Package update failing with "Error while retrieving package. the message was: Name or service not known" error

Issue

• While updating packages using "up2date -u" command, following exception error occurs for scheduled packages
  from RHN:

Error while retrieving package 4Suite-1.0-3.el4_8.1. the message was: Name or service not known"  

• Also following error appears in event log for system profile on RHN:

Client execution returned "Failed: There was a communication error talking to the server" (code 21)