Redundancy and Traffic Management in a Small Network

Redundancy In a Small Network

Redundancy is another important factor of the network design. Its provide reliability in the network. In a business community, the breakdown of the network can be very costly. So, to maintain reliability in the small network, the redundancy is must be required in the network design. It helps to get rid of single points of network failure. There are several ways to achieve redundancy in the small network.

The network redundancy can be taken by installing standby and alternate network devices e.g router and switches but it can also be taken by installing duplicate network links for important areas within the network. In the case of redundancy, When the primary path is not available, the redundant path can immediately start to make sure minimal downtime and continuity of network services. 

The Small networks normally give a single route in the direction Internet using one or more default gateways. If the gateway fails, the whole network loses connectivity to the Internet. So, in this case, it may be suitable for a small business network to pay for a second service provider as a backup. The figure below illustrates network redundancy. 

Traffic Management

The traffic management is another consideration for network administrators. There are different types of traffic and their behavior in the network design to be considered. The real-time traffic required configuration of router and switches, such as voice and video; in a different way relative to other data traffic. A good network design will categorize traffic according to the priority of traffic; as shown in the below table how traffic is categorized. In the end, to enhance the efficiency of the staff and minimize network downtime is important for a small network to minimize downtime.

 

Voice	High Priority	Real-Time Traffic
Video	High Priority	Real-Time Traffic
SMTP	Medium Priority
Internet Messaging	Normal Priority
TCP	Normal Priority
File Transfer Protocol	Low priority

 

IP Address Planning for Small Network

The IP address planning is very important for implementing a small network. All hosts within the small network should have a unique address. The IP addressing scheme must be planned and documented. The IP addresses should be maintained based on the type of device configure the addresses. The different types of devices that required IP addresses are:-

• Servers


• End devices


• Intermediary devices


• Hosts that are accessible from the Internet

The Figure below illustrates the devices which require IP address Planning to assign an IPv4 address.

Proper planning and documentation of the IP addressing are necessary for helping the network administrator to track device types and troubleshoot. Usually, the network administrator knows the ranges of IP addresses assigned to devices. For examples, if all hosts are assigned the IP address range from 100 to 200 and the servers are assigned an IP address between the range of 220 – 250; so it is easy to identify the traffic by IP address; and it is very useful when troubleshooting the network traffic issues using a protocol analyzer.

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If IP address scheme is documented, the network administrator can easily control access to the resources available on the network. The IP addressing scheme is important for hosts that providing resources to the internal and external network such as e-commerce servers. Without proper planning, the security and accessibility are not possible. If a host has a random address assigned from address range, blocking access to this host is difficult. Different device types should be assigned a logical block of addresses within the address range of the network.

When you are a network administrator and want to set up a small network; If you only have a few computers. You maybe assign your network private IP addresses from the 192.168.0.0 to 192.168.255.255 range. There are sufficient addresses available for a small network. If your computer needs to access the internet, you may require public IP address. The public IP address you must purchase from ISPs.

Small Network Topologies

The small networks topologies and technique is too impotent for network professionals because the majority of businesses are required small networks. The small network's design is generally very simple. Generally, the network topologies contain a single router and one or more switches. The small networks may possibly have access points (possibly built into the router) and also IP phones. As for the requirement of the internet, the small networks usually use only a single WAN connection provided by internet service providers. The internet connection may be in the shape of DSL, cable, or an Ethernet. The figure below display the typical small network.

The small network also requires the same skills which required for managing a larger network. The main work in the small network is maintenance and troubleshooting after one-time installation of equipment. The securing devices and information on the network are important for the network administrator.

Device Selection for a Small Network

The small networks also required planning and design according to the user requirement. Network planning ensures the requirements of the user, cost of the network, and implementation options. For a small network implementation, the type of intermediate devices is very important for the design. For the selection of intermediate devices, there are some important factors that required to be measured.

Type of Intermediate Devices

For the implementation of a small network, the first design considerations are the type of intermediate devices have to use in the network. While selecting intermediate devices, there are some factors that need to be measured

Cost

The cost of intermediate devices is determined by its capacity and features. The capacity of the intermediate device based on the number and types of ports available. The network management capabilities, embedded security technologies, and advanced switching technologies also affect the cost of the devices.

The cable cost also is considered which required to connect all device on the network. The redundancy is another factor which affects the cost of the network.

Ports/Interfaces Speed and Types

The interface and port selection on intermediate devices router or switch) is an important decision. Some computers have built-in 1 Gb/s NICs. 10 Gb/s ports also available on newer computers, workstations, and servers. It is too much expensive; to accommodate increased speed on Layer 2 devices that allow the network to evolve without replacing central devices.

Expandability

Both fixed and modular type of network devices is available. Fixed devices have a fixed number and type of ports or interfaces available which cannot be changed, while modular devices have expansion slots that give the flexibility to add new modules as per requirements. Switches are also available with extra ports for high-speed links.

Operating System Features and Services

The operating system feature usually depends on the version of the operating system, a network device usually support features and services, such as:

• Quality of Service (QoS)


• Security


• Voice over IP (VoIP)


• Dynamic Host Configuration Protocol (DHCP)


• Network Address Translation (NAT)


• Layer 3 switching

Server Message Block (SMB)

The Server Message Block (SMB) is a network protocol that allows the host to share data within the same network. It is share directories, files, printers, and serial ports as easily as if they were on the local computer. It is a request-response protocol and it used TCP port 445 for communication. All the messages of Server Message Block protocol have a common format, which uses a fixed-sized header, with a parameter of variable size and a data component.

The Server Message Block protocol suite is comparatively easy and simple. It includes commands for resource operation that you might perform on a local disk or printer, such as:

• Creating new files and directories


• Deleting files and directories


• Opening and closing files


• Searching for files and directories


• Reading and writing and editing files


• Queuing and dequeueing files in a print spool

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The Server Message Block servers make the file systems and resources available to the clients in the network. The clients make SMB requests for the available resources on the server using the commands and the servers create SMB response messages. The following are the SMB messages types:-

• Initiate, authenticate, and terminate the sessions


• Control access to file and printer


• Allow to send and receive messages using application

The files sharing and printer sharing both are the main services of Microsoft networking. With releasing of Windows 2000, Microsoft changed the original structure for using SMB. Before Windows 2000, the Server Message Block services used a non-TCP/IP protocol to execute name resolution but after windows2000; all Microsoft products use DNS naming, which allows TCP/IP protocols to support SMB resource sharing. The figure below illustrates the SMB protocols connection establishment.

Using Server Message Block, once the connection is established, the user of the client can access the resources on remote end as if the resource is local to the client host.

although SMB was initially created for Windows; now it can also be used by Linux Unix and Mac OSX, using a software called Samba. With using Samba, Linux, Mac, Windows, and Unix computers can share the same files, folders, and printers.

File Transfer Protocol (FTP)

File Transfer Protocol is an another most used and standard Internet protocol for transmitting files between computers on the Internet over TCP/IP connections. It is application layer protocol. It was first created in 1971 to transfer data between a client and a server. To use this protocol, FTP client application is required on a computer that is used to send and receive data from a server running an FTP daemon (FTPd). The FTP is client-server protocols that work on two channels between client and server:

• Command channel for controlling the conversation between host and server


• Data channel for transmitting and receiving files between client and server

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Clients initiate a connection to the servers to manage traffic using port 21, consisting of client command and server replies. After the client command and server replies, the client establishes the second connection to the server for the transfer of actual data using TCP port 20. The connection to port 20 is established every time there is data to be transferred. The figure below illustrates the FTP connection.

The FTP client can download, upload, delete, rename, move and copy data on a server depending upon user rights. A user typically needs to log on to the FTP server, while some servers use anonymous user for some or all of their content available without login.

The File Transfer Protocol sessions work in two modes, passive and active. In active mode, when a client opens a session via a command channel request; the server then open a data connection back to the client and start transferring data. In the passive mode, the server as an alternative uses the command channel to send the client the information it required to open a data channel. Because in the passive mode the client has initiated all connections, it works better across firewalls and NAT.

The FTP client can work via a simple command line interface; with a graphical user interface (GUI) and the Web browsers can also serve as FTP clients.

Dynamic Host Configuration Protocol (DHCP)

Dynamic Host Configuration Protocol (DHCP) is a protocol used to provide fast, automatic, and central management for the allotment of IP addresses within a network. The Dynamic Host Configuration Protocol (DHCP) automates the assigned IP addresses, subnet masks, gateways, and other networking parameters. This is called dynamic or automatic addressing. The alternative to dynamic addressing is static addressing. In the static addressing, the network administrator manually assigns and configures IP addresses on hosts.

When a client device is turned on and connects to the network; the device requests an IP address from a DHCP server; the DHCP server chooses an address from a configured range of addresses called a pool and assigns it to the client device on lease bases.

DHCP is an ideal and efficient system on a larger network to configure IP address settings where client’s changes occurred frequently. New User may arrive and want connection and someone want to leave the network. Static IP address configuration is too difficult in such a larger network.

DHCP addresses are issued to clients on leased bases. When the lease period is expired; the address must be renewed by DHCP if the client is connected to the network. If the client has been powered down or taken off the network; the address is returned to the pool for reuse.

A variety of devices can be as DHCP servers. The DHCP server in most of the networks is generally a local and dedicated PC-based server. The home users DHCP server is usually a local router that connects the home network to the ISP. Several networks use both static and DHCP address settings. The static addressing is used for network devices and DHCP is used for general purpose. The figure below illustrates the types of DHCP servers that can be used.

There are two types of DHCP, DHCPv4 and DHCPv6 both provide similar services for there clients. The main difference between DHCPv4 and DHCPv6 is the gateway, DHCPv6 does not provide a default gateway address. The gateway can only be obtained automatically from the router's Router Advertisement message.

Dynamic Host Configuration Protocol (DHCP) Operation

When device configured for DHCPv4 boots up or connects to the network; the DHCP client sends broadcasts a DHCP discover message to discover any available DHCP server. When DHCP server receive (DHCPDISCOVER) message, it replies with a DHCPOFFER message. The offer message contains the IPv4 address including subnet mask; the IPv4 address of the DNS server, and the IPv4 address of the default gateway. The offer also includes the duration of the lease period.

Incas of multiple DHCP servers exist on the network, and then the client may receive multiple DHCPOFFER messages. So, the client should choose between them, and sends a DHCPREQUEST message. The DHCPREQUEST message identifies the exact server and leases offer that the client is accepting. A client can also request an address that it had previously been allocated by the server and the server should allow the previously used IP address.

Once the offer has been made for the chosen IP address; the device responds to the DHCP server with a DHCPREQUEST packet to accept it; after which the server sends an ACK that's used to confirm that the device has that specific IP address and to define the amount of time that the device can use the address before getting a new one. If the server decides that the device cannot have the IP address, it will send a NACK.

For example, the client requested the IPv4 address, or offered by the server; is still available, the server returns a DHCPACK (DHCP Acknowledge) message that acknowledges to the client that the lease has been finalized. If the offer is no longer valid, then the server responds with a DHCP negative acknowledgment (DHCPNAK) message. If a DHCPNAK message is returned to the client; then the selection process should start again with a new DHCPDISCOVER message from the client. When a client gets a lease, it should be renewed previous to the lease expiration through another DHCPREQUEST message. The DHCP server is responsible to assign are unique IP addresses to the host.

DHCPv6 has the similar set of messages, the messages are SOLICIT, ADVERTISE, INFORMATION REQUEST, and REPLY

Domain Name Service (DNS)

In the network, devices are labeled with numeric numbers called IP addresses to send and receive data over networks. Domain names were created to change the numeric address into a simple, recognizable name. The DNS is short for Domain Name System (or Service or Server). It is a large database which resides on various computers and it contains the names and IP addresses of different hosts on the internet and different domains. It is the Internet's equivalent of a phone book.

The domain name service is an important service because, domain names are easy for people to remember and access a computer, servers, and websites based on IP addresses. The domain name, such as http://fschub.com, are much easier for the humans to remember that its IP address 192.169.80.98.  In case of changing the IP address of http://fschub.com, it is clear to the user because the domain name remains the same. The new address will be simply linked to the existing domain name. The DNS defines an automatic service that matches resource names with the required numeric IP address including queries format, responses, and data. The DNS protocol uses a single format called a message for all types of client queries and server responses, error messages, and the transfer of resource record information bet]. ween servers.

The domain name system is its own complete network. If one DNS server doesn't know how to translate a particular domain name, it asks another DNS, and so on, until the correct IP address is returned. The Figure below illustrates the steps involved in DNS resolution.

DNS Message Format

The DNS server has two types of messages: query and response. The query message contains a header and question records and the response message contains a header, question records, answer records, authoritative records, and additional records.
The DNS server stores names, addresses and some other records to resolve the names.  Some types of records are following:

• A            -   The IPv4 address of An end device


• AAA      -   The IPv6 address record of an end devices


• NS         -   An authoritative name server


• PTR      -   Record contains the name of a node in the DNS namespace.


• SRC      -   Record contains information about a server


• TXT      -   Record contains arbitrary text


• MX       -   A mail exchange record

Whenever a host sends a query for name resolving, the DNS process, first of all, checks its own stored records to resolve the name. If the record is not found in its own stored records, then it forwards the query to other servers to resolve the name. Once a name resolved and returned to the requesting server, the server for the time being stores the IP address in the event that the same name is requested again.  The figure above illustrates that process.

The DNS Client service on Windows PCs also stores subsequently resolved names in memory. The ipconfig /displaydns command displays all subsequently resolved entries that cached in the memory. DNS uses the below message format for all types of client queries and response, error messages and for resource record sharing between DNS servers.

The DNS has two types of messages, query, and response. Both have the same format. The query message consists of a header and the question records and the response message contents of a header, question records, answer records, authoritative records, and additional records as shown in the figure.

Header -The header is an important element for any message because header contains important control fields. In DNS messages, the header section carries several key control flags and is also where we find out which of the additional sections are even being used in the message. The header also states whether the message is a query or a response. The header for both query and response are the same as shown in the figure. The length of the header is 12 bytes.

Questions-The question section contains fields that describe a question to a name server and the question may be query or response. If the message contains a query then this section contains the question expressing the query. If the message is a contain response than this section contains the question sent in the query to which this is the response.

 Answers- The answer section contains resource records that answer the question. If the message contains a non-error response then this section contains the resource record(s) which match the query to which this is the response.

Authority-The authority section contains one or more resource records that point toward an authoritative name server. If the message is an error response then this section may contain resource record(s) identifying DNS servers which can be queried instead.

Additional- the additional records section contains Resource records which relate to the query but are not strictly answers for the question. If the message is a non-error response then this section may contain resource records, which do not match the query but are related to it.

Fully Qualified Domain Name (FQDN)

For understanding the DNS hierarchy It is essential to know about Fully Qualified Domain Name (FQDN).  A fully qualified domain name (FQDN) consists of the hostname and domain name. The hostname are not case sensitive and can also contain alphabetic and numeric letters. An FQDN is the domain name that specifies its accurate site in the DNS hierarchy. It specifies all domain levels including root and top-level domains. The example of FQDN is “mail.fschub.com” where “mail” is the hostname and the “fschub.com” is the domain name.

DNS Hierarchy

The DNS uses a hierarchical system database for resolving name address. DNS uses domain names to form the hierarchy. The DNS hierarchy is comprised of the following five elements:

1) Root Level

2) Top Level Domains

3) Second Level Domains

4) Sub-Domain

5) Host

Root Level

The DNS root zone is the uppermost level in the DNS hierarchy tree. The root name server is server for the root zone. Thes servers contain the information that makes up the root zone, which is the global list of top-level domains.  The root name servers are very important as they are the first step in resolving a domain name. The root name server are the authoritative servers which serve the DNS root zone. These servers contain the global list of the top-level domains. The root servers are operated by 12 different organizations:

• University of Maryland


• VeriSign Global Registry Services


• Cogent Communications


• University of Southern California, Information Sciences Institute


• Internet Systems Consortium, Inc.


• NASA Ames Research Center


• VeriSign Global Registry Services


• US Army Research Lab


• US DoD Network Information Center


• Netnod


• WIDE Project


• RIPE NCC


• ICANN

 Top Level Domains (TLDs)

TLDs are the next level in the DNS hierarchy. There are many TLDs that serve at the moment. As we have seen the TLDs are classified into two subcategories. The different top-level domains represent either the type of organization or the country of origin. Examples of top-level domains are:

• .com     -   A business or industry


• .org       -   A non-profit organization


• .edu      -    Educational Institutions


• .gov      -    Government Intuitions


• .mil      -     Military Groups


• .net      -     Major network Support Centers


• .org      -     Nonprofit Organization and others


• .int       -     International Organization


• .au       -      Australia


• .pk       -      Pakistan


• .us        -      United States

Second Level Domains

Second Level Domain is come after TLDs in the DNS hierarchy. These domain are directly below the TLDs. Second Level domain are an important part  of the DNS. There are no limits of second level domain like the TLDs. If the domain is available anyone can purchase it.

 Sub-domain

The sub-domain is the last level in the DNS servers. It is the part of the main domain. the only domain that is not only a subdomain is the root domain. For example, alfa.example.com and bravo.example.com are subdomains of the example.com domain, which in turn is a sub domain of the com top-level domain (TLD).

This is the DNS hierarchy and elements of the DNS hierarchy. The DNS hierarchy is just like an inverted tree. The figure below illustrates the hierarchy of DNS.

The nslookup Command

The domain name server addresses are important for network device configuration. Generally, the ISPs provide the IP addresses to use for the DNS servers. The host usually requests to connect to a remote device by name; the requesting client queries the name server to resolve the name to IP address.

The operating systems also have a utility called nslookup that give the opportunity to manually query the nameservers to resolve a given host name. The nslookup can also be used to troubleshoot name resolution issues and to verify the current status of the name servers.