CCNP Job Interview Questions & Answers

CCNP Job Interview Questions & Answere Part 1

Q1. What are three types of LAN traffic?

Ans. Unicasts - intended for one host.

Broadcasts - intended for everyone.

Multicasts - intended for a only a subset or group within an entire network.

Q2. What are unicast frames?

Ans. Unicast frames are the most common type of network traffic. A unicast frame is a frame intended for only one host. The only station that processes this frame is one station that has its own MAC address in the destination portion of packet.

Q3. How do you enable IGRP on a Cisco router?

Ans. The way you enable IGRP on a Cisco router is similar to the way you enable RIP, except you specify IGRP as the protocol and add an autonomous system number. For example:

RouterA(config)# router igrp 10 (10 is the AS number)

RouterA(config-router)# network 192.168.0.0

RouterA(config-router)# network 192.168.1.0

RouterA(config-router)# network 192.168.2.0

Q4. What is Interior Gateway Routing Protocol (IGRP)?

Ans. IGRP is a Cisco proprietary distance vector routing protocol. IGRP has a default hop count of 100 hops, with a maximum hop count of 255. IGRP uses bandwidth and line delay as its default metric, but it can also use reliability, load, and MTU.

Q5. What is the destination address of broadcast frames?

Ans. The destination address of broadcast frames (Layer 2 broadcast addresses) is FF-FF-FF-FF-FF-FF, or all 1s in binary.

Q6. What is the difference between bridges and switches?

Ans. Bridges and switches function the same way; the only difference is in how they are implemented. Bridges are implemented by software and usually have a couple of network ports. Switches are implemented in hardware by ASIC chips and have many ports.

Q7. What is the Spanning-Tree Protocol (STP)?

Ans. STP is a loop-prevention bridge-to-bridge protocol. Its main purpose is to dynamically maintain a loop-free network. It does this by sending out Bridge Protocol Data Units (BPDUs), discovering any loops in the topology, and blocking one or more redundant links.

Q8. In spanning tree, what is a Bridge ID (BID)?

Ans. A BID is an 8-byte field that is composed of the bridge's 6-byte MAC address and a 2-byte bridge priority.

Q9. What is the default bridge priority in a Bridge ID for all Cisco switches?

32,768

Q10. In.In spanning tree, what is path cost?

Ans. Path cost is a calculation to determine the link's bandwidth. It is a value assigned to each port that is based on the port's speed.

Q11. How do bridges pass spanning tree information between themselves?

Ans. Bridges pass STP information using special frame called Bridge Protocol Data Units (BPDUs).

Q12. How often do bridges send BPDUs out active ports?

The default time that bridges send BPDUs out active ports is 2 seconds.

Note: All ports on a switch listen for BPDUs in case there is a topology change.

Q13. What is the STP blocking state?

Ans. When a switch starts, all ports are in the blocking state. This is to prevent any loops in the network. If there is a better path to the root bridge, the port remains in the blocked state. Ports in the blocked state cannot send or receive traffic, but they can receive BPDUs.

Q14. What is the STP listening state?

Ans. Ports transition from a blocked state to a listening state. In this state, no user data is passed. The port only listens for BPDUs. After listening for 15 seconds (if the bridge does not find a better path), the port moves to the next state, the learning state.

Q15. What is the STP learning state?

Ans. In the STP learning state, no user data is being passed. The port quietly builds its bridging table. The default time in the learning state is 15 seconds.

Q16. What is the STP forwarding state?

Ans. After the default time in the learning state is up, the port moves to the forwarding state. In the forwarding state, the port sends and receives data.

Q17. What is STP forward delay?

Ans. The forward delay is the time it takes for a port to move from the listening state to the learning state or from the learning state to the forwarding state. The default time is 30 seconds.

Q18. What is the hello time in STP timers?

Ans. The hello time is the time interval between the sending of BPDUs. The default time is 2 seconds.

Q19. What is the Max Age timer?

Ans.The Max Age timer is how long a bridge stores a BPDU before discarding it. The default time is 20 seconds (ten missed hello intervals).

Q20. What is the default time a port takes to transition from the blocking state to the forwarding state?

Ans.The default time a port takes to transition from the blocking state to the forwarding state is 50 seconds: 20 seconds for Max Age, 15 seconds for listening, and 15 seconds for learning.

Q21. What does STP do when it detects a topology change in the network due to a bridge or link failure?

Ans. If spanning tree detects a change in the network due to a bridge or link failure, at least one bridge interface changes from the blocking state to the forwarding state, or vice versa.

Q22. Describe the central office (CO)?

Ans. The CO is the telco switching facility that connects the customer to the provider's switching network. The CO is sometimes referred to as a point of presence. It is the point where the local loop gains access to the service provider's access lines.

Q23. What is the toll network?

Ans. All the telco switches, COs, and trunk lines inside the WAN provider's network are the toll network.

Q24. What are synchronous links?

Ans. Synchronous links have identical frequencies and contain individual characters encapsulated in control bits, called start/stop bits that designate the beginning and end of each character. Synchronous links try to use the same speed as the other end of a serial link.

Q25. What are Asynchronous links?

Ans. Asynchronous links send digital signals without timing. Asynchronous links agree on the same speed, but there is no check or adjustment of the rates if they are slightly different. Only 1 byte per transfer is sent.

Q26. What are the three layers of the Cisco Hierarchical Model?

Ans. The three layers of the Cisco Hierarchical Model are: 1

the access layer

The distribution layer

The core layer

Q27. How do you enable IGRP on a Cisco router?

Q28. What is flow control, and what are the three methods of implementing it?

Ans. Flow control is the method of controlling the rate at which a computer sends data, thus preventing network congestion. The three methods of implementing flow control are

Buffering

Congestion avoidance

Windowing

Almost certain to be on the exam.

Q29. The IEEE defines what two sublayers of the data link layer?

Ans.The two sublayers of the data link layer are

The Logical Link Control (LLC) sublayer

The Media Access Control (MAC) sublayer

These two sublayers provide physical media independence.

Q30. What are some network devices that operate at the data link layer?

Ans. Bridges and switches are network devices that operate at the data link layer. Both devices filter traffic by MAC addresses.

Q31. The Ethernet and IEEE 802.3 standards define what three physical wiring standards that operate at 10 Mbps?

Ans. These physical wiring standards operate at 10 Mbps:

10Base2

10Base5

10BaseT

Q32. What are broadcast domains?

Ans. A broadcast domain defines a group of devices that receive each others' broadcast messages. As with collisions, the more broadcasts that occur on the network, the slower your network will be. This is because every device that receives a broadcast must process it to see if the broadcast is intended for it.

Q33. What is the difference between a routing protocol and a routed protocol?

Ans. Routing protocols determine how to route traffic to the best location of a routed protocol. Examples of routing protocols are RIP, EIGRP, OSFP, and BGP. Examples of routed protocols are IP and IPX.

Q34. What 3 devices are used to segment a LAN?

Ans. Router

Switch

Bridge

Q35. Besides named access lists, what are the two types of IP access lists?

Ans: Standard Access Lists

Extended Access Lists

Q36. Which layer of the OSI model is responsible for reliable connections?

Ans: The Transport layer of the OSI model is responsible for reliable connections.

Q37  What is the difference between acknowledgments and handshaking?

Ans: Handshaking is used to negotiate the properties of a connection that is being established. Acknowledgments are used to tell the sender that data has been successfully received by the destination during the use of a connection.

Q38  How many VTP modes are there and what are they?

Ans: Three: Server, Client, and Transparent

Q39  What are the two types of Trunk encapsulation protocols?

Ans: IEEE 802.1Q and Cisco’s ISL

Q40  What are the four primary no routable protocols?

Ans: SNA, NetBIOS, DEC LAT, DEC MOP

Q41  What is the difference between TCP and UDP?

Ans: The primary difference between TCP and UDP is that TCP is a connection oriented protocol and UDP is a connectionless protocol.

Q42  What is HSRP?

Ans: HSRP, or the Hot Standby Routing Protocol, is a Cisco proprietary protocol that brings routing functionality to end devices that would otherwise not be capable of taking advantage of redundant network connections. HSRP enables a pair of Cisco routers to work together to present the appearance of a single virtual default-gateway to end devices on a LAN segment.

Q43  What is the difference between a Public IP address and a Private IP address?

Ans: Public address space is a unique address that is assigned to a company. Private address space is not recognized by the Internet and can be used by anyone

within their private network.

Q44  What does AAA stand for?

Ans: Authentication, authorization, and accounting

Q45  The H.323 protocol is used for what?

Ans: H.323 is used for multiservice (multimedia) applications, usually in a Voice Over IP environment.

Q46  What type of routing protocol maintains neighbors?

Ans- Link State

Q47  what is the range of values for administrative distance?

Ans: 0-255

Q48  Describe the difference between unicast, multicast, and broadcast traffic?

Ans: Unicast traffic flows from a single source to a single destination MAC address. Multicast traffic flows from a single source MAC address to many destinations and uses a functional MAC address. Broadcast traffic is from a single source to all devices on the Ethernet segment. This is specified by a destination MAC address of all ones.

Q49  What are the four different Ethernet encapsulation types?

Ans: From the Cisco IPX encapsulation command they are ARPA, NOVELL-ETHER, SAP and SNAP

Q50  What are the three main tasks of a transparent bridge?

Ans: Learning, Forwarding, Filtering

Q51  What type of routing protocol is EIGRP?

Ans: Hybrid

Q52  While troubleshooting a connectivity problem on the network, you issue the ping command from your PC command prompt, but the output shows "request times out." At which OSI layer is this problem associated with?

Ans: The Network Layer

Q53  What algorithm does OSPF use to compute its route table?

Ans: OSPF uses the shortest path first (SPF) algorithm, which is also known as the Dijkstra algorithm.

Q54  What is a stub area?

Ans: A stub area is an area that does not accept routing updates from outside its autonomous system.

Q55  What does the TTL field of an IP packet header do?

Ans: The TTL field indicates the maximum time that a packet can be on the network. Each router that processes this packet decrements the TTL value by 1. If the value reaches zero, the packet is discarded from the network. The purpose of this field is to eliminate the possibility of a packet endlessly traversing the network.

Q56  What is the primary purpose of a LAN?

Ans: The primary purpose of a local-area network is to allow resource sharing. The resources may be devices, applications, or information. Examples of shared resources are files, databases, e-mail, modems, and printers.

Q57: What is a protocol?

Ans: A protocol is an agreed-upon set of rules. In data communications, the rules usually govern a procedure or a format.

Q58: What is the purpose of a MAC protocol?  

Ans: A Media Access Control protocol defines how a given LAN medium is shared, how LAN devices connected to the medium are identified, and how frames transmitted onto the medium are formatted.  

Q59: What is a frame?  

Ans: A frame is a digital "envelope" that provides the information necessary for the delivery of data across a data link. Typical components of a frame are identifiers (addresses) of the source and destination devices on the data link, an indicator of the type of data enclosed in the frame, anderror-checking information.  

Q60: What feature is common to all frame types?  

Ans: A feature common to all frame types is a format for identifying devices on the data link.  

Q61: What is a MAC address or MAC identifier?  

Ans: A Media Access Control address or identifier is a means by which individual devices connected to a data link are uniquely identified for the purpose of delivering data.  

Q62: Why is a MAC address not a true address?  

Ans: An address specifies a location. A MAC address is not a true address because it is permanently associated with the interface of a specific device and moves whenever the device moves. A MAC identifies the device, not the location of the device.  

Q63: What are the three sources of signal degradation on a data link?  

Ans: The three sources of signal degradation on a data link are attenuation, interference, and distortion. Attenuation is a function of the resistance of the medium. Interference is a function of noise entering the medium. Distortion is a function of the reactive characteristics of the medium, which react differently to different frequency components of the signal.  

Q64: What is the purpose of a repeater?  

Ans: A repeater is a device that extends the useful range of a physical medium by reading a degradedsignal and producing a "clean" copy of the signal.  

Q65: What is the purpose of a bridge?  

Ans: A bridge is a device that increases the capacity of a LAN. A bridge divides the data link into segments, forwarding only traffic that is generated on one segment and is destined for another segment. By controlling and limiting the traffic on a data link, more devices may be attached to the LAN.  

Q66: What makes a transparent bridge transparent?  

Ans: A transparent bridge "listens promiscuously" on each of its ports. That is, it examines all frames on all media to which it is attached. It records the source MAC identifiers of the frames, and the ports on which it learns the identifiers, in a bridging table. It can then refer to the table when deciding whether to filter or forward a frame. The bridge is transparent because it performs this learning function independently of the devices that originate the frames. The end devices themselves have no knowledge of the bridge.  

Q67: Name three fundamental differences between LANs and WANs.  

Ans: Three fundamental differences between local-area and wide-area networks are  

     LANs are limited to a small geographic area, such as a single building or small campus.  

     WANs cover a large geographic area, from citywide to worldwide.  

     LANs usually consist entirely of privately owned components. Some components of a  

     WAN, such as a packet switching network or point-to-point serial links, are usually leased  

     from a service provider.  

     A LAN provides high bandwidth at a relatively cheap price. The bandwidth across a WAN  

     is significantly more expensive.  

Q68: What is the purpose of a broadcast MAC identifier? What is the broadcast MAC identifier, in hex and in binary?  

Ans: A broadcast MAC identifier, when used as the destination address of a frame, signifies that the data is for all devices attached to the data link. In binary, the broadcast MAC identifier is all ones. In hex, it is ffff.ffff.ffff.  

Q69: What is the primary similarity between a bridge and a router? What is the primary difference  

     between a bridge and a router?  

Ans: The primary similarity between a bridge and a router is that both devices increase the number of hosts that may be interconnected into a common communications network. The difference is that a bridge works by interconnecting separate segments of a single network, whereas a router  

     interconnects separate networks.  

Q70: What is a packet? What is the primary similarity between a frame and a packet? What is the  

     primary difference between a frame and a packet?  

Ans: A packet is the means by which data is transported from one network to another. The similarity between a frame and a packet is that they both encapsulate data and provide an addressing scheme for delivering the data. The difference between a frame and a packet is that the frame delivers data between two devices sharing a common data link, whereas a packet delivers data across a logical pathway, or route, spanning multiple data links.  

Q71: As a packet progresses across an internetwork, does the source address change?  

Ans: Neither the source nor the destination address of a packet changes as it progresses from the source of the packet to the destination.  

Q72: What is a network address? What is the purpose of each part of a network address?  

Ans: Network addresses are the addresses used in packets. Each network address has a network part, which identifies a particular data link, and a host or node part, which identifies a specific device on the data link identified by the network part.  

Q73: What is the primary difference between a network address and a data link identifier?  

Ans: A packet identifies a device from the perspective of the entire internetwork. A frame identifies a device from the perspective of a single data link. Because the connection between two devices across an internetwork is a logical path, a network address is a logical address. Because the connection between two devices across a data link is a physical path, a data link identifier is a physical address.  

Q74: What are the five layers of the TCP/IP protocol suite? What is the purpose of each layer?  

Ans: The five layers of the TCP/IP protocol suite are the following  

     Physical layer  

     Data link layer  

     Internet (or IP) layer  

     Host-to-host layer  

     Application layer  

Q75: What is the most common IP version presently in use?  

Ans: The most common IP version now in use is version 4.  

Q76: What is fragmentation? What fields of the IP header are used for fragmentation?  

Ans: Routers perform fragmentation when a packet is longer than the maximum packet length  

     (Maximum Transmission Unit, or MTU) supported by a data link onto which the packet must be  

     transmitted. The data within the packet will be broken into fragments, and each fragment will be  

     encapsulated in its own packet. The receiver uses the Identifier and Fragment Offset fields and the  

     MF bit of the Flags field to reassemble the fragments.  

Q77: What is the purpose of the TTL field in the IP header? How does the TTL process work?  

Ans:     The Time to Live (TTL) field prevents "lost" packets from being passed endlessly through the IP internetwork. The field contains an 8-bit integer that is set by the originator of the packet. Each router through which the packet passes will decrement the integer by one. If a router decrements the TTL to zero, it will discard the packet and send an ICMP "time exceeded" error message to the packet's source address.  

Q78: What is the first octet rule?  

Ans: The first octet rule determines the class of an IP address as follows  

     Class A: The first bit of the first octet is always 0.

     Class B: The first two bits of the first octet are always 10.

     Class C: The first three bits of the first octet are always 110.

     Class D: The first four bits of the first octet are always 1110.

     Class E: The first four bits of the first octet are always 1111.

Q79: How are class A, B, and C IP addresses recognized in dotted decimal? How are they recognized inbinary?  

Ans: The A, B, C IP addresses are recognized in dotted decimal and binary as follows  

     Class Binary Range of First Octet Decimal Range of First Octet  

     A 0000000 - 01111110 1 - 126  

     B 10000000 - 10111111 128 - 191  

     C 11000000 - 11011111 192- 223  

Q80: What is an address mask, and how does it work?  

Ans: An IP address mask identifies the network part of an IP address. Each one in the 32-bit mask marks the corresponding bit in the IP address as a network bit. A zero in the mask marks the  

     Corresponding bit in the IP address as a host bit. A Boolean AND is performed in all 32 bits of the address and the mask; in the result, all network bits of the mask will be repeated, and all host bits will be changed to zero.  

Q81: What is a subnet? Why are subnets used in IP environments?  

Ans: A subnet is a sub grouping of a class A, B, or C IP address. Without subletting, the network part of a major class A, B, or C IP address can only identify a single data link. Subnetting uses some of the host bits of a major IP address as network bits, allowing the single major address to be “Subdivided" into multiple network addresses.  

Q82: Why can't a subnet of all zeros or all ones be used in a classful routing environment?  

Ans: A classful routing protocol has no way to differentiate between the all-zeroes subnet and the major IP address, and between the all-ones subnet and the all-hosts, all-subnets broadcast address of the major IP address.  

Q83: What is ARP?  

Ans: ARP, or Address Resolution Protocol, is a function that maps the IP addresses of interfaces on a data link to their corresponding MAC identifiers.  

Q84: What is proxy ARP?  

Ans: Proxy ARP is a function of an IP router. If the router hears an ARP request, and  

     The destination network or subnet is in the router's routing table, and  

     The table indicates that the destination is reachable via a different router interface than the  

     one on which the ARP request was received, The router will respond to the ARP request with its own MAC address.  

Q85: What is a redirect?  

Ans: A redirect is an IP router function. If a device has sent a packet to the router and the router must forward the packet to a next-hop router on the same data link, the router will send a redirect to the originating device. The redirect will inform the device that it can reach the next-hop router directly.  

Q86: What is the essential difference between TCP and UDP?  

Ans: TCP, or Transmission Control Protocol, provides a connection-oriented service over the  

     Connectionless internet layer. UDP, or User Datagram Service, provides a connectionless service.  

Q87: What mechanisms does TCP use to provide connection-oriented service?  

Ans: Correct sequencing is accomplished with sequence numbers. Reliability is accomplished by using checksums, acknowledgments, timers, and retransmissions. Flow control is accomplished by windowing.  

Q88: Instead of ARP, Novell NetWare uses a network address that includes a device's MAC address as the host portion. Why can't IP do this?  

Ans: A MAC identifier is a fixed-length binary integer. If IP used MAC identifiers as the host part of the IP address, subnetting would not be possible because there would be no flexibility in using some of the host bits as network bits.  

Q89: NetWare has a transport layer service similar to TCP called Sequenced Packet Exchange (SPX), but no service similar to UDP. Applications requiring connectionless service directly access the connectionless IPX at the network layer. What purpose does UDP serve by providing aconnectionless service on top of what is already a connectionless service?  

Ans: The only purpose of the UDP header is to add fields for the source and destination port numbers.  

Q90: What information must be stored in the route table?  

Ans: At a minimum, each entry of the routing table must include a destination address and the address of a next-hop router or an indication that the destination address is directly connected.  

Q91: What does it mean when a route table says that an address is variably subnetted?  

Ans: Variably subnetted means that the router knows of more than one subnet mask for subnets of the same major IP address.  

Q92: What are discontiguous subnets?  

Ans: Discontiguous subnets are two or more subnets of a major IP network address that are separated by a different major IP address.  

Q93: What command is used to examine the route table in a Cisco router?  

Ans: show ip route is used to examine the routing table of a Cisco router.  

Q94: What are the two bracketed numbers associated with the non-directly connected routes in the route table?  

Ans: The first bracketed number is the administrative distance of the routing protocol by which the route was learned. The second number is the metric of the route.  

Q95: When static routes are configured to reference an exit interface instead of a next-hop address, in what way will the route table be different?  

Ans: When a static route is configured to reference an exit interface instead of a next-hop address, the destination address will be entered into the routing table as directly connected.  

Q96: What is a summary route? In the context of static routing, how are summary routes useful?  

Ans: A summary route is a single route entry that points to multiple subnets or major IP addresses. In the context of static routes, summary routes can reduce the number of static routes that must be configured.  

Q97: What is an administrative distance?  

Ans: An administrative distance is a rating of preference for a routing protocol or a static route. Every routing protocol and every static route has an administrative distance associated with it. When a router learns of a destination via more than one routing protocol or static route, it will use the route with the lowest administrative distance.  

Q98: What is a floating static route?  

Ans: A floating static route is an alternative route to a destination. The administrative distance is set high enough that the floating static route is used only if a more-preferred route becomes unavailable.  

Q99: What is the difference between equal-cost and unequal-cost load sharing?  

Ans: Equal-cost load sharing distributes traffic equally among multiple paths with equal metrics.  

     Unequal-cost load sharing distributes packets among multiple paths with different metrics. The  

     traffic will be distributed inversely proportional to the cost of the routes.  

Q100: How does the switching mode at an interface affect load sharing?  

Ans: If an interface is fast switched, per destination load sharing is performed. If an interface is process switched, per packet load sharing is performed.

Link to 

CCNP Job Interview Questions & Answers Part 2

CCNP Job Interview Questions & Answers Part 3