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Server Virtualization Concepts , Elements Of Networking Essentials

2.5 Summarize server virtualization concepts, features and considerations

Reasons for virtualization

  • Cost benefits: Virtualization reduces the number of servers you have to run, which means savings on hardware costs and also on the total amount of energy needed to run hardware and provide cooling.

  • Redundancy: Virtualization provides a way to practice redundancy without spending on additional hardware. It means same application run on several servers so if one server fails application can be accessed from another server running same application. This reduce interruption in service.

  • Testing environment: With virtualization, creating an additional server for testing takes a few minutes, and doesn't require any additional hardware. In contrast, buying a new physical server (or keeping extras on hand for testing) is expensive, and installing the operating system and applications can be quite time-consuming. Since existing VMs can be cloned with all operating system configurations and applications, it's a very simple process duplicate a production system to test new patches or a new version of an application.

  • Green initiative : Migrating physical servers over to virtual machines and consolidating them onto far fewer physical servers means lowering monthly power and cooling costs in the data center.

  • Disaster recovery Virtualization provide three important components for disaster recovery. First hardware abstraction capability which means disaster recovery site no longer needs to keep identical hardware on hand to match the production environment, and IT can save money by buying cheaper hardware. Second consolidating servers and third virtualization help automate the fail over when a disaster occur.

2.6 Describe common elements of networking essentials

Subnetting : It is nothing but creating networks within a network. Subnetting allows an organization with a single IP address (Class A /ClassB /ClassC) to have multiple subnetworks, thus allowing several physical networks within the organization.

  • Default subnet mask for Class A network: 255.0.0.0

  • Default subnet mask for Class B network: 255.255.0.0

  • Default subnet mask for Class C network: 255.255.255.0

The directed broadcast should reach all Hosts on the intended network (or subnet, if sub netted). For example, the directed broadcast address for an IP network 196.233.24.15 with default subnet mask is 196.233.24.255. This is arrived by putting all 1s for the host portion of the IP address.

DNS (Domain Name Service) : is used for resolution of domain names to IP addresses. WINS, LMHOSTS is used for resolution of NetBIOS names to IP addresses.

DHCP : Dynamic Host Computer Protocol, which leases IP addresses and other parameters like subnet mask, default gateway to client computers dynamically. You have to assign the IP address for your DHCP server statically. A DHCP server can't assign an IP address to itself. Similarly, some other Servers which need static assignment of IP addresses are your DNS server, WINS server, Default gateway.

Static Addressing : You can request a static IP address it is one IP address for only one customer and is constant. These are more reliable for VOIP, for hosting gaming websites and to use VPN. Another advantage is that because you IP is static that is it will not be assigned to any other you need not worry of your IP getting blacklisted because of some only else sending SPAM.

Dynamic addressing : When DHCP client boots, it sends out a DHCP discover message. All DHCP servers answer with an offer message that includes an address which is available to the client. client machine typically repeats the discover message several times to make sure it hears from all the servers, then eventually chooses one server The currently active DHCP server is configured by hand to handle and reserve IP addresses and the IP configuration information that goes with them. Addresses are made available in an order that permits a client to have the best chance of getting back the same address it was using most recently. IP configuration information gets automatically configured for your client machine by the DHCP server.

VPN : VPN stands for Virtual Private Network. A VPN provides a mechanism to access corporate networks safely using Internet. VPN uses encryption to ensure only authorized user can access the corporate resources. A secure tunnel is created through the public network through which the packets are transported between the remote computer and the corporate network. Vit is used for accessing a corporate network securely from remote locations using public Internet. There are two widely known protocols that can be implemented for enabling VPN communications:

  1. 1. PPTP: PPTP stands for Point to Point Tunneling Protocol. It is a PPTP is pioneered by Microsoft and others is a widely used protocol.

  2. 2. L2TP: L2TP stands for Layer Two (2) Tunneling Protocol. L2TP merges the best features of PPTP and L2F (from Cisco Systems).

  3. PPTP and L2TP protocols together with PPP protocol enable ISPs to operate Virtual Private Networks (VPNs).

VLAN � Virtual Local Area Networks:

  • VLAN derives it's name from the fact that there is only one physical network, but two or more logical networks. A VLAN may be created by any of these methods:

  • VLAN by port association - Membership in a VLAN can be defined based on the ports that belong to the VLAN. For example, in a bridge with four ports, ports 1, 2, and 4 belong to VLAN 1 and port 3 belongs to VLAN 2. The main disadvantage of this method is that it does not allow for user mobility. If a user moves to a different location away from the assigned bridge, the network manager must reconfigure the VLAN

  • VLAN by MAC address association: Here, membership in a VLAN is based on the MAC address of the workstation. The switch tracks the MAC addresses which belong to each VLAN (see Figure4). Since MAC addresses form a part of the workstation's network interface card, when a workstation is moved, no reconfiguration is needed to allow the workstation to remain in the same VLAN. This is unlike Layer 1 VLAN's where membership tables must be reconfigured. The main problem with this method is that VLAN membership must be assigned initially. In networks with thousands of users, this is no easy task. Also, in environments where notebook PC's are used, the MAC address is associated with the docking station and not with the notebook PC. Consequently, when a notebook PC is moved to a different docking station, its VLAN membership must be reconfigured.

  • VLANs by Protocol Type - VLAN membership for Layer 2 VLAN's can also be based on the protocol type field found in the Layer 2 header. For example, VLANs that carry only IP traffic and those that carry only IPX traffic. However this type of VLANs are not popular.

  • VLANs by IP subnet address - Membership is based on the Layer 3 header. The network IP subnet address can be used to classify VLAN membership. Although VLAN membership is based on Layer 3 information, this has nothing to do with network routing and should not be confused with router functions. In this method, IP addresses are used only as a mapping to determine membership in VLAN's. No other processing of IP addresses is done. In Layer 3 VLAN's, users can move their workstations without reconfiguring their network addresses. The only problem is that it generally takes longer to forward packets using Layer 3 information than using MAC addresses. This is the most widely used VLAN type.

DMZ (DeMilitalized Zone) : It is a place separate from the LAN where servers reside that can be reached by users on the Internet. If a company intends to host its own servers to be accessed from public Internet, a DMZ is most preferred solution. The network segment within the DMZ is secured by two firewalls, one interfacing with the public Internet, and the other interfacing the internal corporate network. Thus, a DMZ provides additional layer of security to internal corporate network. The type of servers that are hosted on DMZ may include web servers, email servers, file servers, DNS servers, etc.

Ethernet Types :

  • CAT3: This standard was used in 90's for homes and offices. It can transmit data up to 10Mbps with a possible bandwidth of 16MHz

  • CAT5: It uses either the 10BASE-T or 100BASE-T standard for data transmission Using two cable pairs to signal over copper wire. It provides a minimum of 100MHz of bandwidth.

  • CAT5e: It uses four pairs of copper wire. In addition, the wire pairs are twisted more tightly and are sheathed in heavy-duty shielding to eliminate crosstalk. It is used for 1000BASE-T networks, which carry data at a rate of 1 Gbps.

  • CAT6: It can transmit data up to 10Gbps, has a minimum of 250MHz of bandwidth and specifies cable lengths up to 100 meters with 10/100/1000Mbps transfer, along with 10Gbps over shorter distances. It is made up of four twisted pairs of copper wire, an longitudinal separator separates each of the four pairs of wires from each other

  • CAT 6a: It can operate at a frequency of up to 750 MHz and is even less susceptible to interference and crosstalk CAT6a is the preferred cable for 10GBASE-T Ethernet

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