LinuxSA Mailing list archives

  From: Glen Turner <glen.turner@aarnet.edu.au>
  To  : <linuxsa@linuxsa.org.au>
  Date: Sat, 09 Dec 2000 16:42:04 +1030

Re: "Host based" routers and BGP

On Fri, 8 Dec 2000, David Newall wrote:
>
> Would a PC be suitable?  That's what Jason is trying to find out.
> Apparently PC hardware is reliable enough; it won't break down every week or
> even every month.

This isn't at all clear.  I've just read a paper on packets
that had TCP/UDP checksum errors despite having fine link
layer CRCs. [1]

Such packets were present in 1 in 1,500 to 1 in 20,000
packets.  1 in 20,000 is a very common if you think in
packets/second terms.

A major cause of these errors was cheap hardware in hosts.
In particular
  - memory
  - motherboards
  - ethernet interfaces

The moral seems to be that if you are planning to use a PC-based
router then you need to buy from the high end of the market.

Similarly, the names "Intel" , "3Com", "Cisco", "HP", "Compaq"
were prominent by their absence in the listings of malfunctioning
gear.  "DLink" and "Apple" appeared too often for my liking.

Serial overruns also seem to be a problem: this comes down
to UARTs and configuring CTS/RTS handshaking on the modem.

Even one additional bad packet per second generated by a router
will cause a huge backoff for the two communicating hosts, and
thus undo any headline packets-per-second figure.

Glen

[1] J Stone & C Partridge
    "When the CRC and TCP checksum disagree"
    in "Proceedings of the ACM SIGCOMM 2000 conference.  Applications
        technologies, architectures and protocols for computer
        communication."  Held Stockholm, Sweden 2000-08-28 to
2000-09-01.
       Association for Computing Machinery, Special Interest Group on
       Data Communication.  New York, NY, USA.  2000.

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