Are you looking for job as a network design engineer? Or are you thinking to leave your current position for a new job as a network designer with a new company?

If you answered yes to either of those questions, then this article is for you and any of the described technologies and questions may be asked during the interview!

CCNP Training – Resources (Intense)

Network design engineer is a higher-level position; the major responsibility of a network design engineer is to design both the hardware and software technologies needed for a company’s network setup. A network designer examines vendor-agnostic network design principles and is often responsible for designing all of the network infrastructure, including routing, switching, security, LAN, WAN, VoIP, wireless, optimization, load balancing, etc. If you are more interested in network design and architecture, then don’t walk away from the equipment, open up your brain to new approaches building networks.

The scope of network designing is enormous (going through almost all networking specialization).

A network design engineer must have the knowledge of the following technologies:

  • Layer 2 control plane
  • Layer 3 control plane
  • VoIP, security, wireless network architecture
  • Network virtualization
  • Design considerations
  • Analyze design requirements
  • Develop and Implement network designs
  • Validate and optimize network design

I have read somewhere “there are those who design networks…. very large networks who may not do one ounce of actual installation or implementation of the network.”

Yes, it is possible that a person who has never worked on network technologies or seen even a router or switch can be a network designer. Equally, there are people who lay cables and configure routers and switches all day. In the middle ground are the amateur designers who will throw a solution together based on nothing but experience and reality, so it depends where you want to be as a network engineer.

The network designer in general focuses on the “Why“, where the network engineer (implementation) focuses on “How.” Designing track gives you concepts and processes that will enable you to better plan and lay out a network. It also gives you concepts such as the design lifecycle, network lifecycle, etc. It attempts to teach you different methodologies to sort through design problems and how to tackle them.

Also, the network designer has very broad technical knowledge where he/she needs strong logical and technological points of view because he/she needs to design with wireless, voice, and security in mind and not just routing and switching.

My Best Questions for an Interview of Network Design Engineer

All of the questions below are very common and must be prepared for before facing any interview for the network designing environment.

Q: What is your experience as a network design engineer?

A: You can answer with your wealth of network experience and job responsibilities and don’t forget to share your achievements as a network design engineer. You can also mention your involvement in complex LAN, WLAN, and IPT infrastructure solutions and large-scale projects in unique environments with collaboratively working within a team.

Basically, a network design engineer works with project teams, takes information and/or project specifications from customers and turns it into a completed design definition which meets the agreed specification, with due consideration to factors such as security and operational support including routing, switching, security, LAN, WAN, VoIP, wireless, optimization, load balancing, etc.

Q: What decisions/suggestions you have made as network design engineer?

A: Here you can provide the information on major suggestions/decisions taken by you on network/device migration and up-grading from your previous experience. You can also share your involvement in project review meetings and regular representation of the network services with your team, and how it helped your team to achieve organizational goals of network services.

Answer the question with all of positive decisions/suggestion taken by you and don’t try to explore decisions that were wrong in term of technical or any misfit technology but this doesn’t mean that you will not share your creativity and solution development skills.

Q: Describe the set of required skills for a network design engineer?

A: Answer this question with the description of required key skills for a network engineer as listed below;

• Layer 2 control plane
• Layer 3 control plane
• VoIP, security, wireless network architecture
• Network virtualization
• Design considerations
• Analyze design requirements
• Develop and implement network designs
• Validate and optimize network design

Q: Describe techniques you used as a network design engineer?

A: This question is asked very often during the interview for network designing position.

You must prepare the answer before facing the interview. You can start your answer with a list of technologies used by you. You might have to face cross-questioning for the described list of technologies.

You will be expected to share challenging timescales and demonstrate flexibility and sound design principles that allow your employer to meet the requirements of network project. You can also share your best-practice design methods that helped you to update and improve your way of working.

Q. How do traceroute and ping work?

A: Traceroute is a network debugging utility that attempts to trace the path a packet takes through the network. when you execute a traceroute command, your machine sends out 3 UDP packets with a TTL (time-to-live) of 1.

Traceroute works by increasing the “time-to-live” value of each successive batch of packets sent. This keeps going until you reach the destination.

Ping: It sends an ICMP (Internet control message protocol) echo request to a specified interface on the network and, in response, it expects to receive an ICMP echo reply. By doing this, the program can test connectivity, gauge response time, etc.

Q: How many channels are in E1 and T1 link and what is the operational bandwidth of each channel in each link?

A: E1 link contains 32 channels while T1 link contains 24 digital channels and each channel of both T1/E1 gives you 64 kbps bandwidth.

An E1 link consists of 30B channels and 1D channel and each channel has 64k Bw.

So for E1 – you get 30*64 = 1920kbps

A T1 link consists of 23B channels and a D channel and each channel has 64k Bw. So for T1 – you get 23*64 = 1472kbps

Q. What are the main contents of a routing table?

A: A routing table contains the information necessary to forward a packet along the best path toward its destination.

A basic routing table includes the following information:

  • Destination network-id
  • Next hop
  • Exit Interface (outgoing network interface)
  • Administrative distance:
  • Metric: Assigns a cost to each available route so that the most cost-effective path can be chosen

Q: What is a route flap?

A: Route flapping occurs very often in computer networking when a router alternately advertises a destination network via one route then another in quick sequence; also if an interface on a router has a hardware failure, it will cause the router to announce it alternately as “up” and “down”.

Q: What basic set-up equipment is needed for VoIP?

A: For general VoIP set up we require the following things;

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

Q: Why do we use BGP?

A: Border gateway protocol is an exterior gateway protocol (EGP) used for routing between autonomous systems. TCP port 179 is used to establish session

We can use BGP in the following conditions:

  • Customer is connected to multiple Internet service providers (ISPs).
  • Service provider networks (Transit autonomous system).
  • In very large enterprise networks, where we can use BGP at core layer as a redundant routing protocol.

Q: Describe what a VPN is and how it works.

A: Virtual Private Network (VPN) creates a secure network connection over a public network such as the Internet. IPsec VPN means VPN over IP Security allows two or more users to communicate in a secure manner by authenticating and encrypting each IP packet of a communication session.

Q: What are delay, jitter and packet loss and how can we overcome these issues?

A: Network traffic often suffers from one or more of the following issues:

Delay: Excessive time required for a packet to traverse the network

Jitter: The uneven arrival of packets, considered as delay variation

Packet loss: Dropped packets are not retransmitted

QoS can be used to overcome these issues, especially for unified communication network traffic. A commonly used IntServ QoS tool is RSVP (resource reservation protocol), which provides QoS by guaranteeing treatment to a particular traffic flow.

And DiffServ QoS tool classifies different types of traffic and provides different levels

of service based on those distinctions.

Q: Describe high-level and low-level network design.

A: A HLD is referred to as software architecture; it provides an overview of solution, platform, system, product, or process. High-level design involves decomposing system into modules and representing the interfaces and invocation relationships among modules. A high-level design document will usually include a high-level architecture diagram depicting the components, interfaces, and networks that need to be further specified or developed.

LLD, also known as detailed design, is used to design internals of the individual modules identified during HLD. LLD describes each and every module in an elaborate manner so that the engineer can directly implement the network based on this.

The questions above are very tricky and important from the standpoint of clearing any interview for a network design engineer position. If you find any difficulty in answering any other questions, then you can write me @ Comment section and following links of my previous posts on Data/Security/Voice Interview preparation will make you more confident.

Tips for Preparing for an Interview

  • Study: Before an interview, take a quick recap of relevant technologies.
  • Updated Resume: Read your resume through; don’t copy and paste your resume. You must be aware of your strengths and weaknesses.
  • Professional Certifications: One of the best ways to prove the technical skills mentioned in your resume is through certifications. This gives a new employer an easy way to understand your knowledge level.
  • Updated LinkedIn Profile: Update your LinkedIn profile regularly; make sure that your work experience, qualifications, and project details match with your resume.

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