Ans :

When protocols are implemented for computer communication, we encounter some
challenges due to the infrastructure and machines used in computer network may not be
compatible and aligned with one another. The concept of Internetworking though, highly
desirable, is not easily achievable. Let us see one simple example to understand the
compatibility problem, any two networks, cannot directly communicate by connecting a
wire between the networks. For example, one network could represent a binary 0 by-5
volts, another by +5 volts. Similarly, one could use a packet size of 128 bytes, whereas
other could use 256 byte packets. The method of acknowledgement or error detection

could be different. There could be many such differences. The incompatibility issues
are handled at two levels:

i) Hardware Issues
At the hardware level, an additional component called router is used to connect
physically distinct networks. A router connects to the network in the same way as any
other computer. Any computer connected to the network has a Network Interface Card
(NIC), which has the address (network id+ host id), hard coded into it. A router is a
device with more than one NICs. Router can connect incompatible networks as it has the
necessary hardware (NIC) and protocols.

ii) Software Issues
The routers must agree about the way information would be transmitted to the
destination computer on a different network, since the information is likely to travel
through different routers, there must be a predefined standard to which routers must
confirm. Packet formats and addressing mechanism used by the networks may differ.
One approach could be to perform conversion and reconversion corresponding to
different networks. But this approach is difficult and cumbersome. Therefore, the
Internet communication follows one protocol suite, the TCP/IP. The basic idea is that it
defines a packet size, routing algorithms, error control, flow control methods
universally.

It would be unwise to club all these features in a single piece of software ─ it would
make it very bulky. Therefore, all these features are logically sub-grouped and then the
sub-groups are further grouped into groups called layers. Each layer has an interface
with the adjacent layers, and performs specific functions.

 

Ans :

Analog	Digital
Signals are records waveforms as they are. Signal occupies the same order of spectrum as the analog data.	Converts analog waveforms into set of numbers and records them. The numbers are converted into voltage stream for representation. In case of binary it is converted in 1’s and 0’s.
In analog systems electronic circuits are used for transformation of signals.	In this transformation is done using logic circuits.
About Noise analog signals are more likely to get affected and results in reducing accuracy	Digital signals are less affected, because noise response are analog in nature
Analog signal is a continuous signal which transmits information as a response to changes in physical phenomenon.	Digital signals are discrete time signals generated by digital modulation.
Data transmission is not of high quality	Data transmission has high quality.
Analog devices are not very precise.	Digital systems are very precise.

 The standard mechanism for electronic mail in the Internet is Simple Mail Transfer

Protocol (SMTP). It provides mail and message exchange between TCP/IP hosts.
SMTP is based on end-to-end delivery i.e., an SMTP client contacts the destination
host’s SMTP server directly for delivering the mail. The destination host’s SMTP
server keeps the mail until the mail has been successfully copied into the recipient’s
SMTP. The SMTP is a connection service based on client-server environment and
runs on port number 25 at the server side as shown in the Figure 8. The various
components of SMTP are:

1) Mail Transfer Agent (MTA)
2) User Agent (UA)

 The Dynamic Domain Name System (DDNS) is a protocol that defines extensions to

the DNS in order to enable the DNS servers to accept the requests to add, update and
delete entries in the DNS database dynamically. Because DDNS offers a functional
superset to existing DNS servers, a DDNS server can serve both static and dynamic
domains at the same time. Rather than allowing any host to update its DNS records,
the secure version of DDNS uses public key security and digital signatures to
authenticate update requests from DDNS hosts.

Three common utilities for querying name servers are provided with many DNS
implementations:

1) Host obtains an IP address associated with a host name or a host name associated
with an IP address.

2) Nslookup allows you to locate information about network nodes, examine the
contents of a name server database and establish the accessibility of name servers.

3) Hig allows you to exercise name servers, gather large volumes of domain name
information, and execute simple domain name queries. DIG stands for Domain
Internet Groper.

The following RFCs define the Domain Name System standard and the information
kept in the system:

1) RFC 1032 – Domain Administrator’s Guide
2) RFC 1033 – Domain Administrator Operations Guide
3) RFC 1034 – Domain Names – Concepts and Facilities
4) RFC 1035 – Domain Names – Implementation and Specification
5) RFC 1101 – DNS Encoding of Networks Names and Other Types.

 Ans :

The concept of mapping a domain name to an IP address and vice-versa is known as
resolution process. The resolution process is basically a client server platform.
Whenever a user needs to map an address to a domain or vice-versa, the DNS calls a
client program called resolver. The resolver subsequently contacts the nearest DNS
server (name server) with a request. In case the server has the desired information, it
replies back with the results. Otherwise it suggests the resolver to other domain
servers or asks other servers to provide the desired information. The resolver, after
receiving the results asserts the information and thereafter delivers the desired
information to the specific host process. The steps followed in the resolution are
below

1) The user program issues a request such as the gethostbyname( ) system call. (This
particular call is used to ask for the IP address of a host by passing the host
name as a parameter).

2) The resolver formulates a query to the name server.

3) The name server checks to see if the answer is in its local authoritative database
or cache, and if so, returns it to the client. Otherwise, it will query other available
name server(s), starting down from the root of the DNS tree or as high up the tree
as possible.

4) The user program will finally be given a corresponding IP address (or host name,
depending on the query) or an error if the query could not be answered.
As the resolution process is carried out with the help of queries, these domain name
request queries can be one of two types: recursive or iterative. A flag bit in the
domain name query specifies whether the client desires a recursive query, and a flag
bit in the response specifies whether the server supports recursive queries. A
recursive query requests that the server should itself issue a query to determine the
requested information and return the complete answer to the client. However, an
iterative query means that the name server should return what information it has
available and also a list of additional servers for the client to contact to complete the
query.

The concept of caching is also utilized in DNS. Whenever a name-server receives a
request from a client, the name server subsequently sends the query to other servers.
Later on, when it receives the response, it first stores this information in its own cache
memory before sending the desired information to the client. Now onwards, if any
client desires the same information, first the name-server can simply check its cache
memory and resolve the query. However, such a response is designated as nonauthoritative. The domain name responses from the name server can be one of two
types: authoritative and non-authoritative.

 The hierarchical system of domain names in Internet has been broadly classified into

three categories:

1. Generic domain names
2. Country based domain names
3. Inverse domains
   
   

The three-character top-level names are called the generic domains or the
organizational domains. The generic domain defines registered hosts in accordance
with their behavior for example, yahoo.com uses ‘com’ as top level name as it
signifies that yahoo is a commercial organization. Table 1 shows some of the top-level domains of today’s Internet domain hierarchy.

Domain  Name	Meaning
Com	Commercial organizations
Gov	Government institutions
Org	Non-profit organizations
Mil	Military groups
Edu	Educational institutions
Net	Major network support centers
Int	International organizations

There are also top-level domains named for each of the ISO 3166 international 2-
character country codes (e.g., zw for Zimbabwe). These are called the country
domains. Many countries have their own second-level domains underneath, which
parallel the generic top-level domains.

As it is a simple matter in principle to search the database for an IP address with its
symbolic name (because of the hierarchical structure), the reverse process cannot
follow the hierarchy. Therefore, there is another namespace for the reverse mapping
called Inverse domain. The information about the inverse domain is always stored in
the domain “in-addr.arpa”. Here, the IP addresses are stored in a hierarchical form
such that each level of the tree depicts 8 bits of information of IP address. However,
since domain names have the least significant parts of the name first, but dotted
decimal format has the most significant bytes first, the dotted decimal address is
shown in reverse order. For example, the domain in the domain name system
corresponding to the IP address 171.10.1.2 is 2.1.10.171.in-addr.arpa. The above
mapping is carried out by using a special kind of query called inverse pointer query.

 The following is the step by step procedure to configure a Samba Server

1. Server IP address is xxx.xxx.0.254 and machine name is Server1
2. Windows machine IP address is xxx.xxx.0.2 and machine name is client2
3. Firewall Should be disabled.
   

chkconfig iptables off

service iptables stop

chkconfig ip6tables off

service ip6tables stop

4. To check if all rpms required for samba are installed or not.

              #rpm –qa | grep samba, then it displays the following
             Samba-<version-name>
             Samba-common-<version-name>
             Samba-client-<version-name>
             System-config-samba-<version-name>

5. If not, install it using
                #rpm –ivh samba

6. Copy the original configuration file as smb.conf.bck
               #cp /etc/samba/smb.conf /etc/samba.conf.bck
              (This will keep a backup copy of your configuration file.)

7. Now edit the configuration file
              #vi /etc/samba/smb.conf

8. To share home directory edit this part of /etc/samba/smb.conf

  [homes]

            comment=Home directories
            browseable =no
            writable=yes

9. To share printer edit this part of /etc/samba/smb.conf

  [printers]

           comment = All printers
           path = /var/spool/samba
           browseable = no

10.To configure share called IHNCSHARE edit this part of /etc/samba/smb.conf
[IHNC’s share]
comment = Testing Samba Server
path = /samba
valid users = user1, user2

11. Save the file with wq command

12. To check your configuration file type testparm
#testparm

13. Create two samba users user1 and user2
useradd user1
useradd user2

14. Create smbpassword for both the users
smbpasswd –a user1
smbpasswd –a user2

15. Now you stop/start the samba services

service smb stop
service smb start

16. To see what is shared from your server through samba for a particular user

smbclient -L Server1 –U user1 or smbclient –L //xxx.xxx.0.1 –U user1

17. To see what is shared for a particular host

smbclient –L mac2

18. Now, permanently make samba server on
    #chkconfig smb on