Pangkalan Pengetahuan

Overview

This article provides steps to resolve DCC (Distributed Checksum Clearinghouse) server connectivity errors that may appear in mail logs or when checking the status of the dccifd service. This issue typically occurs when the local DCC client cannot establish communication with upstream DCC servers due to network restrictions, DNS resolution failures, or outdated routing maps.

Symptoms

The following error appears in the mail log or during a status check of the dccifd service:

Dec  10 07:50:59 test dccproc[1175]: no working DCC servers dcc1.dcc-servers.net dcc2.dcc-servers.net dcc3.dcc-servers.net ... at 127.0.0.1

Additionally, executing the cdcc info command returns a status indicating zero working servers and unresolved hostnames:

# 12/07/11 09:42:21 EET  /var/lib/dcc/map
# Re-resolve names after 11:31:25  Check RTTs after 09:46:25
# 1 total, 0 working servers
IPv6 on   version=3
 
dcc1.dcc-servers.net,-      RTT+1000 ms  anon
#   undefined name or wrong IP version
 
dcc2.dcc-servers.net,-      RTT+1000 ms  anon
#   undefined name or wrong IP version
 
dcc3.dcc-servers.net,-      RTT+1000 ms  anon
#   undefined name or wrong IP version
 
dcc4.dcc-servers.net,-      RTT+1000 ms  anon
#   undefined name or wrong IP version
 
dcc5.dcc-servers.net,-      RTT+1000 ms  anon
#   undefined name or wrong IP version
 
@,-                         RTT-1000 ms  32768 secretXXX
# *127.0.0.1,-
#      not answering
 
################
# 12/07/11 09:42:21 EET  greylist /var/dcc/map
# Re-resolve names after 11:42:21  Check RTTs after 09:57:21
# 1 total, 0 working servers
# continue not asking greylist server 32 seconds after 1 failures
 
@,-                         Greylist 32768 secret1234567890
# *127.0.0.1,6276
#      not answering

Prerequisites

• Ensure that outbound UDP traffic on port 6277 is permitted through all internal and external firewalls. DCC communication relies exclusively on this port.

Resolution Steps

1. Verify Firewall Configuration: Confirm that outbound UDP traffic on port 6277 is allowed. Blockage of this port will prevent the DCC client from reaching upstream servers.
2. Update the DCC Routing Map: After confirming network connectivity, refresh the local server map by executing the following command:

   # cdcc rtt

3. Verify Resolution: Review the output of the cdcc rtt command. A successful update will display active servers with valid RTT (Round Trip Time) metrics and a count of working servers greater than zero:

   #  cdcc rtt
   # 06/17/24 05:20:09 MDT  /var/lib/dcc/map
   # Re-resolve names after 07:20:04  Check RTTs after 05:35:08
   # 1384.96 ms threshold, 1347.22 ms average    12 total, 11 working servers
   IPv6 on   version=3
   
   dcc1.dcc-servers.net,-      RTT+1000 ms  anon
   #  38.124.232.227,-                                                  ID 1102
   #     100% of 32 requests ok  284.96+1000 ms RTT       200 ms queue wait
   #  72.18.213.52,-                                      x.dcc-servers ID 104
   #     100% of 32 requests ok  349.61+1000 ms RTT       300 ms queue wait
   #  193.30.34.12,-                                     www.nova53.net ID 1205
   #      88% of 32 requests ok  396.41+1000 ms RTT       195 ms queue wait
   
   dcc2.dcc-servers.net,-      RTT+1000 ms  anon
   #  72.18.213.53,-                                      x.dcc-servers ID 104
   #     100% of 32 requests ok  349.63+1000 ms RTT       300 ms queue wait
   #  204.90.71.235,-                                       MGTINTERNET ID 1170
   #     100% of 32 requests ok  286.30+1000 ms RTT       200 ms queue wait
   
   dcc3.dcc-servers.net,-      RTT+1000 ms  anon
   #  72.18.213.49,-                                      x.dcc-servers ID 104
   #     100% of 32 requests ok  349.64+1000 ms RTT       300 ms queue wait
   # *184.23.168.46,-                                             sonic ID 1254
   #     100% of 32 requests ok  239.88+1000 ms RTT       200 ms queue wait
   
   dcc4.dcc-servers.net,-      RTT+1000 ms  anon
   #  137.208.8.63,-                                             wuwien ID 1290
   #     100% of 32 requests ok  372.90+1000 ms RTT       200 ms queue wait
   #  212.223.102.90,-                                                  ID 1480
   #      91% of 32 requests ok  388.08+1000 ms RTT       100 ms queue wait
   
   dcc5.dcc-servers.net,-      RTT+1000 ms  anon
   #  193.30.34.14,-                                     www.nova53.net ID 1207
   #      88% of 32 requests ok  396.31+1000 ms RTT       195 ms queue wait
   #  212.223.15.198,-                                                  ID 1481
   #     100% of 32 requests ok  288.04+1000 ms RTT       100 ms queue wait
   
   @,-                         RTT-1000 ms  32768 secretXXX
   #  127.0.0.1,-                                     
   #      not answering
   
   ################
   # 06/17/24 05:20:09 MDT  greylist /var/lib/dcc/map
   # Re-resolve names after 07:20:08  
   # 1 total, 0 working servers
   # continue not asking greylist server 32 seconds after 1 failures
   
   @,-                         Greylist 32768 secretXXX
   # *127.0.0.1,6276                                  
   #      not answering

Troubleshooting & Workarounds

If the DCC servers remain unreachable after verifying firewall rules and refreshing the routing map, you may temporarily disable the DCC anti-spam plugin via the Warden command-line interface:

// disable the DCC plugin
warden --task=antispam:plugins --DCC=0 --reload=yes

Note: Disabling this plugin will suspend DCC-based spam filtering until it is re-enabled. Contact support if persistent connectivity issues occur after applying these steps.