Top 100+ JNCIA Junos Interview Questions

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1. Name few important fields that can be found in an ETHERNET FRAME header?
2. Name the few important fields of an IPv4 Header?
3. You have a requirement where a voice over IP application is being introduced for users to talk to each other over IP networks. Which transport protocol would select for this purpose in order to have latency free VoIP user experience?
4. An Ipv4 address consists of four fields or octets. How many total bits are present in each octet of IPv4 address?
5. TCP is one of the widely used protocol of delivery of data across networks. Describe some of the characteristic of Transmission control protocol?
6. Computer networks work on binary calculations, which of following represents the equivalence for binary value of 11110?
7. Every IP address in any networking device has associated network mask or subnet mask with it. E.g., your computer IP address can be 192.168.1.15. How would you clearly define the purpose or characteristics of subnet mask?
8. RFC 1918 defines a range of IP addressing which are supposed to be used only in private networks and are not to be routed over the internet. Which pools in IPv4 addresses belong to these ranges?
9. In layer 2 networks, the concept of broadcast domain is very crucial in order to communicate without having layer 2 loops and flooding of ARP attacks. Could you illustrate on concept of broadcast domain?
10. You have Subnet mask of 255.255.252.0. How can it be represented in CIDR style?
11. For the reliable delivery of data, we rely on connection oriented transport mechanism like TCP/IP. Mention some of such protocols which work similarly as reliable connection oriented protocols.
12. How many users or hosts can be assigned in the subnet 192.168.1.0/29?
13. What are the main features of IPv6 over IPv4 in general?
14. Mention few application services that are best to be used with UDP rather than TCP?
15. How much is the address space allocated for IPv6 address family? How many possible addresses are there in IPv6 range?
16. Your network administrator has assigned a pool of IP address 192.168.20.0/26 for the IT department. You however need to use one static IP from this pool on one of your server. What is the IP range which comes within the mentioned subnet?
17. How many octets of mac address are called Organizationally Unique identifier or OUI, which relates to the hardware manufacturer?
18. UDP is connection less protocol but is widely used in latency sensitive applications. Which IP protocol number is assigned to UDP?
19. SONET technology is widely used in long haul transmissions with optical networking technology. Routers have sonet-enabled interfaces. What are the main three parts of a SONET end-to-end connectivity?
20. Host-A in same network needs to talk to another host B IP address. Which protocol must play a role to make this communication happen?
21. A simple network switch works on which OSI layer?
22. IPv6 addressing is represented in which number system format?
23. A company has two departments with networks 192.168.1.0/24 and other 192.168.100.0/24. They are connected with their respective layer 2 switches. In order to make communication between them which devices needs to be installed in the network?
24. You are working as network Engineer in an ISP and allocated a large pool by IANA for public addresses as 6.5.5.0/23, and need to further allocate it to your different customers. Which technique can be used to split and large pool of subnet into smaller chunks?
25. Which field in IP header ensures that an IP packet does not loop in the network forever and gets discarded in case of layer 3 loop?
26. Junos architecture ensures the multiplane technology to provide more resiliency in the network. How exactly multiplane architecture is defined in simple terms?
27. Name the few actions that are performed in RE of JUNOS device.
28. A Packet forwarding engine’s sole responsibility is to forward the I/O packets as fast as possible across the router’s interfaces. Name the hardware components of Packet forwarding Engine?
29. Which daemon is responsible for configuring and controlling router’s interfaces?
30. You want to pull the statistics of router’s interfaces both input and output statistics, like errors, counts, traffic rate etc. Which of the following process is going to work to get these statistics?
31. What is the major version number on below Junos software? jbundle-6.5R2.4-domestic-signed.tgz
32. A Junos router received a packet from one interface and after passing through lookup in forwarding table, the packet gets out from another interface. What is such type of traffic called?
33. Which Junos platform series is a dedicated firewall, which can be used from small and medium enterprises to large telecom networks?
34. What is the major advantage of JUNOS for a network engineer who needs to have work on different platforms of JUNOS?
35. You are working as a network engineer and need to know the status of all your networking devices via SNMP server. SNMP server reports that one Junos node is down. You try to ping this node to check if it is really down or any particular link is disconnected. What is such kind of traffic called which is used in troubleshooting?
36. In juniper platforms, there are two main engines handling all sort of traffic coming from one interface and destined towards another network, explain?
37. Which table is populated by routing engine and is used to fast forwarding packets and mainly used in Transit traffic?
38. Name list of exception traffic types in JUNOS OS routing engine RE.
39. Which component of JUNOS OS performs the crucial services like firewall, policing and COS?
40. In below given JUNOS Software package, which one is the revised version? jbundle-5.2R1.9-domestic-signed.tgz
41. You are working as a network engineer in a large enterprise, and on daily basis you have many change management tasks on your JUNOS routers. You are making number of changes and before commit you wish to see the changes about to be performed. Which command in JUNOS would achieve that?
42. Which mode in JUNOS is used to run operational commands for checking and showing interfaces statistics and status?
43. What is the main difference between active configuration and candidate configuration?
44. Network Engineers cannot memorize all commands and keywords, which are useful during configurations and troubleshooting. Which keyword if given on operation mode will give all possible commands on given terminal?
45. In Junos “auto complete” cli commands is very good feature. If there is no other options for particular command then the keyword will be automatically complete on pressing space. However, this feature now annoys you because there is need to give long commands and want to see the shorter format of it. How can you achieve this task?
46. Which JUNOS feature allows engineers to manage, configure and troubleshoot the Junos router on a client by means of web browser using HTTP and HTTPs?
47. NETCONF is an application programming Interface used in Juniper routers to perform which functions by using scripting techniques?
48. Name some of the keywords that are filter options in JUNOS software in using show commands like “show interface | “?
49. You have a task to count the total number of interfaces on your Juniper router. By using filter command, which is closest way to achieve it?
50. You have received a complaint from your customers for a particular service not working since last 2 days at a particular time. As a network operations engineer, you found out that there were some changes made 2 days ago at the same time on one of the JUNOS router. Further investigation reveals the second last commit in JUNOS router. Which command will help you see and compare the changes done in this commit?
51. In Junos CLI, name two types of hierarchy?
52. While configuring JUNOS router, you need to move one-step up the hierarchy. Which keyword would you use to do just that?
53. You are working as a network engineer, and given a task to migrate all the connected interfaces to another router. You quickly need to see the interfaces that are up with services on it. What is the best way to achieve it?
54. Juniper router has many types of interfaces. Your task is to filter the Gigabit Ethernet interfaces. Which filtration technique would accomplish this task?
55. In your corporation, you have been given a critical task to perform some changes on your JUNOS router which may impact some of your critical financial applications. You have made changes in configurations and committed them; however, you receive a call from NOC that some applications have gone offline. What is the immediate action you should do to restore services.
56. You are performing some testing in lab on Juniper device, but now you need to make it ready for the production environment. What 2 methods will bring device to default configuration?
57. You have opened a new Junos device. What is the default root password for this device?
58. You are developing process for network management and monitoring and need to assign separate privilege levels to separate teams based on their type of work. One such team is first Level monitoring operations team. Which privileges class you should assign to the monitoring team?
59. Which types of authentication methods does Junos OS support for accessing Juniper devices?
60. Junos OS supports many types of interfaces; however, they are categorized in three main types. Kindly name the interface types?
61. You are managing a big team of network operations and there are many users who have access to these devices. You have requirement to allow some users with only specific privileges to make changes on certain commands but not the full privileges on devices. What is the best way to achieve this task?
62. You are working remotely and talking to an onsite field engineer. You need your onsite engineer to remove port ge-1/2/4. However, he needs to know exactly where this port is located. How can you tell him in modular approach the exact location of this port?
63. You are asked to erase all the configurations on your JUNOS device to start configuring it from scratch. You have decided to use load factory-default command in cli, which other step you must take to make it work.
64. You have a job to roll out a large green field deployment where you need to make several configurations and need to re-use many of the configuration statements repeatedly on same router. You wish to know some easier way to do it so that you do not have to type all those commands repeatedly. JUNOS has a technique for such tasks to make it easier. Can you name such technique from below list?
65. As a network operations engineer it is very important to archive the configurations periodically in order to retrieve them in case of disaster recovery or in case of troubleshooting to see for any clue in archives of old configurations. Junos allows multiple ways to archive your configurations and push to server, can you explain?
66. As a network operations team lead, your responsibility is to be always prepared for any kind of operations disaster. For this purpose, you want your engineers to have the knowledge of best configurations to load in case of any disaster. JUNOS has special feature to cater this, name the option that best describes this feature.
67. You are troubleshooting an issue and just typed a long command, but now you do not need to press enter rather complete discard it. What is the keyboard shortcut to erase complete command?
68. You are working as network operations engineer, suddenly you suspect the router has high CPU and traffic rates are being increased. You suspect potential routing loop or broadcast attack on your device. In order to see suspected interface you must get to know the live traffic stats. Which command would help to know this information?
69. In order to recover the root password for your Juniper device, what steps you must follow?
70. Which keyboard shortcut takes your cursor to the beginning of your command?
71. You have received a complaint for some users not getting good speed on their systems. You suspect an issue with cabling on physical layer, just to make sure you are checking correctly on suspected interface. Which command will give you detailed information on a particular interface?
72. You have a large data network across the country with many customers. Your basic SNMP server can let you know the up or down status of your network elements across the country. However if there is some degradation in service or performance issues in the network you will not be able to know it from your basic SNMP server. Which Juniper solution can help to know about network performance metrics?
73. You are assigned a task to upgrade JUNOS device. As a best practice, you want to store the current active configuration in local drive. Which command will accomplish this task?
74. You are receiving delay between two ends of a network, having many hops in between. To find out exactly which segment is impacted you need to narrow down the intermediate nodes where the delay is coming from. Which utility will be helpful to find out such information?
75. You have just commissioned new connectivity to a corporate customer. Customer is curious to know the delay and packet loss between his network and ISP. In order to do that you wish to satisfy the customer by showing “zero packet loss” with large size of data. How can you show it to customer on Junos router?
76. Your medium sized enterprise network consists of many routers and switches. You need to ensure that users who are in operations team are only able to access these devices via secure session. Name the method that would do that?
77. You are working in Operations team of a large ISP. Many network engineers work at the same time for configuring new services and troubleshooting. You need to know and maintain the records for all such activities of engineers with timestamps. Which technology would help you do that?
78. In network operations and preventive maintenance, we are always supposed to check basic health of the devices from time to time. Which command will give the environmental information about the Juniper router or switch chassis, including the temperature and information about the fans, power supplies, and Routing Engine?
79. Which command is always considered good practice to validate the active configuration before committing and making it active?
80. Which command will restart the Junos device without shutting it down or cutting its power?
81. Link state routing protocols work on link advertisements from their neighboring routers and so build the network topology from these advertisements. What is the default import and export policy for IS-IS link state routing protocol?
82. You have a large network and you run multiple routing protocols in this network. Some static routes are also configured in the network. As network operations engineer you should know the preference of routes coming from different protocols. Define preference against RIP, OSPF, Directly connected and Static routes.
83. You are supposed to configure a filter where you need to match routes that are equal in prefix length or longer than the prefix length or match prefix. Which route filter match type you will use to do such thing?
84. You have a small network and need to configure OSPF area 0 on all the gigabit Ethernet interfaces i.e. ge-0/0/0. What could be the shortest configuration line to do so?
85. Which are the two mandatory components of firewall filter terms.
86. In Junos platforms, we have concept of routing tables and forwarding tables, explain these in simple terms.
87. You have a gigabit Ethernet interface with two addresses configured on. These are 192.168.20.5/24 and 192.168.20.55/24. You are going to make some ping, which will initiate from this interface. Which IP address will be used as a source address for ping in this case where there are multiple addresses configured on the interface?
88. You need to see a route for a particular network destination 192.168.40.0/24. You noticed that in routing table it is showing two destinations for this route. Based on above show route capture which destination will be preferred and why?
89. Name two important configurable terminating actions of a firewall filter in JUNOS?
90. In BGP, multiple export policies are configured on group level and neighbor levels. In addition, there is global level policy applied. Since we know, most explicit policy will be applied in such case. So which policy is applied before others?
91. You have a medium scale enterprise network with main routing protocol working as OSPF. However at many locations static routes have been used. You need to ensure that static routes become the part of end to end routing and for that purpose; you will redistribute them into OSPF. Write configurations lines mandatory to do that.
92. Which is the only type of route that will take preference over static routes?
93. You need to drop any incoming traffic for a subnet. Using static routes you can use either of “Discard” or “Reject” for this purpose. What is the main difference between these two options in functionality?
94. RIP is a distance vector routing protocol and so it is still widely being used in small-scale enterprises with less number of routers. As a network engineer, you must know the default behavior of RIP. Try to define in simple terms the default policy of RIP?
95. You have a network which has become very large over the time. You are now planning to re design your routing plane all over your network. The main goal will be network summarization and route filtration to minimize the routing table. What policy type will you use to do this task?
96. As shown in above scenario, Router A has two subnets behind its Local Area Network, and Router B has two different subnets behind its LAN. Router A and B are connected directly with point-to-point link and ip addresses are already configured with 192.168.1.0/30 subnet. You are only allowed to use static routes to communicate between LAN of Router A and LAN or Router B. How would you accomplish this?
97. You are assigned to design a new network for your company new office in a separate location. You are supposed to design the best way to optimize the network using best design techniques. Now you need to see if need for static routes is mandatory or should you go for dynamic routing protocols. Why would you use or prefer one from another?
98. In large networks, it is very common for a particular network to be advertised and received from multiple routing protocols. Juniper uses a feature to tie break between multiple routing protocols in such scenarios. Name the feature, which is used for such scenarios.
99. You are suspecting a route is missing or hidden in routing table. There can be multiple reasons for a hidden route in routing table. Name any of the reasons for such behavior?
100. In juniper platforms, which feature you can assign service levels with different delay, jitter (delay variation), and packet loss characteristics to particular applications served by specific traffic flows for congestion management?
101. You have multiple IP addresses configured on one of Juniper router interface. You need to ensure one IP is always to take precedence over the other for all sort of multicast and broadcast packets sourced locally or and sent out to interface. Which keyword will you use while configuring such IP address in such a case?
102. Border Gateway Protocol is one of the largest used protocol in the world, since it is the protocol of the internet routes. As network operations engineer you must understand the default behavior of BGP while exporting the routes. Describes the default BGP export behavior?
103. Below output shows the show route of such router. Identify the default gateway IP address as destination configured in this scenario?
104. In any network, where multiple services are running and WAN links are always running out of capacity, we make use of different techniques to control the impact on different latency sensitive services. One such technique is CoS Name the benefits that contribute to network performance with CoS?
105. In the figure, a user behind Router A with IP address 192.168.1.1 wants to communicate to user behind Router D with IP address 10.1.1.1. Router A has two paths to reach to Router D and eventually to IP address 10.1.1.1. Assuming that there are no static routes in this network, which path will be taken?
106. You want to block any traffic towards network 172.16.1.0/29. Mention the best command to do this task without letting the source knowing about it.
107. Large enterprise networks often run multiple protocols on single router. You need to check the total number of interfaces which are in OSPF areas in you router. Mention the best command to see those interfaces?
108. What is the default preference for Static routes on Juniper platforms?
109. While troubleshooting one issue, you noticed that one route is being learnt from both eBGP and iBGP. Which of them will be preferred and why?
110. Below output shows the routing table of a juniper router. Find and mention the gateway for route 192.168.2.0/24.

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ABOUT THE AUTHOR

Rashmi Bhardwaj

I am here to share my knowledge and experience in the field of networking with the goal being – “The more you share, the more you learn.”

I am a biotechnologist by qualification and a Network Enthusiast by interest. I developed interest in networking being in the company of a passionate Network Professional, my husband.

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