[152232] in North American Network Operators' Group
Re: Most energy efficient (home) setup
daemon@ATHENA.MIT.EDU (Steven Bellovin)
Thu Apr 19 18:39:04 2012
From: Steven Bellovin <smb@cs.columbia.edu>
In-Reply-To: <4F90924F.6030300@mail-abuse.org>
Date: Thu, 19 Apr 2012 18:37:32 -0400
To: Douglas Otis <dotis@mail-abuse.org>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Apr 19, 2012, at 6:31 43PM, Douglas Otis wrote:
> On 4/18/12 8:09 PM, Steven Bellovin wrote:
>>=20
>> On Apr 18, 2012, at 5:55 32PM, Douglas Otis wrote:
>> > Dear Jeroen,
>> >
>> > In the work that led up to RFC3309, many of the errors found on the
>> > Internet pertained to single interface bits, and not single data
>> > bits. Working at a large chip manufacturer that removed internal
>> > memory error detection to foolishly save space, cost them dearly in
>> > then needing to do far more exhaustive four corner testing.
>> > Checksums used by TCP and UDP are able to detect single bit data
>> > errors, but may miss as much as 2% of single interface bit errors.
>> > It would be surprising to find memory designs lacking internal
>> > error detection logic.
>>=20
>> mallet:~ smb$ head -14 doc/ietf/rfc/rfc3309.txt | sed 1,7d | sed
>> 2,5d; date Request for Comments: 3309
>> Stanford September 2002
>>=20
>> Wed Apr 18 23:07:53 EDT 2012
>>=20
>> We are not in a static field... (3309 is one of my favorite RFCs --
>> but the specific findings (errors happen more often than you think),
>> as opposed the general lesson (understand your threat model) may be
>> OBE.
> Dear Steve,
>=20
> You may be right. However back then most were also only considering =
random single bit errors as well. Although there was plentiful evidence =
for where errors might be occurring, it seems many worked hard to ignore =
the clues.
>=20
> Reminiscent of a drunk searching for keys dropped in the dark under a =
light post, mathematics for random single bit errors offer easier =
calculations and simpler solutions. While there are indeed fewer =
parallel buses today, these structures still exist in memory modules and =
other networking components. Manufactures confront increasingly =
temperamental bit storage elements, where most include internal error =
correction to minimize manufacturing and testing costs. Error sources =
are not easily ascertained with simple checksums when errors are not =
random.
>=20
Yes -- that's precisely why I like that RFC so much.
--Steve Bellovin, https://www.cs.columbia.edu/~smb
