Top 50 Router Interview Questions You Must Prepare 04.Dec.2022

Tracert or traceroute depending on the operating system allows you to see exactly what routers you touch as you move along the chain of connections to your final destination. If you end up with a problem where you can't connect or can't ping your final destination, a tracert can help in that regard as you can tell exactly where the chain of connections stop. With this information, you can contact the correct people- whether it be your own firewall, your ISP, your destination's ISP or somewhere in the middle. Tracert, like ping, uses the ICMP protocol but also has the ability to use the first step of the TCP three-way handshake to send out SYN requests for a response.

A Firewall put simply keeps stuff from here talking to stuff over there. Firewalls exist in many different possible configurations with both hardware and software options as well as network and host varieties. Most of the general user base had their first introduction to Firewalls when Windows XP SP2 came along with Windows Firewall installed. This came with a lot of headaches, but to Microsoft's credit it did a lot of good things. Over the years it has improved a great deal and while there are still many options that go above and beyond what it does, what Windows Firewall accomplishes it does very well. Enhanced server-grade versions have been released as well, and have a great deal of customization available to the admin.

If you did any multiplayer PC gaming in the 90s and early 2000s, you likely knew of the IPX protocol as 'the one that actually works'. IPX or Internetwork Packet Exchange was an extremely lightweight protocol, which as a result for the limits of computers of the age was a very good thing. A competitor to TCP/IP, it functions very well in small networks and didn't require elements like DHCP and required little to no configuration, but does not scale well for applications like the Internet. As a result, it fell by the wayside and is now not a required protocol for most elements.

ipconfig is one of the primary network connection troubleshooting and information tools available for Windows Operating Systems. It allows the user to see what the current information is, force a release of those settings if set by DHCP, force a new request for a DHCP lease, and clear out the local DNS cache among other functions it is able to handle. ifconfig is a similar utility for Unix/Linux systems that while at first glance seems to be identical, it actually isn't. It does allow for very quick (and thorough) access to network connection information, it does not allow for the DHCP functions that ipconfig does. These functions in fact are handled by a separate service/daemon called dhcpd.

A print server can refer to two different options- an actual server that shares out many different printers from a central administration point, or a small dedicated box that allows a legacy printer to connect to a network jack. A network attached printer on the other hand has a network card built into it, and thus has no need for the latter option. It can still benefit from the former however, as network attached printers are extremely useful in a corporate environment since they do not require the printer to be connected directly to a single user's system.

The simple answer is that Multimode is cheaper but can't transmit as far. Single Mode has a smaller core (the part that handles light) than Multimode, but is better at keeping the light intact. This allows it to travel greater distances and at higher bandwidths than Multimode. The problem is that the requirements for Single Mode are very specific and as a result it usually is more expensive than Multimode. Therefore for applications, you will usually see Multimode in the datacenter with Single Mode for long-haul connections.

A subnet mask tells the network how big it is. When an address is inside the mask, it will be handled internally as a part of the local network. When it is outside, it will be handled differently as it is not part of the local network. The proper use and calculation of a subnet mask can be a great benefit when designing a network as well as for gauging future growth.

For general VoIP set up we require the following things:

  • Broadband connection
  • VoIP phone
  • Nexton soft-switches
  • Router
  • Audiocodec
  • Astric server

If you were to ask a Microsoft Sales Rep this question, they would no doubt have hundreds of tweaks and performance boosts from system to system. In reality however there are two main differences between the Windows Home edition and Windows Professional: Joining a domain and built-in encryption. Both features are active in Professional only, as joining a domain is nearly a mandatory requirement for businesses. EFS (Encrypted File System) in and its successor Bitlocker are both also only present in Pro. While there are workarounds for both of these items, they do present a nice quality-of-life boost as well as allow easier standardization across multiple systems. That being said, the jump from Windows Pro to Windows Server is a monumental paradigm shift.

While we could go through all of the bells and whistles of what makes Windows Server…Windows Server, it can be summed up very briefly as this: Windows Home and Pro are designed to connect outwards by default and are optimized as such. Windows Server is designed to have other objects connect to it, and as a result it is optimized severely for this purpose. Windows Server 2012 has taken this to a new extreme with being able to perform an installation style very similar to that of a Unix/Linux system with no GUI whatsoever. As a result, they claim that the attack vector of the Operating System has been reduced massively (when installing it in that mode)

ICMP is the Internet Control Message Protocol. Most users will recognize the name through the use of tools such as ping and traceroute, as this is the protocol that these services run over among other things. Its primary purpose is to tell systems when they are trying to connect remotely if the other end is available. Like TCP and UDP, it is a part of the IP suite and uses IP port number @Please note, this is not TCP port 1 or UDP port 1 as this is a different numbering scheme that for reference can be located here (For your reference, TCP uses IP port 6, while UDP uses IP port 17). That being said, different functions of ICMP use specific ports on TCP and UDP. For example, the 'echo' portion of ping (the part where someone else is able to ping you) uses TCP port 7.

Virtual Machines have only recently come into mainstream use, however they have been around under many different names for a long time. With the massive growth of hardware outstripping software requirements, it is now possible to have a server lying dormant 90% of the time while having other older systems at max capacity. Virtualizing those systems would allow the older operating systems to be copied completely and running alongside the server operating system- allowing the use of the newer more reliable hardware without losing any information on the legacy systems. On top of this, it allows for much easier backup solutions as everything is on a single server.

Giving a user as few privileges as possible tends to cause some aggravation by the user, but by the same token it also removes a lot of easily preventable infection vectors. Still, sometimes users need to have local admin rights in order to troubleshoot issues- especially if they're on the road with a laptop. Therefore, creating a local admin account may sometimes be the most effective way to keep these privileges separate.

To make a baseband network practical for many computers to share, the data transmitted by each system is broken up into separate units called packets. When your computer transmits data it might be broken up into many packets, and the computer transmits each packet separately. When all of the packets constituting a particular transmission reach their destination, the receiving computer reassembles them back into original data. This is the basis for a packet-switching network.

Circuit-switching means that the two systems wanting to communicate establish a circuit before they transmit any information. That circuit remains open throughout the life of the exchange, and is only broken when the two systems are finished communicating. Circuit switching is more common in environments like the public switched telephone network (PSTN), in which the connection between your telephone and that of the person you're calling remains open for the entire duration of the call.

The process of routing is done by the devices known as Routers. Routers are the network layer devices.

Sticky ports are one of the network admin's best friends and worst headaches. They allow you to set up your network so that each port on a switch only permits one (or a number that you specify) computer to connect on that port by locking it to a particular MAC address. If any other computer plugs into that port, the port shuts down and you receive a call that they can't connect anymore. If you were the one that originally ran all the network connections then this isn't a big issue, and likewise if it is a predictable pattern then it also isn't an issue. However if you're working in a hand-me-down network where chaos is the norm then you might end up spending a while toning out exactly what they are connecting to.

RIP depends on number of hops to determine the best route to the network while, IGRP considers many factors before decides the best route to take i.e. bandwidth, reliability, MTU and hops count.

RDP or Remote Desktop Protocol is the primary method by which Windows Systems can be remotely accessed for troubleshooting and is a software-driven method. KVM or Keyboard Video and Mouse on the other hand allows for the fast-switching between many different systems, but using the same keyboard, monitor and mouse for all. KVM is usually a hardware-driven system, with a junction box placed between the user and the systems in question- but there are some options that are enhanced by software. KVM also doesn't require an active network connection, so it can be very useful for using the same setup on multiple networks without having cross-talk.

At first glance it may be difficult to judge the difference between a hub and a switch since both look roughly the same. They both have a large number of potential connections and are used for the same basic purpose- to create a network. However the biggest difference is not on the outside, but on the inside in the way that they handle connections. In the case of a hub, it broadcasts all data to every port. This can make for serious security and reliability concerns, as well as cause a number of collisions to occur on the network. Old style hubs and present-day wireless access points use this technique.

Switches on the other hand create connections dynamically, so that usually only the requesting port can receive the information destined for it. An exception to this rule is that if the switch has its maintenance port turned on for an NIDS implementation, it may copy all data going across the switch to a particular port in order to scan it for problems. The easiest way to make sense of it all is by thinking about it in the case of old style phone connections. A hub would be a 'party line' where everybody is talking all at the same time. It is possible to transmit on such a system, but it can be very hectic and potentially release information to people that you don't want to have access to it. A switch on the other hand is like a phone operator- creating connections between ports on an as-needed basis.

Services are programs that run in the background based on a particular system status such as startup. Services exist across nearly all modern operating systems, although vary in their naming conventions depending on the OS- for example, services are referred to as daemons in Unix/Linux-type operating systems. Services also have the ability to set up actions to be done if the program stops or is closed down. In this way, they can be configured to remain running at all times.

FTP or File Transfer Protocol, is one of the big legacy protocols that probably should be retired. FTP is primarily designed for large file transfers, with the capability of resuming downloads if they are interrupted. Access to an FTP server can be accomplished using two different techniques: Anonymous access and Standard Login. Both of these are basically the same, except Anonymous access does not require an active user login while a Standard Login does. Here's where the big problem with FTP lies however- the credentials of the user are transmitted in cleartext which means that anybody listening on the wire could sniff the credentials extremely easily. Two competing implementations of FTP that take care this issue are SFTP (FTP over SSH) and FTPS (FTP with SSL). FTP uses TCP ports 20 and 21.

Routing protocol specifies how the routers communicate, disseminating the information which enables the routers to be selected between two nodes in a network.

A set of standards that define all operations within a network. There are various protocols that operate at various levels of the OSI network model such as transport protocols include TCP.

Routing protocol interacts and informs the hardware that is needed to transmit the data between transmitter and the receiver for transmission over network.

SSH or Secure Shell is most well known by Linux users, but has a great deal that it can be used for. SSH is designed to create a secure tunnel between devices, whether that be systems, switches, thermostats, toasters, etc. SSH also has a unique ability to tunnel other programs through it, similar in concept to a VPN so even insecure programs or programs running across unsecure connections can be used in a secure state if configured correctly. SSH runs over TCP port 22.

The International Organization for Standardization (ISO) developed the Open Systems Interconnection (OSI) Reference Model to describe how information is transferred from one machine to another.

When trying to communicate with systems on the inside of a secured network, it can be very difficult to do so from the outside- and with good reason. Therefore, the use of a port forwarding table within the router itself or other connection management device, can allow for specific traffic to be automatically forwarded on to a particular destination. For example, if you had a web server running on your network and you wanted access to be granted to it from the outside, you would setup port forwarding to port 80 on the server in question. This would mean that anyone putting in your IP address in a web browser would be connected up to the server's website immediately. Please note, this is usually not recommended to allow access to a server from the outside directly into your network.

Voice over Internet Protocol (VoIP) is the technology to send your voice (analog data) over the internet (digital data) to an end user. It enables users to use the Internet as the transmission medium for voice calls at a very low cost.

Although you may never have heard of this program, but if you have ever dealt with Apple devices you've seen its effects. Bonjour is one of the programs that come bundled with nearly every piece of Apple software (most notably iTunes) that handles a lot of its automatic discovery techniques. Best described as a hybrid of IPX and DNS, Bonjour discovers broadcasting objects on the network by using mDNS (multicast DNS) with little to no configuration required. Many admins will deliberately disable this service in a corporate environment due to potential security issues, however in a home environment it can be left up to the user to decide if the risk is worth the convenience.

Logon scripts are, surprisingly enough, scripts that run at logon time. These are used most times to allow for the continued access to share and device mapping as well as forcing updates and configuration changes. In this way, it allows for one-step modifications if servers get changed, shares get renamed, or printers get switched out for example.

The main goal of Distance Vector Routing Protocols Is to find out the best path for he data packet to reach the destination. Distance here could be the hops. The three different types of Distance Vector routing protocols include:- Routing Information Protocol (RIP v1 and v2) and Interior Gateway Routing Protocol. The protocol is easy to manage however not well scalable.

The Distance Vector protocol initially prepares a Routing table which is shared with other routers. This routing table is shared between routers present in the same network. A new routing table is prepared when some new information is received from some other router. Now, the bad routing paths are removed keeping only the smallest hop paths. This new table is then communicated to other routers.

A routing table stores the routes of the various nodes in a network. Nodes can be any electronic device connected to the network. The table is usually stored in a router or the network computer as a database or file. This information helps to fond the best possible path. The routing table has at least 3 fields: the destination network id, cost of the path, next hop or address to send the packet.

ROM:- Used to store the routers bootstrap details, operating system software.

Flash memory: - holds the operating systems images. The content is retained when the router is restarted.

RAM: - Used to store the Routing tables, configuration files, caching and buffering details. Content is lost when lost router is switched off or restarted.

NVRAM:- Stores the routers startup config files. Data is non volatile.

Network interfaces to connect router to network.

Switch

  • Switches are used at data link layer.
  • Switches create separate collision domain and a single broadcast domain.
  • Address learning
  • Forward/filter decision using mac address.

Hub

  • Hubs are used at physical layer.
  • Hubs create single collision domain and a single broadcast domain.
  • No addressing.
  • No filtering.

Shadow copies are a versioning system in place on Windows operating systems. This allows for users to go back to a previously available version of a file without the need for restoring the file from a standard backup- although the specific features of shadow copies vary from version to version of the OS. While it is not necessary to use a backup function in conjunction with Shadow Copies, it is recommended due to the additional stability and reliability it provides. Please note- Shadow Copies are not Delta Files. Delta files allow for easy comparison between versions of files, while Shadow Copies store entire previous versions of the files.

A cooperative trade association responsible for the "Commercial Building Telecommunication Cabling Standard," also known as EIA/TIA 568, which specifies how network cables should be installed in a commercial site.

Dynamic Host Configuration Protocol is the default way for connecting up to a network. The implementation varies across Operating Systems, but the simple explanation is that there is a server on the network that hands out IP addresses when requested. Upon connecting to a network, a DHCP request will be sent out from a new member system. The DHCP server will respond and issue an address lease for a varying amount of time. If the system connects to another network, it will be issued a new address by that server but if it re-connects to the original network before the lease is up- it will be re-issued that same address that it had before.

To illustrate this point, say you have your phone set to wifi at your home. It will pick up a DHCP address from your router, before you head to work and connect to your corporate network. It will be issued a new address by your DHCP server before you go to starbucks for your mid-morning coffee where you'll get another address there, then at the local restaurant where you get lunch, then at the grocery store, and so on and so on.

Virtual terminals: For accessing routers 

Network management stations.

/etc/passwd is the primary file in Unix/Linux operating system that stores information about user accounts and can be read by all users. /etc/shadow many times is used by the operating system instead due to security concerns and increased hashing capabilities. /etc/shadow more often than not is highly restricted to privileged users.

Boot to LAN is most often used when you are doing a fresh install on a system. What you would do is setup a network-based installer capable of network-booting via PXE. Boot to LAN enables this by allowing a pre-boot environment to look for a DHCP server and connect to the broadcasting network installation server. Environments that have very large numbers of systems more often than not have the capability of pushing out images via the network. This reduces the amount of hands-on time that is required on each system, and keeps the installs more consistent.

Being able to ping out to a server and see if its responding is a great way to troubleshoot connectivity issues. But what if you're not able to ping ANY server? Does that mean that your entire network is down? Does it mean that your network cable needs to be replaced? Does it mean that your network card is going bad? Or could it possibly be that sunspots, magnets, aliens and the Men In Black are all conspiring against you? The answers to these questions could be very difficult, but at the very least you can rule out if your network card is going bad. 127.0.0.1 is the loopback connection on your network interface card (NIC)- pinging this address will see if it is responding. If the ping is successful, then the hardware is good. If it isn't, then you might have some maintenance in your future. 127.0.0.1 and localhost mean the same thing as far as most functions are concerned, however be careful when using them in situations like web programming as browsers can treat them very differently.

  • RJ-11 ( Registered Jack-11) a four- or six-wire connector primarily used to connect telephone equipment.
  • RJ-45 (Registered Jack-45) connector is an eight-wire connector that is commonly used to connect computers to a local area network (LAN), particularly Ethernet LANs.
  • AUI( Attachment Unit Interface.) is the part of the Ethernet standard that specifies how a Thicknet cable is to be connected to an Ethernet card. AUI specifies a coaxial cable connected to a transceiver that plugs into a 15-pin socket on the network interface card (NIC).
  • BNC stand for British Naval Connector (or Bayonet Nut Connector or Bayonet Neill Concelman)a type of connector used with coaxial cables such as RG-58.BNC connectors are used on both Thicknet and Thinnet.

VoIP is far better than traditional telephony but it has some drawbacks as listed below:

  • Some VoIP services don't work during power outages and the service provider may not offer backup power.
  • Not all VoIP services connect directly to emergency services through 9-1-@
  • VoIP providers may or may not offer directory assistance/white page listings.

Transport layer assigns a unique set of numbers for each connection. These numbers are called port or socket numbers TCP, and UDP, provide a multiplexing function for a device: This allows multiple applications to simultaneously send and receive data.

The main purpose of data link layer is to check that whether messages are sent to the right devices. Another function of data link layer is framing.

Similar to how a DNS server caches the addresses of accessed websites, a proxy server caches the contents of those websites and handles the heavy lifting of access and retrieval for users. Proxy servers can also maintain a list of blacklisted and whitelisted websites so as to prevent users from getting easily preventable infections. Depending on the intentions of the company, Proxy servers can also be used for monitoring web activity by users to make sure that sensitive information is not leaving the building. Proxy servers also exist as Web Proxy servers, allowing users to either not reveal their true access point to websites they are accessing and/or getting around region blocking.

HTTP or HyperText Transfer Protocol, is the main protocol responsible for shiny content on the Web. Most webpages still use this protocol to transmit their basic website content and allows for the display and navigation of 'hypertext' or links. While HTTP can use a number of different carrier protocols to go from system to system, the primary protocol and port used is TCP port 80.

UTP cable comes in a variety of different grades, called "categories" by the Electronics Industry Association (EIA) and the Telecommunications Industry Association (TIA), the combination being referred to as EIA/TIA.

  • Cat 1 :- Used for voice-grade telephone networks only; not for data transmissions
  • Cat 2 :- Used for voice-grade telephone networks
  • Cat 3 :-Used for voice-grade telephone networks, 10 Mbps Ethernet, 4 Mbps Token Ring,
  • Cat 4 :-Used for 16 Mbps Token Ring networks
  • Cat 5 :-Used for 100BaseTX Fast Ethernet, SONet, and OC-3 ATM
  • Cat 5e:- Used for Gigabit (1000 Mbps) Ethernet protocols

  • Use a minimum password length of 12 to 14 characters if permitted.
  • Include lowercase and uppercase alphabetic characters, numbers and symbols if permitted.
  • Generate passwords randomly where feasible.
  • Avoid using the same password twice (eg. across multiple user accounts and/or software systems).
  • Avoid character repetition, keyboard patterns, dictionary words, letter or number sequences, usernames, relative or pet names, romantic links (current or past) and biographical information (e.g. ID numbers, ancestors' names or dates).
  • Avoid using information that is or might become publicly associated with the user or the account.
  • Avoid using information that the user's colleagues and/or acquaintances might know to be associated with the user.
  • Do not use passwords which consist wholly of any simple combination of the aforementioned weak components.

A straight-through cable is used for DTE-to-DCE connections.

  • A hub to a router, PC, or file server
  • A switch to a router, PC, or file server

Crossover cables should by used when you connect a DTE to another DTE or a DCE to another DCE.

  • A hub to another hub
  • A switch to another switch
  • A hub to a switch
  • A PC, router, or file server to another PC, router, or file server

A type of signal interference caused by signals transmitted on one pair of wires bleeding over into the other pairs. Crosstalk can cause network signals to degrade, eventually rendering them unviable.