ATAD #11 – Domain Name System (DNS)

The Domain Name System that dates back from the era of the ARPAnet can be understood as a distributed database (like a “phone book”) for any network that translates hostnames to IP addresses, and also vice versa translation called reverse lookup.

The DNS namespace/data stored in a nameserver is divided into manageable sets of data called zones. Zones contain name and IP address information about one or more parts of a DNS domain. A server that contains all of the information for a zone is the authoritative server for the domain. The namespace information is stored in zone files that may contain directives and resource records. Directives (optional) tell the nameserver to perform tasks or apply special settings to the zone. Resource records (mandatory) define the parameters of the zone and assign identities to individual hosts.

A nameserver can take one or more of the following roles:

master

Stores original and authoritative zone records for a namespace, and answers queries about the namespace from other nameservers.

slave

Answers queries from other nameservers concerning namespaces for which it is considered an authority. However, slave nameservers get their namespace information from master nameservers.

caching-only

Offers name-to-IP resolution services, but is not authoritative for any zones. Answers for all resolutions are cached in memory for a fixed period of time, which is specified by the retrieved zone record as the TTL value.

forwarding

Forwards requests to a specific list of nameservers for name resolution. If none of the specified nameservers can perform the resolution, the resolution fails.

Furthur Reading: BIND,  named.conf, rndc

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ATAD #8 – Package Management Systems

A Software Package is usually a software program that provides some functionality bundled with metadata that contains information about the package. And a Package Management System as defined by wikipedia is a collection of tools to automate the process of installing, upgrading, configuring, and removing software packages from a computer. The package management system is more common in unix and unix-like operating systems to operate with multiple packages. A few significant benefits of such a system are

– maintains a Repository of packages available for the running system (OS and Architecture specific) and resolves dependencies among various packages.
– looks up the repository and automatically downloads the requested packages and its dependencies when installation is triggered.
– can be used to easily upgrade the system to a defined release or level.
– system administrators can create repositories of packages which can be pulled by users, thus allowing easy maintenance of systems across the network and centrally stored packages to reduce memory requirements.

Common Package Management Systems are yum (Yellowdog Update Modifier) that is distributed with Fedora and apt (Advanced Packaging Tool) that’s distributed with Ubuntu.

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ATAD #7 – The network administration tool

If my previous post gave you an opinion that configuring networking on Linux is a head spinning task, im sorry; the Network Administraton Tool that is bundled with most of the newer linux distro is there just to make this task easy for you. You should be able to launch the GUI based tool from the ‘System’ drop down menu and in RedHat the system-config-network command can be used.

The following types of interfaces can be configured using the network administraton tool.
– Ethernet
– ISDN
– modem
– xDSL
– token ring
– CIPE
– wireless devices
– device aliases and profiles

Points worth a note:
– ‘Export’ your original networking configuration before editing them, so you can recover from a mistake by importing back the settings. Most of the network administrator tools provide this option.
– ‘Save‘ your settings after editing and ‘Activate‘ the interface after they are created.
– When interface aliases are configured, DHCP will not work with the interface and its aliases

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ATAD #6 – Specifying Networking Options

The /etc/sysconfig/network-scripts/ contains configuration scripts for each network interface, and its important not to confuse this with the /etc/sysconfig/networking/ directory that is used by the Network Administration Tool (system-config-network) whose contents should _not_ be edited manually. Each NIC has its corresponding configuration file /etc/sysconfig/network-scripts/ifcfg-eth(x) which allows the administrator to control the functioning of each interface individually.

Two or more network interfaces can be coupled to act as one to increase bandwidth and provide redundancy by creating a bonding interface using the bonding kernel module . Bonding options can be specified in the kernel module’s configuration file /etc/modprobe.conf, but however IMHO it seems better organized to use the bonding device’s own configuration file /etc/sysconfig/network-scripts/ifcfg-bond(n) instead.

A nice thing to know while changing the speed or duplex settings is that it requires disabling autonegotiation. This needs to be stated first, as the option entries are order-dependent in the ETHTOOL_OPTS= configuration parameter.

ETHTOOL_OPTS=”autoneg off speed 1000 duplex full”

Furthur reading: ethtool, modprobe.conf

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