System Admin Q & A – XI

Ques 1: – What is Open vSwitch?

Ans: – Open vSwitch is a production quality open source software switch designed to be used as a vswitch in virtualized server environments. A vswitch forwards traffic between different VMs on the same physical host and also forwards traffic between VMs and the physical network. Open vSwitch supports standard management interfaces (e.g. sFlow, NetFlow, RSPAN, CLI), and is open to programmatic extension and control using OpenFlow and the OVSDB management protocol.

Open vSwitch as designed to be compatible with modern switching chipsets. This means that it can be ported to existing high-fanout switches allowing the same flexible control of the physical infrastructure as the virtual infrastructure. It also means that Open vSwitch will be able to take advantage of on-NIC switching chipsets as their functionality matures.

Ques 2: – What is Trunk Port ?

Ans: –A Trunk Link, or ‘Trunk’ is a port configured to carry packets for any VLAN. These type of ports are usually found in connections between switches. These links require the ability to carry packets from all available VLANs because VLANs span over multiple switches.

Ques 3: – What virtualization platforms can use Open vSwitch?

Ans: – Open vSwitch can currently run on any Linux-based virtualization platform (kernel 2.6.18 and newer), including: KVM, VirtualBox, Xen, Xen Cloud Platform, XenServer. As of Linux 3.3 it is part of the mainline kernel.
The bulk of the code is written in platform- independent C and is easily ported to other environments.

Ques 4: – What is VLAN and its advantages ?

Ans: – VLAN refers to Virtual Local Area Network is a virtual LAN that extends its functionalities beyond a single LAN. Through VLAN a network is divided into different logical segments known as broadcast domains. The computers in the VLAN acts as they are connected with the same LAN segment even they are located on the different network segments. In the VLAN, computers can move from one location to another and they can still be the part of the same VLAN. VLAN offers many advantages over the traditional local area network.

The main advantages of the VLAN includes high performance, simplified network administration, security, low cost and the creation of the virtual groups to avoid the collision and data loss in the network. VLAN controls the bandwidth allocations and provides the flexibility and ease of work to the users.In the VLAN, the computers do not need to be physically located at the same place. Though it is a logical entity it is created and configured through the software.

Ques 5: – What are VLAN’s Classifications ?

Ans: –VLAN can be classified into the following types.

  • Layer1 VLAN: It is based on the ports that belongs the VLAN.
  • Layer2VLAN: It is based on the MAC address of the computer. Layer2 VLAN is also based on the protocol type.
  • Layer3VLAN: It is based on the layer3 header. The IP address and the subnet mask are used to determine and classify the VLAN membership.
  • High Layer VLAN: The membership of the VLAN is determined by using the service of applications or the combination of both.

Ques 6: – What could DUP mean when using ping?

Ans: – DUP means duplicate will report duplicate and damaged packets. Duplicate packets should never occur, and seem to be caused by inappropriate link-level retransmissions. Duplicates may occur in many situations and are rarely (if ever) a good sign, although the presence of low levels of duplicates may not always be cause for alarm.

Damaged packets are obviously serious cause for alarm and often indicate broken hardware somewhere in the ping packet’s path (in the network or in the hosts).

Ques 7: – What is IP Masquerade ?

Ans: – IP Masquerade is a networking function in Linux similar to the one-to-many (1:Many) NAT (Network Address Translation) servers found in many commercial firewalls and network routers. For example, if a Linux host is connected to the Internet via PPP, Ethernet, etc., the IP Masquerade feature allows other “internal” computers connected to this Linux box (via PPP, Ethernet, etc.) to also reach the Internet as well. Linux IP Masquerading allows for this functionality even though these internal machines don’t have an officially assigned IP address.

 MASQ allows a set of machines to invisibly access the Internet via the MASQ gateway. To other machines on the Internet, the outgoing traffic will appear to be from the IP MASQ Linux server itself. In addition to the added functionality, IP Masquerade provides the foundation to create a HEAVILY secured networking environment. With a well built firewall, breaking the security of a well configured masquerading system and internal LAN should be considerably difficult to accomplish.

Ques 8: – What is GFS2 filesystem ?

Ans: – GFS2 is a shared file system used by Red Hat Cluster node member simultaneously. GFS2
allows all nodes to have direct concurrent access to the same shared block storage. In addition, GFS2 can also be used as a local filesystem. The principle component to allow such access is lock management. GFS2 uses DLM or Distributed Lock Management to achieve this. Also clustered LVM is used to communicate LVM meta data changes across nodes.

Ques 9: – What is fencing in clustering and why it is required ?

Ans: – Fencing is the process of isolating a node of a computer cluster when the former is malfunctioning. Isolating a node means ensuring that I/O can no longer be done from it. Fencing is typically done automatically, by cluster infrastructure such as shared disk file systems, in order to
protect processes from other active nodes modifying the resources during node failures.

Fencing is required because it is impossible to distinguish between a real failure and a
temporary hang. If the malfunctioning node is really down, then it cannot do any
damage, so theoretically no action would be required (it could simply be brought back
into the cluster with the usual join process).

However, because there is a possibility that a malfunctioning node could itself consider the rest of the cluster to be the one that is malfunctioning, a race condition could ensue, and cause data corruption. Instead, the system has to assume the worst scenario and always fence in case of problems

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