ProfitPress Mega CDROM2 …eeware (MSDOS)(1992)(Eng)/ProfitPress-MegaCDROM2.B6I/MISC/NETWORK/PCRTE220.ZIP/README.DOC

Text File | 1991-02-08 | 12.0 KB | 249 lines

            PCROUTE - an IP routing program from the IBM PC
                             Vance Morrison
                        [e-mail]

    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 $700
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,WD8003EBT,WD8013EBT) (recommended <= 4 interfaces)
                 - (Any card supported by the Packet Driver)
        Starlan  - (WD8003S card) (up to 6 interfaces)
        Localtalk - (Apple localtalk card for the PC) (1 interface max)
        SLIP      - (COM1..COM4)  (up to 6 interface)

   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 $190 a piece (for ethernet).
Since you can buy an XT (10Mhz, without an monitor) for $300, the total
cost for the hardware is $700

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What do I need to install PCroute?

        1) An XT or AT computer (does not need monitor) with a floppy
        2) The proper interface cards
                Ethernet : WD8003E,WD8003EBT, or WD8013EBT
                         : Any card and its packet driver
                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 with WD8003E cards indicate that that following formula
is a worst case estimate of the throughput of PCroute on a 4.77Mhz XT
(based on actual measurements).

        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 < $300).  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 throughput
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.

   The above measurements where made with WD8003E cards. Since copy time
is the major bottleneck, and WD8013EBT cards have a 16 bit instead of
an 8 bit data path, it is likely that throughput would almost double if
that card was used.

   In addition the Ethernet boards have an on-board input buffer.
Thus packets that come at the PCrouter too fast for it to process will be
queued.  This queuing happens on board and can keep up with the maximum
10Mbit/sec bit rate.  Thus the router will start dropping packets only
after this buffer is exhausted.

   Unfortunately, the WD8003E card has only enough space for a 6.5K input
buffer.  Since many file servers (SUN NFS), like to send 8K blocks,
PCroute can loose packets if WD8003E cards are used.  Thus if you
expect NFS traffic through the router, it is STRONGLY recommended that
you use WD8003EBT, or WD8013EBT cards.  These cards have larger buffers
and thus will not drop packets when 8K blocks are sent quickly.

If you are stuck with WD8003E cards and need to run NFS, it may be possible
to tell NFS to send smaller blocks by setting the 'rsize' and 'wsize'
parameters in fstab.  This seems to only work with some versions, however,
so it is not the preferred solution.

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What about SLIP speeds?

    PCroute also supports up to 6 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 interrupt the processor on EVERY character
SLIP consumes a fair amount of the CPU.  On a 4.77MHZ XT the interrupts
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 interrupts consume less than 1/10 of the CPU.

If you are buying new cards, buy com boards with the 16550AF chip.  This
chip has a FIFO that will store up to 16 characters before interrupting
the CPU.  Thus these chips will load the CPU only about 1/10 that of
the 8250.  Using com ports with this chip, even a 4.77 XT could handle
many ports (4) at high baud rate (57.6K) with no problem.

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What is localtalk support?

    PCroute supports IP inside of localtalk (appletalk).  This allows
you to send IP packets though localtalk nets.  Since localtalk can
be sent over twisted pair (phonenet) large distances (5000 ft with
a star controller), this method has many of the advantages of SLIP
and is a higher speed solution.  In addition any MACs on the localtalk
network that have MacTCP can access the IP network.

    Note, however that PCroute does NOT support encapsulating appletalk
in IP.  This is important because it is a major limitation.  Any
application like CAP that makes IP hosts look like normal appletalk
file or print servers, or lets IP hosts use laserwriters will not work.
Basically the only thing PCroute will let you do is run MacTCP applications
so that Macs can access IP related services.  Also PCroute does not
support IP address allocation.  Thus all the Macs must either be
given a static IP address or generate one dynamically from its localtalk
address.  PCroute will not 'give out' addresses like KIP boxes will.

    Also note that this limitation is unlikely to change.  There are
no plans for supporting more advanced localtalk features.  (It would
take a LOT of work).

    Note also that PCroute's implementation is known NOT to work with
some older MacIP software (most notablely NCSA-Telnet that does not
used MacTCP).  It does work with MacTCP.  This is all I will say.

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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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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 programming effort.

        2) Any other interface that someone might want (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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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 <[e-mail]>

        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