EQL Driver: Serial IP Load Balancing HOWTO
Simon “Guru Aleph-Null” Janes, simon@ncm.com
v1.1, February 27, 1995
This is the manual for the EQL device driver. EQL is a software device
that lets you load-balance IP serial links (SLIP or uncompressed PPP)
to increase your bandwidth. It will not reduce your latency (i.e. ping
times) except in the case where you already have lots of traffic on
your link, in which it will help them out. This driver has been tested
with the 1.1.75 kernel, and is known to have patched cleanly with
1.1.86. Some testing with 1.1.92 has been done with the v1.1 patch
which was only created to patch cleanly in the very latest kernel
source trees. (Yes, it worked fine.)
Introduction
Which is worse? A huge fee for a 56K leased line or two phone lines?
It’s probably the former. If you find yourself craving more bandwidth,
and have a ISP that is flexible, it is now possible to bind modems
together to work as one point-to-point link to increase your
bandwidth. All without having to have a special black box on either
side.
The eql driver has only been tested with the Livingston PortMaster-2e
terminal server. I do not know if other terminal servers support load-
balancing, but I do know that the PortMaster does it, and does it
almost as well as the eql driver seems to do it (– Unfortunately, in
my testing so far, the Livingston PortMaster 2e’s load-balancing is a
good 1 to 2 KB/s slower than the test machine working with a 28.8 Kbps
and 14.4 Kbps connection. However, I am not sure that it really is
the PortMaster, or if it’s Linux’s TCP drivers. I’m told that Linux’s
TCP implementation is pretty fast though.–)
I suggest to ISPs out there that it would probably be fair to charge
a load-balancing client 75% of the cost of the second line and 50% of
the cost of the third line etc…
Hey, we can all dream you know…
Kernel Configuration
Here I describe the general steps of getting a kernel up and working
with the eql driver. From patching, building, to installing.
2.1. Patching The Kernel
If you do not have or cannot get a copy of the kernel with the eql
driver folded into it, get your copy of the driver from
ftp://slaughter.ncm.com/pub/Linux/LOAD_BALANCING/eql-1.1.tar.gz.
Unpack this archive someplace obvious like /usr/local/src/. It will
create the following files:
______________________________________________________________________
-rw-r--r-- guru/ncm 198 Jan 19 18:53 1995 eql-1.1/NO-WARRANTY
-rw-r--r-- guru/ncm 30620 Feb 27 21:40 1995 eql-1.1/eql-1.1.patch
-rwxr-xr-x guru/ncm 16111 Jan 12 22:29 1995 eql-1.1/eql_enslave
-rw-r--r-- guru/ncm 2195 Jan 10 21:48 1995 eql-1.1/eql_enslave.c
______________________________________________________________________
Unpack a recent kernel (something after 1.1.92) someplace convenient
like say /usr/src/linux-1.1.92.eql. Use symbolic links to point
/usr/src/linux to this development directory.
Apply the patch by running the commands:
______________________________________________________________________
cd /usr/src
patch </usr/local/src/eql-1.1/eql-1.1.patch
______________________________________________________________________
2.2. Building The Kernel
After patching the kernel, run make config and configure the kernel
for your hardware.
After configuration, make and install according to your habit.
Network Configuration
So far, I have only used the eql device with the DSLIP SLIP connection
manager by Matt Dillon (– “The man who sold his soul to code so much
so quickly.”–) . How you configure it for other “connection”
managers is up to you. Most other connection managers that I’ve seen
don’t do a very good job when it comes to handling more than one
connection.
3.1. /etc/rc.d/rc.inet1
In rc.inet1, ifconfig the eql device to the IP address you usually use
for your machine, and the MTU you prefer for your SLIP lines. One
could argue that MTU should be roughly half the usual size for two
modems, one-third for three, one-fourth for four, etc… But going
too far below 296 is probably overkill. Here is an example ifconfig
command that sets up the eql device:
______________________________________________________________________
ifconfig eql 198.67.33.239 mtu 1006
______________________________________________________________________
Once the eql device is up and running, add a static default route to
it in the routing table using the cool new route syntax that makes
life so much easier:
______________________________________________________________________
route add default eql
______________________________________________________________________
3.2. Enslaving Devices By Hand
Enslaving devices by hand requires two utility programs: eql_enslave
and eql_emancipate (– eql_emancipate hasn’t been written because when
an enslaved device “dies”, it is automatically taken out of the queue.
I haven’t found a good reason to write it yet… other than for
completeness, but that isn’t a good motivator is it?–)
The syntax for enslaving a device is “eql_enslave
______________________________________________________________________
eql_enslave eql sl0 28800
eql_enslave eql ppp0 14400
eql_enslave eql sl1 57600
______________________________________________________________________
When you want to free a device from its life of slavery, you can
either down the device with ifconfig (eql will automatically bury the
dead slave and remove it from its queue) or use eql_emancipate to free
it. (– Or just ifconfig it down, and the eql driver will take it out
for you.–)
______________________________________________________________________
eql_emancipate eql sl0
eql_emancipate eql ppp0
eql_emancipate eql sl1
______________________________________________________________________
3.3. DSLIP Configuration for the eql Device
The general idea is to bring up and keep up as many SLIP connections
as you need, automatically.
3.3.1. /etc/slip/runslip.conf
Here is an example runslip.conf:
name sl-line-1
enabled
baud 38400
mtu 576
ducmd -e /etc/slip/dialout/cua2-288.xp -t 9
command eql_enslave eql $interface 28800
address 198.67.33.239
line /dev/cua2
name sl-line-2
enabled
baud 38400
mtu 576
ducmd -e /etc/slip/dialout/cua3-288.xp -t 9
command eql_enslave eql $interface 28800
address 198.67.33.239
line /dev/cua3
3.4. Using PPP and the eql Device
I have not yet done any load-balancing testing for PPP devices, mainly
because I don’t have a PPP-connection manager like SLIP has with
DSLIP. I did find a good tip from LinuxNET:Billy for PPP performance:
make sure you have asyncmap set to something so that control
characters are not escaped.
I tried to fix up a PPP script/system for redialing lost PPP
connections for use with the eql driver the weekend of Feb 25-26 ‘95
(Hereafter known as the 8-hour PPP Hate Festival). Perhaps later this
year.
About the Slave Scheduler Algorithm
The slave scheduler probably could be replaced with a dozen other
things and push traffic much faster. The formula in the current set
up of the driver was tuned to handle slaves with wildly different
bits-per-second “priorities”.
All testing I have done was with two 28.8 V.FC modems, one connecting
at 28800 bps or slower, and the other connecting at 14400 bps all the
time.
One version of the scheduler was able to push 5.3 K/s through the
28800 and 14400 connections, but when the priorities on the links were
very wide apart (57600 vs. 14400) the “faster” modem received all
traffic and the “slower” modem starved.
Testers’ Reports
Some people have experimented with the eql device with newer
kernels (than 1.1.75). I have since updated the driver to patch
cleanly in newer kernels because of the removal of the old “slave-
balancing” driver config option.
o icee from LinuxNET patched 1.1.86 without any rejects and was able
to boot the kernel and enslave a couple of ISDN PPP links.
5.1. Randolph Bentson’s Test Report
From bentson@grieg.seaslug.org Wed Feb 8 19:08:09 1995
Date: Tue, 7 Feb 95 22:57 PST
From: Randolph Bentson bentson@grieg.seaslug.org
To: guru@ncm.com
Subject: EQL driver tests
I have been checking out your eql driver. (Nice work, that!)
Although you may already done this performance testing, here
are some data I’ve discovered.
Randolph Bentson
bentson@grieg.seaslug.org
A pseudo-device driver, EQL, written by Simon Janes, can be used
to bundle multiple SLIP connections into what appears to be a
single connection. This allows one to improve dial-up network
connectivity gradually, without having to buy expensive DSU/CSU
hardware and services.
I have done some testing of this software, with two goals in
mind: first, to ensure it actually works as described and
second, as a method of exercising my device driver.
The following performance measurements were derived from a set
of SLIP connections run between two Linux systems (1.1.84) using
a 486DX2/66 with a Cyclom-8Ys and a 486SLC/40 with a Cyclom-16Y.
(Ports 0,1,2,3 were used. A later configuration will distribute
port selection across the different Cirrus chips on the boards.)
Once a link was established, I timed a binary ftp transfer of
289284 bytes of data. If there were no overhead (packet headers,
inter-character and inter-packet delays, etc.) the transfers
would take the following times:
bits/sec seconds
345600 8.3
234600 12.3
172800 16.7
153600 18.8
76800 37.6
57600 50.2
38400 75.3
28800 100.4
19200 150.6
9600 301.3
A single line running at the lower speeds and with large packets
comes to within 2% of this. Performance is limited for the higher
speeds (as predicted by the Cirrus databook) to an aggregate of
about 160 kbits/sec. The next round of testing will distribute
the load across two or more Cirrus chips.
The good news is that one gets nearly the full advantage of the
second, third, and fourth line’s bandwidth. (The bad news is
that the connection establishment seemed fragile for the higher
speeds. Once established, the connection seemed robust enough.)
#lines speed mtu seconds theory actual %of
kbit/sec duration speed speed max
3 115200 900 _ 345600
3 115200 400 18.1 345600 159825 46
2 115200 900 _ 230400
2 115200 600 18.1 230400 159825 69
2 115200 400 19.3 230400 149888 65
4 57600 900 _ 234600
4 57600 600 _ 234600
4 57600 400 _ 234600
3 57600 600 20.9 172800 138413 80
3 57600 900 21.2 172800 136455 78
3 115200 600 21.7 345600 133311 38
3 57600 400 22.5 172800 128571 74
4 38400 900 25.2 153600 114795 74
4 38400 600 26.4 153600 109577 71
4 38400 400 27.3 153600 105965 68
2 57600 900 29.1 115200 99410.3 86
1 115200 900 30.7 115200 94229.3 81
2 57600 600 30.2 115200 95789.4 83
3 38400 900 30.3 115200 95473.3 82
3 38400 600 31.2 115200 92719.2 80
1 115200 600 31.3 115200 92423 80
2 57600 400 32.3 115200 89561.6 77
1 115200 400 32.8 115200 88196.3 76
3 38400 400 33.5 115200 86353.4 74
2 38400 900 43.7 76800 66197.7 86
2 38400 600 44 76800 65746.4 85
2 38400 400 47.2 76800 61289 79
4 19200 900 50.8 76800 56945.7 74
4 19200 400 53.2 76800 54376.7 70
4 19200 600 53.7 76800 53870.4 70
1 57600 900 54.6 57600 52982.4 91
1 57600 600 56.2 57600 51474 89
3 19200 900 60.5 57600 47815.5 83
1 57600 400 60.2 57600 48053.8 83
3 19200 600 62 57600 46658.7 81
3 19200 400 64.7 57600 44711.6 77
1 38400 900 79.4 38400 36433.8 94
1 38400 600 82.4 38400 35107.3 91
2 19200 900 84.4 38400 34275.4 89
1 38400 400 86.8 38400 33327.6 86
2 19200 600 87.6 38400 33023.3 85
2 19200 400 91.2 38400 31719.7 82
4 9600 900 94.7 38400 30547.4 79
4 9600 400 106 38400 27290.9 71
4 9600 600 110 38400 26298.5 68
3 9600 900 118 28800 24515.6 85
3 9600 600 120 28800 24107 83
3 9600 400 131 28800 22082.7 76
1 19200 900 155 19200 18663.5 97
1 19200 600 161 19200 17968 93
1 19200 400 170 19200 17016.7 88
2 9600 600 176 19200 16436.6 85
2 9600 900 180 19200 16071.3 83
2 9600 400 181 19200 15982.5 83
1 9600 900 305 9600 9484.72 98
1 9600 600 314 9600 9212.87 95
1 9600 400 332 9600 8713.37 90
5.2. Anthony Healy’s Report
Date: Mon, 13 Feb 1995 16:17:29 +1100 (EST)
From: Antony Healey ahealey@st.nepean.uws.edu.au
To: Simon Janes guru@ncm.com
Subject: Re: Load Balancing
Hi Simon,
I’ve installed your patch and it works great. I have trialed
it over twin SL/IP lines, just over null modems, but I was
able to data at over 48Kb/s [ISDN link -Simon]. I managed a
transfer of up to 7.5 Kbyte/s on one go, but averaged around
6.4 Kbyte/s, which I think is pretty cool. :)
