On Wed, 23 Jan 2008 11:12:57 -0500, "Bill Kearney"
<wkearney99@hotmail.com> wrote:

>I was a bit suprised to see the old 3-4-5 rule has less applicability
>(none?) with switches.

It's the 5-4-3 rule. It's totally non-applicable to ethernet switches
and only applies to hubs (i.e. ethernet repeaters).
<http://en.wikipedia.org/wiki/5-4-3_rule>
Hubs are useful sacrificial offerings. See below.

>I'd still want to avoid stringing things along
>through too many devices, if just to avoid debugging nightmares. But a
>typical residential setting (or even a small office) isn't likely to run
>into things like arp cache overflows and the like.

Not the ARP cache but the MAC address to port number table as found in
all ethernet switches. The cheap switches just discard as fast as
possible. The good switches have huge table space and keep the table
populated as long as possible. I had to deal with an Allied Telesyn
switch that had exactly 1 slot in the table as it was assumed that the
backbone was connected to a router, which (usually) requires only a
single MAC address. It's a rare problem, but I've seen it.

However idiots like me are certainly capeable of doing something
similar. It seems that one of my coffee shop customers was
complaining that *SOME* customers are connecting, but not getting DHCP
assigned IP's. An important clue was that regular customers were
working, while new customers and visitors were not getting IP's.

Dumping the DHCP lease database from DD-WRT v24 sp3 (old), I found
that the table had filled up all 100 addresses that I allowed in the
DHCP addressable space. It had saved 100 leases and said it's time to
give up. After upgrading to v24 RC6.2, I found a check box to
"Save DHCP table in NVRAM".
Unchecking the box allowed the DHCP lease database to flush normally.

>At least the damage stopped there, not followed along the wire and to the
>computers themselves.

I have a sacrificial ethernet hub at each end of the link. One of the
media converters was smoked, as were both hubs. Sacrifices must be
made to the thunder gods. A $10 junk hub apparently placated the
thunder god's anger and restored connectivity to us mere mortals.

As far as following the rules are concerned, I rarely do that. My
definition of experience is knowing what rules can be broken, under
what circumstances, and with what limitations.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 jeffl@comix.santa-cruz.ca.us
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS