Update of /cvsroot/devil-linux/build/scripts/configuration/help
In directory sc8-pr-cvs12.sourceforge.net:/tmp/cvs-serv25468/scripts/configuration/help
Added Files:
dcc.help
Log Message:
- updated razor-agents-2.84.tar.bz2
- updated kernel to 2.6.24.4
- updated pax-linux-2.6.24.4-test36.patch.bz2
- updated gradm-2.1.11-200803102037.tar.gz
- updated grsecurity-2.1.11-2.6.24.4-200803251800.patch.bz2
- updated Linux-PAM to 0.99.10.0
- su is now wokring again
- updated open-vm-tools to 2008.03.19-82724
- updated shadow 4.1.0
- added libdnet 1.11
- updated pam configurations files from BLFS book
- corrected permissions on su
and some code cleanup
--- NEW FILE: dcc.help ---
CONFIG_DCC
The DCC or Distributed Checksum Clearinghouse is an anti-spam content filter
that runs on a variety of operating systems. As of the middle of 2007, it
involves millions of users, more than one hundred thousand client computer
systems, and more than 250 servers collecting and counting checksums related
to more than 300 million mail messages on week days. The counts can be used
by SMTP servers and mail user agents to detect and reject or filter spam or
unsolicited bulk mail. DCC servers exchange or "flood" common checksums. The
checksums include values that are constant across common variations in bulk
messages, including "personalizations."
The idea of the DCC is that if mail recipients could compare the mail they
receive, they could recognize unsolicited bulk mail. A DCC server totals
reports of checksums of messages from clients and answers queries about the
total counts for checksums of mail messages. A DCC client reports the checksums
for a mail message to a server and is told the total number of recipients of
mail with each checksum. If one of the totals is higher than a threshold set by
the client and according to local whitelists the message is unsolicited, the
DCC client can log, discard, or reject the message.
Because simplistic checksums of spam would not be effective, the main DCC
checksums are fuzzy and ignore aspects of messages. The fuzzy checksums are
changed as spam evolves. Since the DCC started being used in late 2000, the
fuzzy checksums have been modified several times.
Unless used with isolated DCC servers and so losing much of its power,
the DCC causes some additional network traffic. However, the client-server
interaction for a mail message consists of exchanging a single pair of UDP/IP
datagrams of about 100 bytes. That is often less than the several pairs of
UDP/IP datagrams required for a single DNS query. SMTP servers make DNS queries
to check the envelope Mail_From value and often several more. As with the
Domain Name System, DCC servers should be placed near active clients to reduce
the DCC network costs. DCC servers exchange or flood reports of checksums, but
only the checksums of bulk mail. Since most mail is not bulk and only
representative checksums of bulk mail need to be exchanged, flooding checksums
among DCC servers involves a manageable amount of data.
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