On Tue, 5 Jun 2001 wojtek@wojtek.3miasto.net wrote:

> > I can tell you from experience that not using checksums is inviting disaster.
> 
> doesn't ethernet has it's own layer-2 checksumming?

[snip]

<sarcasm>Yes, and the entire world is connected by ethernet</sarcasm>

Seriously, how many people still dial up?  How many people out there have
anything from DS0s to T1s to T3s to OC-12s to DWDM?  What about
DSL?  When I use my home lines, I hit three separate subnets via ethernet
before riding a DSL line out to my provider, who probably has a T3 or
OC-x, which rides anything from ethernet to gigabit to hippi to hssi out
to my destination.  Where's the end-to-end CRC then?  Aha!  It's on the IP
and UDP packets.  Where's the ethernet checksum?  It was dropped when it
hit my first gateway, right at home.  It didn't even make it past my file
cabinet.

There's a good quote midway down a page on EFTP (which can be found at
http://web.mit.edu/6.033/1998/www/reports/r04-jdoering.html) which
describes why, when using Ethernet-FTP, it's still important to have a
second checksum.

-
Jon
 --------------------------------------------------------------------
 "'The chicken,' it's been said, 'is just an eggs way of making more
  eggs.'" -- Alton Brown