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9 followers study24x7 04 Feb 2019 11:44 AM study24x7 study24x7

A DHCP Server is a network server that automatically provides and assigns IP addresses, default gateways and other network parameters to client devices. It relies on the standard protocol known as Dynamic Host Configuration Protocol or DHCP to respond to broadcast queries by clients. A DHCP server automatically sends the required network parameters for clients to properly communicate on the network. Without it, the network administrator has to manually set up every client that joins the network, which can be cumbersome, especially in large networks. DHCP servers usually assign each client with a unique dynamic IP address, which changes when the client’s lease for that IP address has expired. When to use a router/switch as your DHCP ServerThere are many enterprise companies who are still using DHCP for IPv4 on their routers/switches.  This is typically done by the network administrator who needs to get a DHCP capability up and running quickly but does not have access to a DHCP server. Most routers/switches have the ability to provide the following DHCP server support: a DHCP client and obtain an interface IPv4 address from an upstream DHCP servicea DHCP relay and forward UDP DHCP messages from clients on a LAN to and from a DHCP servera DHCP server whereby the router/switch services DHCP requests directly. However, there are limitations to using a router/switch as a DHCP serverRunning a DHCP server on a router/switch consumes resources on the network device.  These DHCP packets are handled in software (not hardware accelerated forwarding).  The resources required make this practice not suitable for a network with a large number (> 150) of DHCP clients.Does not support dynamic DNS.  The router/switch DHCP server cannot create an entry into DNS on behalf of the client based on the IPv4 address that was leased to the client.No ability to e asily manage the scope and see the current DHCP bindings and leases across multiple routers.  Administrator must log into the switch/router individually to get information about DHCP bindings.No high availability or redundancy of the DHCP bindings.  This could cause problems if the current DHCP server and default gateway fails.It is more difficult to configure DHCP options on router/switch platform.The DHCP service running on a router/switch is not integrated with IP address management (IPAM) for address tracking and scope utilization or security forensics. The Benefits of a dedicated DHCP ServerA better approach than trying to use DHCP on your router/switch is to use a centralized DHCP server. This is particularly true for network environments that require support of both DHCP for IPv4 and DHCP for IPv6 at the same time.  Virtually all DHCP server vendors support both protocols so you can use the same management interface for IPv4 and IPv6.  There are several benefits that make it advantageous for an enterprise to use DHCPv6. Having a DHCPv6 server that is integrated into your IP Address Management (IPAM) system for IPv6 gives visibility to the IPv6-enabled client nodes.You also would want this same functionality for IPv4.  As IPv4 address space becomes increasingly constrained, you will want to keep track of your DHCP scopes and determine if your lease time is adequate with the plethora of BYOD systems joining your networked environment.DHCP servers provide logging and management interfaces that aid administrators manage their IP address scopes.  Your organization will want an accounting of what is on your network regardless of IP version being used.DHCP servers can provide redundancy and high availability.  If one DHCP server were to fail, the clients will preserve their current IP addresses and not cause an interruption for the end-nodes.Organizations will prefer a DHCPv6 server that has been tried and tested.  For example, The Infoblox DHCPv6 server has been certified as “IPv6 Ready” by the USGv6 certification laboratory. Organizations that are beginning to implement IPv6 should migrate DHCP for IPv4 scope off the routers/switches and put them on a robust DHCP server infrastructure. This change will also mean that your organization would want to have DHCP operate the same for both protocols.  Enterprise organizations will want to take advantage of the centralized dual-protocol DHCP server to provide IPv4 and IPv6 addresses to client devices.   

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9 followers study24x7 19 Jan 2019 02:28 PM study24x7 study24x7

Domain Name System:--
DNS (Domain Name System), also known as a nameserver, is a network system that associates host names with their respective IP addresses. For users, this has the advantage that they can refer to machines on the network by names that are usually easier to remember than the numerical network addresses. For system administrators, using the nameserver allows them to change the IP address for a host without ever affecting the name-based queries, or to decide which machines handle these queries.

DNS is usually implemented using one or more centralized servers that are authoritative for certain domains. When a client host requests information from a nameserver, it usually connects to port 53. The nameserver then attempts to resolve the name requested. If it does not have an authoritative answer, or does not already have the answer cached from an earlier query, it queries other nameservers, called root nameservers, to determine which nameservers are authoritative for the name in question, and then queries them to get the requested name.

In a DNS server such as BIND (Berkeley Internet Name Domain), all information is stored in basic data elements called resource records (RR). The resource record is usually a fully qualified domain name (FQDN) of a host, and is broken down into multiple sections organized into a tree-like hierarchy. This hierarchy consists of a main trunk, primary branches, secondary branches, and so on.

Each level of the hierarchy is divided by a period (that is, .). In Example 17.1, “A simple resource record”, com defines the top-level domain, example its subdomain, and sales the subdomain of example. In this case, bob identifies a resource record that is part of the domain. With the exception of the part furthest to the left (that is, bob), each of these sections is called a zone and defines a specific namespace.

Zones are defined on authoritative nameservers through the use of zone files, which contain definitions of the resource records in each zone. Zone files are stored on primary nameservers (also called master nameservers), where changes are made to the files, and secondary nameservers (also called slave nameservers), which receive zone definitions from the primary nameservers. Both primary and secondary nameservers are authoritative for the zone and look the same to clients. Depending on the configuration, any nameserver can also serve as a primary or secondary server for multiple zones at the same time.
There are two nameserver configuration types:
authoritativeAuthoritative nameservers answer to resource records that are part of their zones only. This category includes both primary (master) and secondary (slave) nameservers.

recursiveRecursive nameservers offer resolution services, but they are not authoritative for any zone. Answers for all resolutions are cached in a memory for a fixed period of time, which is specified by the retrieved resource record.

Although a nameserver can be both authoritative and recursive at the same time, it is recommended not to combine the configuration types. To be able to perform their work, authoritative servers should be available to all clients all the time. On the other hand, since the recursive lookup takes far more time than authoritative responses, recursive servers should be available to a restricted number of clients only, otherwise, they are prone to distributed denial of service (DDoS) attacks.

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