Networking

Setup and Test Bind DNS Zone File Replication to Slave Servers on CentOS

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Scenario: You are on-boarding/bringing up a new Bind DNS server (say NSHost3 – 198.164.12.103) to replace/upgrade your existing Bind DNS server (NSHost2 – 198.164.12.102) You have installed Bind 9.8 as shown on the new server [root@NSHost3 ~]#  named -vBIND 9.8.2rc1-RedHat-9.8.2-0.47.rc1.el6_8.1[root@NSHost3 ~]# You want to configure NSHost3 as slave server for some of the zones are primarily hosted on NSHost1 (198.164.12.101) in your other Data centre You are NOT running or have allowed the tcp/udp port#53 in your iptables Firewall on both NSHost1 and NSHost3 servers   Implementation: Configuring your new server NSHost3 as slave to NSHost1 server requires updating named.conf […]

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Citrix

FIX: CentOS 6.8 Minimal Install: Device eth0 does not seem to be present, delaying initialization

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Scenario: You are running your CentOS virtual machine on XenServer with a Static IPv4 IP-Address. All of sudden your CentOS system loses network connectivity. Upon checking you notice that none of the Network adapters are detected.  The IP-address assigned gets allocated to other systems on the network. Upon attempting to run command ‘service network restart’, you encounter error message: Bringing up interface eth0: Device eth0 does not seem to be present, delaying initialization. [FAILED] You notice that Same error persists even when you add more NICs to the system Same error persists even when you remove or manually update MAC […]

Networking

Setup or Migrate Postfix SMTP relay server on CentOS 6.5

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Scenario: You have a External SMTP relay host configured on older and physical Linux box which you would like to migrate to CentOS host in a virtualized environment. The older Linux box running on Ubuntu 6.06 + Postfix 2.2.10.  You want to migrate it to a virtual machine running CentOS 6.5 + Postfix 2.6.6. OS and Postfix Version details of existing server: root@NSHost1:~# lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description:    Ubuntu 6.06.2 LTS Release:        6.06 Codename:       dapper root@NSHost1:~# root@NSHost1:~# postconf -d | grep mail_version mail_version = 2.2.10 root@NSHost1:~# OS and Postfix Version details of new server: […]