Running dcc server cluster

Vernon Schryver
Fri May 29 14:56:49 UTC 2009

> From: Ross West <>

> We're a small ISP looking at implementing DCC, and since our volume of
> mail that would be checked is probably around ~200k we're having to
> setup our own dcc server.  (That in itself isn't an issue.)
> For redundancy's sake, we're looking at doing 2 servers, but within
> the documentation, it talks about either using a single serverid for a
> "close cluster", or running each server with it's own id.

I hope none of the DCC documentation talks about using a single server-ID
for more than one computer.  Both DCC servers and DCC clients depend
on which DCC server is which by ID.  Things break and alarms go off
when two computers share an ID.

The instructions I send to new DCC server installations talk about 
multiple servers when the site is to have more than one.  Basically:

  - Ensure that all of the servers have enough RAM.  You need more than
     3 GByte just for DCC server process and should have more than 4 GByte.
     (That's real memory for a single process and not the kludge that
     lets a 32-bit Intel CPU share more than 4 GBytes among a bunch of 
     smaller than 4 GByte processes.)

  - Don't even consider using the 4+ year old version of the DCC source
      distributed by some outfits including Linux repackagers.

  - Open TCP and UDP port 6277 for all DCC servers to their flooding peers
      and the server status monitor.  The external flooding peers of
      a site should be distributed among its servers.

  - Ensure that all servers have the same password for at least one
      client-ID such as 32768

  - Define DNS CNAMES for each server, such as and

  - Define DNS A RRs containing IP addresses for all servers, such

  - Teach each DCC client about all servers by running
	cdcc "add RTT-1000 ms  32768 SECRET"
      where SECRET is the password for client-ID 32768 in /var/dcc/ids on
      all servers.  That will let the clients balance their loads among
      the servers named by

  - Ensure that the nightly cron jobs run at different times.

Vernon Schryver

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