Networking Interview Questions

Network Interview Questions

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What is Network? A Network is an interconnection of devices.

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What is Networking? Networking is the communication between the interconnected devices to share the network resources.

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Types of Networks? LAN, WAN, and MAN.

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LAN i) Operate within a limited geographic Area. ii) Allow multi-access to high bandwidth media. iii) Control the network privately under local admin. iv) Provide full-time connectivity to local services.

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WAN i) Operate over a large geographic Area. ii) Allow access over serial interfaces operating at lower speeds. iii) Provide fulltime and part time connectivity. iv) Connect devices separated over wide, even global Areas.

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What is HUB, SWITCH and Router? A Hub is a device into which can connect all devices on network. So they can communicate together. Hub is a broadcast device. A Switch is a device into which can connect all devices on network. So they can communicate together. Hub is a unicast device. Router is a device, which allows communication possible between two or more different networks present in different or same geographic location.

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What is topology? Topology is type of network connection of a system. Topology is divided into two: physical topology and logical topology. Physical topology: The layout of the physical cabling in a network. Logical topology: The logical path of the signal as it travels through the physical topology in a network.

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NIC Network interface card is an interface between the computer and LAN.

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Internetworking Model

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When networks first came into being, computers could typically communicate only with computers from the same manufacturers. In the late 1970’s, the International Organization for Standardization to break this barrier created the OSI Open system Inter Connection model. The OSI model was helping vendors create interoperable network devices. The OSI model describes how data and network information are communicated from applications on one computer, through the network media, to an application on another computer. OSI Model: Application Layer: It is responsible for providing network services to the users. It is also called as a desktop layer. Services are identified by using port no. Port nos are also called as entry and exit point to the layer. 0 – 1023 are reserved port, 1024 – 65535 open client ports. PDU (Protocol Data Unit) application data: To communicate and exchange information, each layer uses. These holds the control information attached to the data at each layer of the model, which is typically attached to the header of the data field but can also be in the tailor or end of the data field. Presentation Layer: It is responsible for converting for data in standard format. Encoding, Encryption and compression will be done by source presentation layer. Decompression, decryption and decoding done by destination presentation layer. Ex: - Text – ASCII, Graphic – BMP, Audio – WAV, Video – MPEG etc. Session Layer: It is responsible for establishing, maintaining and terminating the session. Session layer using session ID. Ex: - RPC- Remote Procedure call, SQL- Sequence Query Language, NFSNetwork File System. Transport Layer: It is responsible for providing connectivity between endto-end connections. It is also called as Heart of OSI layer.

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Tasks are performed: Identifying services: Transmission Control Protocol (TCP); connection oriented; Acknowledgement; reliable; slower; Port no – 6. It is slower because acknowledgement sent every request. Ex: - HTTP; FTP; SMTP; DNS etc. User Data Protocol (UDP); connection less; no acknowledgement; unreliable; Faster; port no – 17. Ex: - DNS; DHCP; TFTP etc. Multiplex and Demultiplex: Multiplex will be done source layer. Destination layer will do demultiplexing. Segmentation: Before sending data the source PC divided the data into segments because of limitation with network devices. Ex: - MTU = 1500 bytes (Maximum Transmission Unit)

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Sequencing and reassembling: After dividing the data into segments source transport layer will give the sequence no for the segments. After receiving the segments data can put back together on the receiving side exactly as transmitted. Error correction: After receiving the segments the destination transport layer will identifying the missing segments and it will send the request to transport source layer. The source device working with IP only the missing segments transport from the source device. IPX will retransmit the whole message. Flow control: Before sending the data source PC will check with destination PC. How fast destination PC can receive the data by sending the dump packet. It is called as flow-control or windowing. (TCP) Transport Header + Data is called segment. Network Layer: It is responsible for providing best path for data to reach the destination. Logical address works on this layer. Router is a network layer device. It is divided into two parts. Routed Protocol. Ex: - IP, IPX, AppleTalk. Routing Protocol. Ex: - RIP, IGRP, OSPF, and EIGRP. (IP) Network Header + segment = packet | | Source IP Destination IP Data Link Layer: It is divided into two-sub layer. o LLC (Logical Link Control) It talks about WAN protocol Ex: - PPP, HDLC Frame Relay. o MAC (Media Access Control) It talks about physical address. It is a 48-bit address. Ex: - 12 digit Hex. It is also responsible for error detection. o Devices working on DLL are switch, Bridge, NIC. o Error detection will do by destination transport layer. Error correction will do by source Transport layer. DLL Header + Packet + DLL Tailor = frame. | | | Source MAC Destination MAC CRC (Cycle Reluctant check) value - Frame check sequence value Physical Layer: It is responsible for Electrical, mechanical and procedural checks. Data will be converted into binary. Data will be inform of electrical pluses if it is coaxial or twisted pair cable and inform of light if it is fiber optic cable. Ex: - Hubs, Repeaters cables, Modems etc.

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IP Addressing IP Addressing is a logical addressing and works on network layer (Layer 3). They are two Version IPv4 32-bits and IPv6 128-bits. Total IP addressing scheme is divided into 5 classes. Class A, B and C is used for LAN and WAN connectivity. Class D is used for Multicasting. Class E is used for Research and development. Note: Class D and E are used flat address. 127.x.x.x is loop back address and also test for TCP/IP operation.

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What is subnet mask? Subnet mask differentiates network portion and host portion. Subnet mask is been given for host identification of Network ID. Represented with all 1’s in the network portion and with all 0’s in the host portion is called default subnet mask.

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What is Subnetting? Dividing a single network into multiple networks. o Converting Host bits into Network bits. i.e., Converting 0’s to 1’s. o Subnetting is also called as FLSM (Fixed Length Subnet Mask). o Subnetting can be done in three ways. Requirements of Networks. Requirements of Hosts Cisco/Notation. Cisco Three-layered i) Access Layer: Routers which are used by the small organization and also known as Desktop or company layer router. Router Series: 800, 1000, 1600, 1700, and 2500

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ii) Distribution Layer: Routers is used by the ISP’s and is also known as ISP layer Routers. Router Series: 2600, 3200, 3600, and 3700 iii) Core Layer: Routers are used by the Global ISP’s and are also known as Backbone Routers. Router Series: 6400, 7200, 7300, 7400, 7500, 7600, 10000, and 12000. What are the standard port numbers for SMTP, POP3, IMAP4, RPC, LDAP and Global Catalog? SMTP – 25, POP3 – 110, IMAP4 – 143, RPC – 135, LDAP – 389, Global Catalog – 3268 •

What is a default gateway?

The exit-point from one network and entry-way into another network, often the router of the network.

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How do you set a default route on an Cisco router?

ip route 0.0.0.0 0.0.0.0 x.x.x.x [where x.x.x.x represents the destination address] •

Describe the lease process of the DHCP server.

DHCP Server leases the IP addresses to the clients as follows:

DORA D (Discover) : DHCP Client sends a broadcast packets to identify the dhcp server, this packet will contain the source MAC. O (Offer) : Once the packet is received by the DHCP server, the server will send the packet containing Source IP and Source MAC. R (Request) : Client will now contact the DHCP server directly and request for the IP address. A (Acknowledge) : DHCP server will send an ack packet which contains the IP address. •

What is IPv6?

Internet Protocol version 6 (IPv6) is a network layer IP standard used by electronic devices to exchange data across a packet-switched internetwork. It follows IPv4 as the second version of the Internet Protocol to be formally adopted for general use. ip v6 it is a 128 bit size address. This is total 8 octants each octant size is 16 bits separated with “:”, it is in hexa decimal format. These 3 types: 1.

unicast address

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multicast address

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anycast address