06-28-2014
You can create VLANs,not for common communication, but to isolate layer-2 communication from other network objects. Security.
Example:
If I am on VLAN A I may not be able to ssh over to VLAN B. A lot of places will do this with development versus production servers. Code librarians work on VLAN C with access to A and B. DMZ's are another possible example of isolation at the layer-2 level. Layer-1 isolation is the same idea. If bad guys cannot see network object at all it cannot be attacked. Air gap attacks notwithstanding.
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LEARN ABOUT DEBIAN
nncheck
NNCHECK(1) General Commands Manual NNCHECK(1)
NAME
nncheck - check for unread articles
SYNOPSIS
nncheck [ -Q -r -t ] [ -f format ]
DESCRIPTION
nncheck will report if there are some articles on the system which you have not read.
Without options, nncheck will simply print a message reporting the number of unread articles with the following format:
There are 327 unread articles in 25 groups
and when there are no unread articles, the following message will be printed:
No News (is good news)
nncheck will exit with a value of 0 if there are unread articles, and 99 if there is no news (see the exception for the -r option.)
It is important to notice that even though unread articles have been reported by nncheck, the actual number of unread articles may be much
lower (or even zero) when nn is invoked to read the articles. This is because the calculation of the number of unread articles is only
based on recorded article number intervals. Invoking nn to read the articles may reveal that the articles have previously been read in
another news group, have been expired, or are killed using the auto-kill facility.
The following options are used to modify the amount and format of the output from nncheck:
-Q Quiet operation. No output is produced, only the exit status indicate whether there is unread news.
-t Print the name of each group with unread articles, and how many unread articles there are (not counting split digests!).
-r Output a single integer value specifying the number of unread articles, and exit with a 0 status (somebody told me this would be
useful).
-f format
Output the number of unread articles using the specified format. The format is a text that may contain the following %-escapes:
%-code resulting output
%u "uuu unread articles"
%g "ggg groups"
%i "is" if 1 unread article, else "are"
%U "uuu"
%G "ggg"
where uuu is the number of unread articles, and ggg is the number of groups with unread articles.
For example, the default output format is
"There %i %u in %g"
which I prefer to the following less perfect format:
"There are %U unread article(s) in %G group(s)"
FILES
~/.newsrc The record of read articles
$db/MASTER The database master index
SEE ALSO
nn(1), nngoback(1), nngrab(1), nngrep(1), nnpost(1), nntidy(1)
nnadmin(1M), nnusage(1M), nnmaster(1M)
AUTHOR
Kim F. Storm, Texas Instruments A/S, Denmark
E-mail: storm@texas.dk
4th Berkeley Distribution Release 6.6 NNCHECK(1)