Network Admin Interview Question and Answers

Q:What is Networking?
Inter connection between the two or more computers is called the networking. Using three types of network are Intranet, Internet and Extranet (Eg. LAN, WAN & MAN)

Q:What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth. Every line has a capacity of transmission of data, The maximum amount of data that can be transferred in a single line is called Bandwidth.

Q:What is VLAN?
VLAN Stand for Virtual Local Area Network. It is a logical grouping of network users and resources connected to administratively defined ports on a switch.
Uses of VLAN are as follows:-

1. It is securied connection.
2. It increases flexibility.
3. It creates separate broadcast domain.

Q:What is CIDR?
CIDR Stands for classless inter domain routing. It helps in preventing the wasting of IP address and nowadays we are facing the shortage of the IP address.So this CIDR helps to prevent the waste of IP address.Shortly IPV6 will come into exist.

Q:What is VLSM?
VLSM stands for Variable length subnet mask, when try to separate a major subnet into minor ones, then that process is called VLSM. We can subnet in various lengths.
Eg: can be separated into and

Q:What is unicast?
Unicast is one type of transmission in which information is sent from one host to another host (i.e Source to Destination). In another words, Unicast transmission is between one-to-one nodes

Unicast ---> A transmission to a single interface card.

Q:What is Multicast?

Multicast is such differ from Unicast. It is another type of transmission or communication in which there may be more than host and the information sent is meant for a set of host.(i.e one source to group of destination

Multicast ---> A transmission to a group of interface cards on the network.

Q:What is Broadcast?

Broadcast is one type of transmission in which information is transfer from just one host but is received by all the host connected to the network. (i.e one source to all destination)

Broadcast ---> A transmission to all interface cards on the network.

Q:What is ACL?
ACL stands of Access Control List, It is packet filtering method, which filter the IP packets based on source and destination address. It is set of rules or condition that permit or deny the ip packets.

Cisco ACLs are divided into types.
1. Standard ACL &
2. Extended ACL.

Standard ACL - Standard IP Access Lists ranging in number from 1 to 99. Standard ACL control the traffic based on the source IP address only.

Extended ACL - Extended IP Access Lists ranging in number from 100 to 199. Extended ACL control the traffic based on the source IP address, destination IP address, source port number and destination port number.

Q:What is CEF?
Cisco Express Forwarding (CEF) is an advanced layer 3 switching technology used mainly in large core networks or the Internet to enhance the overall network performance.

CEF is mainly used to increase packet switching speed by reducing the overhead and delays introduced by other routing techniques. CEF consists of two key components: The Forwarding Information Base (FIB) and adjacencies. The FIB is similar to the routing table generated by multiple routing protocols, maintaining only the next-hop address for a particular IP-route.

The adjacency maintains layer 2 or switching information linked to a particular FIB entry, avoiding the need for an ARP request for each table lookup. There are five types of adjacencies:

1. Null adjacency.
2. Punt adjacency.
3. Glean adjacency.
4. Discard adjacency.
5. Drop adjacency.

Q:What is CDP?
CDP Stand for Cisco Discovery Protocol, It's a Layer 2 protocol and used to check the availability of neighbouring Cisco devices. It can give you all the details of the neighbours. CDP provides network device inventory, connectivity information, and IP next hop information. CDP Version-2 (CDPv2) is the most recent release of the protocol and provides more intelligent device tracking features.

Sending CDP packets every 60 seconds and

Hold time is 180 seconds.

Q:What is SNMP?
The Simple Network Management Protocol (SNMP) is an application layer protocol (Layer 1) that facilitates the exchange of management information between network devices. It is part of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite. SNMP enables network administrators to manage network performance, find and solve network problems, and plan for network growth.

Q:What is RIP and difference between Rip V1 & Rip V2?
RIP Stands for Routing information protocol. It is also called distance vector routing protocol. It is open standard for any vendor use. It uses metric as hop count (max hop count 15) AD 120. It sends periodic update for every 30 sec. It is used for small network.

Rip V1
1. It is a Class full Protocol.
2.Classful Protocol: - Supports networks with same Subnet Mask
3.RIPV1 uses Broadcast Address
4.RIPV1 Universal Broadcast (
5. RIPV1 does not VLSM.
Rip V2
1. It is a Classless Protocol.
2.Classless Protocol: - Supports subnetted networks; It carries the information of   subnet mask
3.RIP V2 uses Multicast Address
4. RIPV2 uses Multicast (
5.RIPV2 supports VLSM

Q:What is EIGRP?
EIGRP stands for Enhanced Interior Gateway Routing Protocol, it is also called balanced hybrid routing protocol or advanced distance vector routing protocol. Hello packets for every 5 sec, hold time 15 sec. It support for VLSM, the multicast address is It maintain neighbour table, topology table & routing table
  1. Neighbour – directly connected neighbour (feasible successor)
  2. Topology – all path reach to destination (feasible successor)
  3. Routing – best path (successor)
DUAL Diffusion update algorithm
  1. Successor is available in routing table
  2. If successor failed means it will take the feasible successor
DUAL Parameter
  1. A.D = Advertised distance (Reported Distance)
  2. F.D = Feasible distance
Reported Distance: The metric for a route advertised by a neighbour
Feasible distance: The distance advertised by a neighbour plus the cost to get to that neighbor

Q:What is OSPF?
Open Shortest Path First (OSPF) is a dynamic routing protocol for use in Internet Protocol (IP) networks. OSPF is designated by the Internet Engineering Task Force (IETF). Specifically, it is a link-state routing protocol and falls into the group of interior gateway protocols, operating within an autonomous system (AS). Unlimited router can be used. CPU usage will be high, to reduce the CPU Usage using area.

Q:What are the areas in OSPF?
• The backbone area, which is also referred to as Area 0. All other areas must connect to the backbone area. Hence, this area is obligatory.

• An ordinary or standard area, which is an area that connects to the backbone (Area 0) and is treated as a separate entity. All routers in a standard area have the same topological database, but their routing tables will be based on the routers position in the standard area and will thus be unique to the router.

• A stub area, which is an area that does not accept external summary routes. A router within a stub area can only see outside the autonomous system if a default route has been configuration for it.

• A totally stubby area, which is similar to a stub area. In this area, the default route must be configured as This type of area is useful for remote sites that have few networks and limited connectivity with the rest of the network and is a Cisco proprietary solution.
• A not so stubby area (NSSA), which is a stub area that can receive external routes but will not propagate those external routes into the backbone area.

Q:What are the network types in OSPF?
1. Non broadcast - This is the default on frame relay networks has a DR/BDR election.  Neighbor command needed to establish adjacency.

2. Broadcast - This is the default on Ethernet/broadcast networks.  Does have DR/BDR election.

3. Point-to-point -  No DR/BDR election.  This one is pretty self explanatory.

4. Point-to-multipoint - Does not have a DR/BDR election. Solves some design issues with the next hop processing for NONBROADCAST.  Treats as a collection of P2P links.

5. Point-to-multipoint non broadcast - Same as P2M but does not use pseudo broadcast.  Must statically define neighbors.

6. Loopback - OSPF treats these as stub hosts. (/32)

Q:What are BGP and their attributes?
The Border Gateway Protocol (BGP) is an inter autonomous system routing protocol. An autonomous system is a network or group of networks under a common administration and with common routing policies. BGP is used to exchange routing information for the Internet and is the protocol used between Internet service providers (ISP). Customer networks, such as universities and corporations, usually employ an Interior Gateway Protocol (IGP) such as RIP or OSPF for the exchange of routing information within their networks. Customers connect to ISPs, and ISPs use BGP to exchange customer and ISP routes. When BGP is used between autonomous systems (AS), the protocol is referred to as External BGP (EBGP). If a service provider is using BGP to exchange routes within an AS, then the protocol is referred to as Interior BGP (IBGP).
BGP Attributes  are
1. Weight                                              5. AS_path
2. Local preference                                 6. Next hop
3. Multi-exit discriminator                         7. Community

Q:What is PPPoE?
Point to Point Protocol over Ethernet (PPPoE) is network protocols that allow data communication between two network entities or points, which supports network layer protocols including IPv4 and IPv6. PPP supports three types of user authentication protocols that provide varying levels of security.
  1. PAP                          2.  CHAP                                3.  EAP
1. Clear text
1. Encrypted
2. Less secure
2. High secure
3. Two way handshake method
3. Three way handshake method
         Auth. Request
         Auth. Acknowledgment

4. No periodic Check up
4. Periodical Check up
Extensible Authentication Protocol (EAP) is most commonly used for authentication on wireless networks

Q:What are the timers for dynamic routing protocol?

60 sec
10 sec
Update timers
30 sec
90 sec

Dead timers
180 sec

Q:What is the AD Value for Dynamic routing protocols?


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