morrison@accuvax.nwu.edu (Vance Morrison ) (08/09/89)
Hello,
Well, at long last, PCroute2.0 is available for anonymous FTP
from accuvax.nwu.edu (129.105.49.1). Both the executable and
the source can be found in the directory ~ftp/pub/pcroute.
I am planning on talking to uunet to see if I can put the code
there so that people without internet access can get at the code.
So if you can't FTP, please be patient.
Version 2.0 is a big step forward for PCroute. In particular
SLIP support has now been added. For those unfamiliar with PCroute
here is a short description.
Vance
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PCROUTE - an IP routing program from the IBM PC
Vance Morrison
morrison@accuvax.nwu.edu
Traditionally IP routers have been fairly high performance,
expensive machines. Typically they run about $5000-$10,000 a unit.
Until now a IP router for under $5000 was just about impossible
to get. Recent developments in PC hardware, however, has made
it possible to convert a PC to an IP router for a TOTAL of $800
a unit. This price is less that the cost of many ethernet boards
and thus it now makes sense to always use dedicated router to
perform IP gatewaying functions.
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What is PCroute?
PCroute is software written for an PC/XT (or AT) or clone that will
allow it to act as a IP router. At present the following interfaces
are supported.
Ethernet - (WD8003E card) (recommeded no more than 4 interfaces)
Starlan - (WD8003S card) (up to 6 interfaces)
Localtalk - (Apple localtalk card for the PC) (1 interface max)
SLIP - (COM1..COM4) (2 interfaces max)
One of the most common configuration for the router is as an
ethernet-ethernet router, but this is not the only configuration possible.
The software supports up to 6 interfaces of varying types, so many
many configurations are possible. Exact details on what is possible
is explained in the installation/compilation manual
In addition to the XT, the only other hardware needed are the
networking cards, which at present run about $225 a piece (for ethernet).
Since you can buy an XT (10Mhz, without an monitor) for $350, the total
cost for the hardware is $800
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What do I need to install PCroute?
1) An XT computer (does not need monitor) with a floppy
2) The proper interface cards
Ethernet : WD8003E Ethercard Plus
Starlan : WD8003S,WD8003SH Starcard,Starlink Plus
Localtalk: Apple localtalk PC card
SLIP : COM[1-4] ports
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How Fast is PC route?
Some may argue that a PC simply is not fast enough to be a
good IP router. For slow networks (Localtalk SLIP) this is not really
an issue. For Ethernet it is a real concern. Luckily, in the case
of Ethernet (and starlan), the Western Digital cards do a lot of the work.
All the input packet queuing is done by the card, freeing the PC to do the
routing task. By programming in assembler and optimizing for peak
efficiency (the main loop has NO procedure calls), the PC is up to the task.
Actual tests indicate that that following formula is a worst case
estimate of the throughput of PCroute on a 4.77Mhz XT (based on actual
measurments).
packet_delay = .51 + .00406 * len msec
Where 'len' is the length of the packet in bytes. Thus PCroute has a
fixed per packet overhead of .51 msec and takes .00406 msec/byte to transfer
the packet from one network to the other.
Thus for the largest packet size (1514) we get throughput of
packet_delay = .51 + .00406 * 1514 = 6.65 ms
throughput = len*8/packet_delay = 1.8 Mbit/sec
For the smallest packet size (64) we get a throughput of
packet_delay = .51 + .00406 * 64 = .77 ms
throughput = len*8/packet_delay = .66 Mbit/sec
If you are going to by the XT needed, please buy a clone (without
a monitor) with a 10Mhz CPU speed (cost < $350). This will almost
double the throughput measured above. If you need more speed you can
go with an AT clone and a even faster CPU speed. Here are some
actual measurements of packet speeds for some common machines.
per packet per byte Packet rate Throughput
delay delay (64bytes) (1500 bytes)
-----------------------------------------------------------------------------
4.77 Mhz XT | .51 msec .00406 msec 1300 /sec 1.8 Mbits/sec
10 Mhz XT | .237 msec .00254 msec 2500 /sec 3.0 Mbits/sec
6 Mhz AT | .169 msec .00228 msec 3200 /sec 3.3 Mbits/sec
12 Mhz AT (est)| .100 msec .00220 msec 4150 /sec 3.5 Mbits/sec
16 Mhz AT | .050 msec .00190 msec 5800 /sec 4.1 Mbits/sec
As you can see, at the high end, the PCrouter can sustain a thoughput
of close to half the BANDWIDTH of a ethernet (remember 5Mbits of sustained
load is a HEAVY load for an ethernet). Also remember that this is packets
routed THOUGH the router. Thus even if 4/10 of the ethernet bandwidth is
being used (that is your ethernet is HEAVILY loaded) and ALL that traffic
is going though the router, PCroute can still keep up.
Note also that the throughput measurements are based on packet delay.
This tends to underestimate the thoughput of the router since it ignores
the fact that there are in fact three processes in the router that are
doing work concerently. Thus the router can actually handle slightly more
traffic than what the above figure would indicate.
In addition the Ethernet boards have an on-board 6.5K packet input buffer.
Thus packets that come at the PCrouter too fast for it to process will be
queued. This queueing happens on board and can keep up with the maximum
10Mbit/sec bit rate. Thus the router will start dropping packets only
after this 6.5K buffer is exhausted.
Note that since SUN NFS likes to send 8K blocks in fast spurts
this will sometimes cause the router to drop packets (since this is
larger than the input queue buffer size). If you are running NFS through
the router, I suggest that you set the NFS block size down to 4K for
file systems that are mounted though the router (look for 'rsize' and
'wsize' in man fstab). We use NFS quite heavily here at NU and as
long as rwize and wsize are set to 4K we have no problem.
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What about SLIP speeds?
PCroute also supports up to 2 serial lines in addition to the other
interfaces. These lines can operate at all the common baud rates
up to 19.2K. In PCroute with a faster processor (10Mhz XT or an AT clone)
can handle 38.4K or even 57.6K. All of this using the standard 8250
serial ports.
Note because PC serial ports interupt the processor on EVERY character
SLIP consumes a fair amount of the CPU. On a 4.77MHZ XT the interupts
for two SLIP ports running at 19.2K Baud consume about 1/2 the available
CPU time. (actually measurements show that two slip lines running full
tilt at 19.2K consume slightly less than 1/2 the CPU). Thus packet delays
will double. Obviously the situation gets better as CPU speed increases.
On a 12Mhz AT interupts consume less than 1/10 of the CPU.
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What PC route supports?
PCroute was designed to be a fully functional IP router. In
particular it supports
1) IP routing with Subsets (however the subnet mask
must begin with 255.255)
2) Static routing with up to 250 routes.
3) responds to ICMP echo (ping)
4) Sends ICMP TTL, Redirect, Unreachable when appropriate
5) Fragmentation where necessary
6) RIP dynamic routing protocol
7) Up to 6 interfaces of varying types
8) Error logging using BSD syslog
9) Optional proxy ARP
10) Bootp forwarding
Note that although the software supports up to 6 interfaces, the
total throughput of the router is fixed by the speed of the processor.
For fast boards (ethernet) this gets excessive after 4 interfaces
are installed.
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What PC route DOESN'T support?
1) Ethernet cards besides WD8003E. It is possible to write
the driver code for other cards, but I personally have no
desire to do so.
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Wish List
These are things that I would like to add to PCroute, but it looks like
I will not have the time.
1) SNMP support. Everybody wants SNMP support. Well there is
nothing that says PCroute can't have it. I have written the
code with this support in mind. In addition, some people at CMU
have already written the hard part of SNMP and all that would
be necessary is to graft that code onto the various databases
inside PCroute. I think this would take about 1-2 months of
half time progamming effort.
2) Any other interface that someone might what (T1 or X.25 for
example). PCroute has been designed to make this addition
relatively simple.
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Hints
1) We found that the 10Mhz XT clones that Jamco and others sell
work very well. One nice feature about these units is their
BIOS. By setting the dip switches in the PC, you can tell it
that there is no Monitor. This also tells the BIOS not to
check for a keyboard either. Thus you don't need to buy either
the keyboard or the monitor. Other XT BIOS ALWAYS check for
the keyboard, and thus you have to plug it in even though you
never use it.
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Reliability
The reliability of PCroute has been EXCELLENT. We have been
using these routers for months now in ten places with absolutely
no failures. If you wish to PING one for yourself here are some
PC routers on our campus
129.105.49.13
129.105.1.1
129.105.7.1
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Comments and Bug reports
I am interested in finding out what you think of PCroute and
how well it performs for you. I am also interested in hearing
about any problems you have or bugs in the documentation.
You should send your comments to
Vance Morrison <morrison@accuvax.nwu.edu>
Note that since I am not paid to support this software, I can
not guarantee that I can respond to your problem, but I will
try.
Vance Morrison
Northwestern University