
    Distributed Checksum Clearinghouse (DCC) Frequently Answered Questions

   Current versions of this list can be found among the DCC web pages
   and their mirror.
     * What is the Distributed Checksum Clearinghouse or DCC?
     * Do the fuzzy checksums ignore "personalizations"?
     * How much bandwidth, disk space, and computing does the DCC
       require?
     * Do I need to run a DCC server?
     * What happens to my mail if the DCC crashes?
     * How do I mark spam without rejecting it?
     * Why doesn't the man command find the man pages?
     * Must sendmail be used with the DCC?
     * How can the DCC be used with qmail?
     * Can the DCC be used with smtpd?
     * Can the DCC be used with Exim?
     * How can the DCC be used with mail user agents?
     * Can the DCC be used with SpamAssassin or other spam filters?
     * Must I have the root password to use the DCC?
     * Why don't the public DCC servers work? Do I need a client-ID?
     * Which ports do I need to open in my firewall?
     * Why does the dccd database grow without bound?
     * The dccd database is corrupt. What should I do?
     * Why did building the DCC fail with a complaint about "Resource
       temporarily unavailable"?
     * Why do my DCC clients including cdcc and dccproc complain
       about "Resource temporarily unavailable"?
     * Why does dccifd or dccm complain about "thread_create()
       failed: 11, try again"?
     * Why doesn't my DCC client pick my local DCC server?
     * If I have a server-ID, do I need a DCC client-ID, or vice
       versa?
     * Why does my DCC server complain about "rejected server-IDs"
       among flooded checksum reports?
     * Why does my server refuse to accept more than 20 operations
       per second?
     * How do I keep strangers from using my DCC server?
     * How can I determine why dccm reported a message as spam or
       with a recipient count of "MANY"?
     * How can I see what checksums my server has heard from its
       clients?
     * Why is mail from my favorite mailing list marked with an X-DCC
       header line that says it is spam?
     * Why are some checksums missing from my X-DCC header lines?
     * Can I use wild cards or regular expressions in DCC white
       lists?
     * How do I white-list mail from a legitimate bulk mailer using
       its name or SMTP headers such as Mailing-List or the Habeas SWE
       headers?
     * Do I need both server and client white lists?
     * How do I maintain client white lists?
     * When the white list file used by dccm or dccproc is changed,
       what must be done to tell the software about the change?
     * Why do legitimate mail messages have X-DCC header lines that
       say they are "bulk"?
     * Are IP address blocks in white lists used by dccproc?
     * Why is dccproc is ignoring env_from white list entries?
     * Why is the DCC server is ignoring env_from white list entries?
     * What if I make a mistake with dccproc -t many and report
       legitimate mail as spam?
     * Can the sendmail "spamfriend" mechanism tell dccm to not check
       mail sent to some addresses?
     * How can I avoid polluting the databases of DCC servers with
       checksums of my mail that is not spam?
     * How many flooding peers does my DCC server need?
     * Do I need to tell the operators of other DCC servers the
       password for controlling my server to turn on flooding?
     * How can I figure out why flooding is not working?
     * Why didn't the RTT reported by the cdcc info operation change
       when my network topology changed?
     * When my clients are configured to use SOCKS, they do not
       realize immediately when a server is down.

   What is the Distributed Checksum Clearinghouse or DCC?
          See the main DCC man page as well as the DCC web pages
          and their mirror

   Do the fuzzy checksums ignore "personalizations"?
          Yes, they ignore many so called "personalizations".

   How much bandwidth, disk space, and computing does the DCC require?
          The UDP packets used by a DCC client to obtain the checksum
          totals from a DCC server for a mail message generally use less
          bandwidth than the DNS queries required to receive the same
          message. A DCC client needs very little disk space.

          Bulk messages are usually logged by DCC clients. On systems
          receiving a lot of mail, the mechanisms for automatically
          creating new log directories every minute, day, or hour can
          keep any single log directory from becoming too large. See the
          dccm and dccproc man pages.

          As of January, 2004, about 100 MBytes/day are exchanged between
          each pair of DCC servers. Each server has 3 or 4 peers. The
          resulting database is about 500 MBytes. However, while
          dbclean is deleting old checksums, there are three copies
          of the database. The DCC clients and server do not need many
          CPU cycles, but the daily executions of dbclean on a system
          with a DCC server require a computer with at least 768 MBytes
          of memory and work better with more.

          DCC servers used by clients handling 100,000 or more messages
          per day need to be larger. Each additional 100,000 messages/day
          need about 100 MBytes of disk space and system memory, given
          the default expiration used by dbclean -e.

          In early 2004, a DCC server prefers at least 768 MBytes of RAM.

   Do I need to run a DCC server?
          A mail system that processes fewer than 100,000 mail messages
          per day uses less of its own bandwidth and the bandwidth of
          other DCC servers by using the public DCC servers. Each mail
          message needs a DCC transaction that requires about 100 bytes,
          and so 100,000 mail messages/day imply about 10 MBytes/day of
          DCC client-server traffic. Each DCC server needs to exchange
          "floods" or streams of checksms with 4 other servers. Each
          flood is currently about 100 MBytes/day for a current total of
          about 400 MBytes/day.

          When normally installed by the included Makefiles, DCC clients
          are configured to use the public DCC servers without any
          additional configuration, except to open firewalls to port

          6277.

          Mail systems that process more than 100,000 mail messages per
          day need local DCC servers connected to the global network of
          DCC servers. The public DCC servers include denial of service
          defenses which ignore requests in excess of about 240,000 per
          day per client.

   What happens to my mail if the DCC crashes?
          When in doubt or trouble, the DCC clients including dccproc
          and dccm deliver mail. They wait only a little while for a
          DCC server to answer before giving up. They then avoid asking a
          server for a while to avoid slowing down mail.

          If the DCC sendmail interface or milter program, dccm, crashes,
          the default parameters in misc/dcc.m4 for the sendmail.cf
          Xdcc line tell sendmail to wait only about 30 seconds before
          giving up and delivering the mail.

          The DCC client code keeps track of the speeds of the servers it
          knows about, and uses the fastest or closest. Every hour or so
          it re-resolves A records and checks the speeds of the servers
          it is not using. When the current server stops working or gets
          significantly slower, the client code switches to a better
          server.

   How do I mark spam without rejecting it?
          Unless given thresholds at which to reject mail, dccm and
          dccproc do not reject mail. When dccm is given a threshold
          by setting DCCM_REJECT_AT in dcc_conf in the DCC home
          directory, DCCM_ARGS can also be set to "-a IGNORE so that
          spam is marked but not rejected.

   Why doesn't the man command find the man pages?
          The nroff source, formated nroff output, and HTML versions of
          the man pages are in the top-level source directory. Formatted
          or nroff source is installed by default somewhere in
          /usr/local/man depending on the target system. It may be
          necessary to add /usr/local/man to the MANPATH environment
          variable. Even with that, SunOS 5.7 sometimes has trouble
          finding them unless man -F is used.

   Must sendmail be used with the DCC?
          While the sendmail milter interface, dccm and the DCC
          program interface or dccifd are the most efficient ways to
          report and check DCC checksums, dccproc is also commonly
          used.

   How can the DCC be used with qmail?
          There are comments about using dccproc with qmail in the
          DCC mailing list archives including Chris Shenton's
          message. See also Chris Shenton's DCC, qmail, and gnus
          page.

   Can the DCC be used with smtpd?
          Yes, dccproc can be used with Obtuse's smtpd. Dave Lugo has
          contributed a shell script to the smtpd-sd project which
          can be used to do DCC checking prior to the end of the SMTP
          DATA command.

   Can the DCC be used with Exim?
          There are comments about using Dccproc with Exim in the
          DCC mailing list archives including these messages:

          + 2002/000203
          + 2002/000254

   Can the DCC be used with SpamAssassin or other spam filters?
          The DCC can be used with SpamAssassin as well as other spam
          and virus filters. Note that it is more efficient to arrange to
          use a DCC client daemon such as dccm to mark passing mail
          and check X-DCC header lines in the filter than to start and
          run dccproc on each message.

          Some commercial virus and spam filters include DCC clients that
          query public DCC servers or DCC servers operated by the filter
          vendor and that "flood" or exchange bulk mail checksums with
          public servers.

   How can the DCC be used with mail user agents?
          Dccproc can be used with any mail user agent that can check
          mail headers. For example, WD Baseley sent a note to the
          DCC mailing list on how to configure Eudora to act on
          X-DCC header lines.

          Bharat Mediratta has developed DeepSix for people using mail
          user agents on UNIX boxes connected remote servers such as
          corporate Exchange servers. See his project on Sourceforge
          as well as his announcement in the DCC mailing list.

   Must I have the root password to use the DCC?
          No, the procmail or sendmail .forward DCC user programs can be
          installed in an individual ~/bin directory. Then cdcc can
          create a private map file used with dccproc -h dir or
          dccproc -m dir/map.

          Also see the DCC installation instructions.

   Why don't the public DCC servers work? Do I need a client-ID?
          The public DCC servers accept requests from clients using the
          anonymous client-ID. Incorrectly configured firewalls often
          cause problems. Traceroute can be used to send UDP packets to
          test for interfering firewalls. See the answer to the
          firewall question below.

   Which ports do I need to open in my firewall?
          DCC traffic is like DNS traffic. You should treat port 6277
          like port 53. Allow outgoing packets to distant UDP port 6277
          and incoming packets from distant UDP port 6277.

          If `dccproc` fails or the command `cdcc info` says no DCC
          servers are answering, you may need to adjust your firewall.

          If you run a DCC server, open incoming connections to local TCP
          port 6277 from your flooding peers, and outgoing connections to
          your flooding peers from your TCP port 6277. Also open UDP port

          6277 to IP addresses 204.152.184.184 and 192.188.61.3 for the
          DCC server status web page.

          See also the discussion of Cisco ACLs at
          http://www.rhyolite.com/anti-spam/dcc/firewall.html.

   Why does the dccd database grow without bound?
          Dbclean should be run about once a day with a script like
          misc/cron-dccd. An entry like misc/crontab can be put
          into the crontab file for the user that runs dccd, such as
          /var/spool/cron/crontabs/root for Solaris.

   The dccd database is corrupt. What should I do?
          Dbclean -R will usually repair a broken DCC server
          database. However, if your server is "flooding" or exchanging
          checksums with other servers, it is often quicker to stop the
          DCC server, delete the dcc_db and dcc_db.hash files,
          run
          Dbclean -N to create empty database files, and the restart
          dccd with the libexec/start-dccd script. When dccd
          starts, it will notice that the database has been purged and
          ask its flooding peers to rewind and retransmit all of their
          bulk checksums.

   Why did building the DCC fail with a complaint about "Resource
          temporarily unavailable"?
          The most common cause of this problem is the same the next
          question, or bugs in the target platform's fcntl() locking on
          NFS file systems. If the DCC home directory will not be NFS
          mounted, it is probably sufficient to run make a second time.

   Why do my DCC clients including cdcc and dccproc complain
          about "Resource temporarily unavailable"?
          The most common cause of such messages is holding a lock on the
          white list file with an editor. However, perhaps your operating
          system has bugs in its implementation of fcntl file locking,
          particularly for the DCC client map file when it is on an
          NFS file system. If so, try configuring, compiling, and
          installing with the --with-bad-locks setting mentioned in
          the installation instructions.

   Why does dccifd or dccm complain about "thread_create() failed: 11,
          try again"?
          The most common cause of "thread_create() failed: 11, try
          again" error messages from dccm and dccifd is a too
          small limit on the maximum number of processes allowed the UID
          running the dccm or dccifd process. The "maxproc" limit should
          be a dozen or so larger than the sum of the queue sizes of dccm
          or dccifd (or both if both are running).

   Why doesn't my DCC client pick my local DCC server?
          The DCC clients including dccm and dccproc pick the
          nearest and fastest server in the list kept in the
          /var/dcc/map file. DCC servers not in that list will not
          be used. That list can be viewed with the cdcc info or
          cdcc RTT operations. Add to the list with cdcc add or
          cdcc load.

          A nearby server that seems slower than a more distant server
          will not be chosen. Note that the anonymous user delay set with
          dccd -u is intended to make a server appear slow to
          "freeloaders." The "RTT +/-" value that can be used with the
          cdcc add and cdcc load operations can be used to
          force DCC clients to prefer or avoid servers except when
          absolutely necessary.

   If I have a server-ID, do I need a DCC client-ID, or vice versa?
          DCC server and client-IDs serve distinct purposes. Servers
          require server-IDs to identify each other in the floods of
          checksums they exchange and to recognize authorized users of
          powerful cdcc operations such as stop. DCC servers require
          client-IDs to identify paying clients that should be given
          quicker service that anonymous clients, to refuse reports from
          anonymous clients, or to refuse even to answer queries from
          anonymous clients.

   Why does my DCC server complain about "rejected server-IDs" among
          flooded checksum reports?
          Redundant paths among DCC servers exchanging or flooding
          reports of checksums would cause duplicate entries in each
          server's database without a mechanism that depends on every DCC
          server having a unique server-ID. Parts of that mechanism
          detect two servers claiming a single server-ID and server-IDs
          that are not listed in the local /var/dcc/ids file.
          Reports supposedly from unknown servers are rejected or ignored
          by the DCC server.

          The ID of every server in the network must be in the file,
          usually without its real password. The sample ids file in
          the DCC source is a good start for a new DCC server in the
          network to which dcc.dcc-servers.net belongs. A current copy of
          that file is also in the online copies of the source including
          that at Rhyolite Software.

          At least one server in every network of DCC servers should use
          an ids file without any extra entries to detect rogue server-ID
          assignments.

   Why does my server refuse to accept more than 20 operations per
          second?
          A common cause of such problems is one of the DCC server's
          defenses against denial of service attacks. A DCC server cannot
          know anything about anonymous clients, or clients using
          client-ID 1 or without a client-ID and matching password from
          the /var/dcc/ids file. As far as your server can know, an
          anonymous client sending many operations is run by an unhappy
          sender of unsolicited bulk mail trying to flood your server
          with a denial of service attack. It is easy to tell your client
          its ID with the cdcc add or load operations.

          The default limits can changed by adding an dccd -R
          argument can be added to DCCD_ARGS in the dcc_conf file in
          the DCC home directory,

   How do I keep strangers from using my DCC server?
          See the dccd -Q and dccd -u options.

   How can I determine why dccm reported a message as spam or with a
          recipient count of "MANY"?
          Dccm is usually configured to log mail with recipient counts
          greater than the -t ,log-thold, as well as mail with some
          conflicts among white list entries. Each log file contains
          a single message, its checksums, its disposition, and other
          information as described in the dccm man page.

          See also the dblist -C command.

   How can I see what checksums my server has heard from its clients?
          The dblist -Hv command displays the contents of the
          database. Look for records with your server-ID with
          dblist -I.

   Why is mail from my favorite mailing list marked with an X-DCC header
          line that says it is spam?
          Sources of solicited bulk mail including mailing lists to which
          you have subscribed should usually be in your DCC client
          white list so that they receive no X-DCC header lines.

   Why are some checksums missing from my X-DCC header lines?
          If the DCC client was not able to compute a checksum for a
          message, it will not ask the server about that checksum and the
          checksum will not appear in the X-DCC header. For example, if
          dccproc is not told and cannot figure out the IP address
          of the source of the message, that checksum will be missing.
          The Fuz1 and Fuz2 checksums cannot be computed for messages
          that are too small, and so will be missing for them. A checksum
          will also be missing if the DCC server is configured to not
          count it.

   How do I maintain client white lists?
          The overall procedure includes monitoring bulk mail in the log
          directories specified with dccproc -l, dccm -l, and
          dccm -U, and adding entries to white list files.

          The global dccm white list file specified with
          dccm -w and the white lists specified with dccproc -w
          are easily maintained with ordinary text editors. Note that
          some text editors including versions of vi lock their files.
          Dccm and dccproc are unable to read white list files while they
          are locked.

          White lists specified with dccm -U are easily maintained
          with ordinary text editors by the system administrator.
          However, it is often better to let individual users deal with
          their own white lists. The DCC source includes sample CGI
          scripts to let individual end-users monitor their private logs
          of bulk mail and their individual white lists. See the
          README file in that directory.

   Can I use wild cards or regular expressions in DCC white lists?
          No, regular expressions cannot be used, because DCC client and
          server white lists are converted to lists of checksums. The
          same basic idea is used for DCC client white lists as for the
          DCC protocol. A DCC client computes the checksums for a
          message, and then looks for those checksums in the local white
          list. Depending on the values associated with those checksums,
          the DCC client asks a DCC server about them.

          There would also be portability difficulties in including
          regular expressions in DCC clients. In other words, consider
          the complications of bundling procmail with the DCC code.

          To use regular expressions with the DCC, consider procmail.
          Procmail is included with many UNIX-like systems. See also the
          Procmail Homepage.

          DCC clients can be configured to white- or blacklist using
          called "substitute" headers. See dccproc -S or
          dccm -S.

          It is also possible to use a sendmail access_db file entries to
          white- or blacklist based on portions of SMTP envelope and
          client IP addresses. For example, an access_db file line of
          "From:example.com OK" can be used to tell dccm white-list all
          mail from SMTP clients in the example.com domain. See the -O
          argument to the misc/hackmc script.

   How do I white-list mail from a legitimate bulk mailer using its name
          or SMTP headers such as Mailing-List headers?
          Start by determining an envelope value or SMTP header that
          distinguishes the bulk mail from a sample message or DCC log
          file. The name of the sending computer is the mail_host value
          in dccm log files. If the distinguishing header or
          envelope value is not among the main DCC white list
          values, then a "substitute" value must be used. An "ok
          substitute ..." line must be added to the white list file and
          the DCC client program must be told with dccproc -S or
          dccm -S. There are example white list entries in the
          sample /var/dcc/whiteclnt file.

   Do I need both server and client white lists?
          The dccd whitelist file is not as useful as the client
          white lists used by dccproc whiteclnt and dccm
          whiteclnt files. Entries in a DCC server's white list apply to
          all clients that use that server, including clients in other
          organizations if permitted. Thus, only very global values are
          appropriate for server white lists. Common entries in server
          white lists include the 127.1 IP address, the IP address ranges
          of the SMTP servers of the organization running the server, and
          well known, unimpeachable mailing lists such as CERT's.

          Client white lists apply only to the stream of mail handled by
          the client. Dccm white lists apply to the mail received by
          the associated sendmail process. Distinct organizations and
          individual users can have very different notions of what bulk
          mail is solicited and what other mail is always unsolicited
          bulk mail.

   When the white list file used by dccm or dccproc is
          changed, what must be done to tell the software the change?
          The DCC clients notice when their whiteclnt files as well as
          included files change and automatically rebuild the
          corresponding .dccw hash table files. Changes to the
          dccd whitelist are not effective until after dbclean
          is run.

          Note that some text editors including versions of vi lock their
          files. Dccm and dccproc are unable to read white list files
          while they are locked.

   Why do legitimate mail messags have X-DCC header lines that say they
          are "bulk"?
          There are several possible causes of such problems. The first
          and most obvious is that the mail is solicited bulk mail and
          that the source needs to be added to your white list.

          Another possible reason is that your individual legitimate mail
          messages have not been marked as spam because their Body or
          Fuz1 checksum counts are small, but that the IP address or
          other checksum counts are large. The IP address checksum count,
          for example, is the total of all reports of addressees for that
          checksum. That total is independent of the other checksums, and
          so counts all reports for all messages with that source IP
          address. A source of legitimate mail that has sent a message
          that was reported as spam by one of its recipients will often
          have the totals for the checksums of its IP address, From
          header, and other values be MANY. This is why it usually does
          not make sense to reject mail based on what the DCC server
          reports for the IP address, From header, and other values that
          are not unique to the message. Only the last Received header
          line, the Message-ID line, and body checksums can be expected
          to be unique and sometimes not the Message-ID and Received
          header lines.

   Why is legitimate mail from someone using qmail marked as spam?
          A common cause for that and similar complaints involves null or
          missing Message-ID header lines. Spam often lacks Message-ID
          lines or has a null or "<>" ID, so rejecting mail with null or
          missing Message-IDs can be an effective filter. DCC clients
          treat missing Message-ID lines as if they were present but
          null. The sample whitecommon white list file in the
          DCC source includes the line:

        many    message-id <>

          Some Mail Transfer Agents violate section 3.6.4 of RFC 2822 and
          do not include Message-ID header lines in mail they send,
          including some combinations of qmail and "sendmail -bs" acting
          as the originating MTA, and qmail by itself when it is
          generates a non-delivery message or "bounce." Solutions to this
          problem include removing that line from your white lists
          or adding lines specifying the From or envelope from values of
          senders of legitimate mail lacking Message-ID header lines.

   Are IP address blocks in white lists used by dccproc?
          Yes, dccproc can white-list mail by the IP address of the
          immediately preceding SMTP client, but only if it knows that IP
          address. Unless the dccproc -a or dccproc -R options
          are used, dccproc does not know the IP address.

   Why is dccproc is ignoring env_from white list entries?
          DCC checksums are of the entire header line or envelope value.
          An entry in the white list file for jsmith@example.com will
          have no effect on mail with an envelope value of
          "J.Smith" jsmith@example.com. The file must contain
          "J.Smith" jsmith@example.com.

          Another common cause for this problem is implied by the fact
          that for an env_from white list entry to have any effect,
          dccproc must be able to find the envelope value in the message
          in a Return-Path header or -f must be used. If your mail
          delivery agent does not add a Return-Path header and you do not
          use dccproc -f, then dccproc cannot know about white or
          blacklist entries for envelope return addresses.

          Note also that dccproc has no white list by default and that
          dccproc -w must be used.

   Why is the DCC server is ignoring env_from white list
          entries.
          Common causes of this problem include sendmail access_db file
          entries and blacklisting entries in the DCC client white
          list. Entries in the sendmail access_db or the dccproc or
          dccm whitelist override the DCC server's advice.

          Note also that it is common for a DCC client to be configured
          to use the current nearest of several DCC servers. If one of
          the DCC servers does not have the entry in its white list, the
          DCC client will occasionally not benefit from it.

   What if I make a mistake with dccproc -t many and report
          legitimate mail as spam?
          It is possible to delete checksums from the distributed DCC
          database with the cdcc delck operation. However, it is not
          worth the trouble. Unless the same (as far as the fuzzy
          checksums are concerned) message is sent again, no one is
          likely to notice the mistake before the report of the message's
          checksums expire from the DCC servers' databases for lack of
          repetition.

   Can the sendmail "spamfriend" mechanism tell dccm to not check
          mail sent to some addresses?
          Sendmail decisions to accept, reject, or discard mail are
          largely independent of the decisions made by dccm. The DCC
          equivalent is to add env_to entries to the dccm white
          list. See the sample whiteclnt file in the DCC source

          However, if your sendmail.cf file sets the dcc_notspam
          macro while processing the envelope, then the message will by
          white-listed. This is related to the dcc_isspam macro used
          by sendmail.cf modified by misc/hackmc -R to tell dccm to
          report blacklisted messages as spam to the DCC server.

   How can I avoid polluting databases of DCC servers with checksums of
          my mail that is not spam?
          Reports of checksums with white list entries in your
          server's database are not flooded to its peers. The checksums
          of messages white-listed with entries in local dccm or
          dccproc white lists are not reported to DCC servers. It is
          good to add entries to DCC server and client white lists
          for localhost, your IP address blocks, and your domains if you
          know that none of your users will ever send spam.

          However, in the common mode in which the DCC is used, no
          checksums of mail are pollution. Checksums of genuinely private
          mail will have target counts of 1 or a small number, and so
          will not be flooded by your server to other servers. Strangers
          will not see your private mail and so will not be able to ask
          any DCC server about the checksums of your private mail. On the
          other hand, the DCC functions best by collecting reports of the
          receipt of bulk mail as soon as possible. That implies that it
          is generally desirable to send reports of all mail to a DCC
          server.

          The DCC flooding protocol does not send checksums with counts
          below a DCC server's bulk threshold to other servers.

   How many flooding peers does my DCC server need?
          A DCC server in a network of many servers should have at least
          three flooding peers to ensure that the failure of a single
          server or network link cannot partition the network. Limiting
          the number the number of peers of any server to four or perhaps
          a few more ensures that no single server is critical to the
          network. To minimize the distances in the network, four peers
          per server seem necessary.

          An organization with more than one server can be viewed as a
          single server by other organizations, with its servers flooding
          each other and external peers spread among its servers. This
          protects the network should the organization suffer large scale
          problems while protecting the organization from single points
          of failure.

   Do I need to tell the operators of other DCC servers the password for
          controlling my server to turn on flooding?
          No, you do not need to and generally should not tell other DCC
          server operators the passwords for controlling your server with
          the cdcc command. Every Inter-server flood of checksums is
          authorized by lines in each server's /var/dcc/flod file
          and authenticated by the password associated with the
          passwd-ID in those lines. The passwd-ID is a
          server-ID defined in the /var/dcc/ids file that
          should generally be used only to authenticate floods of
          checksums.

   How can I figure out why flooding is not working?
          Many DCC server problems can be diagnosed by turning on one or
          more of the tracing modes in the server with the
          cdcc trace operation or by restarting the server with
          dccd -T.

          The cdcc flood list operation displays the current
          flooding peers of a DCC server. Counts of checksum reports sent
          and received to and from a single peer can be displayed with
          cdcc "flood stats ID"

          The positions in the local database of outgoing streams of
          checksums are displayed by the start of dblist -Hv.

   Why didn't the RTT reported by the cdcc info operation change
          when my network topology changed?
          The RTT or round trip time is an average value. Changes in
          network topology, server load, and so forth are not immediately
          reflected in the RTT to avoid switching DCC servers too
          frequently.

   When my clients are configured to use SOCKS, they do not realize
          immediately when a server is down.
          When configured to use SOCKS, DCC clients cannot "connect" to a
          server and so do not receive ICMP errors and must wait for
          timeouts to know the server is not answering.

   This document describes DCC version 1.2.74.

