aspnair — Wed, 24 Mar 2010 10:54:43 +0000

Hello Niels….This is a wonderful post. Thanks.
I was following your link.
My linux machine is behind a NAT router and it is connected to the router/switch using eth0. For the other connection I use a GSM broadband modem (ppp0). I could get it working after making one change from your script, for now I did that manually.

For my case, “ifconfig ppp0″ is
ppp0 Link encap:Point-to-Point Protocol
inet addr:115.117.135.93 P-t-P:172.29.243.129 Mask:255.255.255.255
……
route -n | grep ppp0
……
172.29.243.129 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0
0.0.0.0 0.0.0.0 0.0.0.0 U 0 0 0 ppp0
……
From your script.. gw2=`route -n | grep $DEV2 | grep ‘^0.0.0.0′ | awk ‘{ print $2 }’`
gw2 becomes ‘0.0.0.0′ and this was not working.
But instead of that when I changed gw2 to 172.29.243.129, then things were working.

By: Niels Horn

Niels Horn — Thu, 07 Jan 2010 14:10:24 +0000

Both links should be equally used, but only if you have several simultaneous connections (like my example downloading with some torrent software). If you are downloading a large file from a single IP, there will be only one IP-to-IP connection that cannot be balanced between two links, as the sending IP can only send data to one destination for a single download.

With torrent software you will have many simultaneous connections, downloading different parts from different peers. In this case the balancing works fine.

By: balaji rm

balaji rm — Thu, 07 Jan 2010 11:36:13 +0000

hi,
could you please help me out where in i get even (same)speed across two ip’s say 100kbits/sec through two ett0 and ppp0.

By: niels.horn

niels.horn — Mon, 12 Oct 2009 12:12:56 +0000

@gmbastos: You're right, it can be done in a shorter line. Like they say "there are many ways to Rome".
I kept the script as simple & clear as possible to make it easier to understand. But everyone is free to improve it like you did.
Awk if an extremely powerful tool and I sometimes think I only use like 10% of its power…

By: gmbastos

gmbastos — Mon, 12 Oct 2009 07:08:16 +0000

Hello, Niels.

Thank you for this great post.

But, even though you are far more experienced than me in scripting, I dare to tell you that awk can make that IP address extraction in one run (I'm referring to your load balance script):

# Get IP addresses of our devices:
ip1=`ifconfig $DEV1 | awk '/inet addr:/ { split($2,inetline,":"); print inetline[2]}'`
ip2=`ifconfig $DEV2 | awk '/inet addr:/ { split($2,inetline,":"); print inetline[2]}'`

As you work with heavy-weight servers, perhaps this can make some difference (for a SOHO user speed and footprint improvements are unnoticeable).