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.)
1. 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...
2. 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.cUnpack 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.
3. 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 1006Once 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 <master-name> <slave-name> <estimated-bps>". Here are some example enslavings:
eql_enslave eql sl0 28800 eql_enslave eql ppp0 14400 eql_enslave eql sl1 57600When 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.
4. 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.
5. 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.
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 301.3A 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 kbit/sec
mtu
seconds duration
theory speed
actual speed
%of 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. :)