What is the difference between layer 2 and layer 3 switches?
Theme: Routing and Switching Role: Network Engineer Function: Technology
Interview Question for Network Engineer: See sample answers, motivations & red flags for this common interview question. About Network Engineer: Designs and maintains computer networks. This role falls within the Technology function of a firm. See other interview questions & further information for this role here
Sample Answer
Example response for question delving into Routing and Switching with the key points that need to be covered in an effective response. Customize this to your own experience with concrete examples and evidence
- Functionality: Layer 2 switches operate at the data link layer (Layer 2) of the OSI model and are responsible for forwarding frames based on MAC addresses. Layer 3 switches, on the other hand, operate at the network layer (Layer 3) and can perform routing functions
- Addressing: Layer 2 switches use MAC addresses to forward frames within a local network. Layer 3 switches use both MAC addresses and IP addresses to make forwarding decisions, allowing them to route traffic between different networks
- Scalability: Layer 2 switches are typically used in local area networks (LANs) and are limited to forwarding frames within a single broadcast domain. Layer 3 switches, with their routing capabilities, can connect multiple LANs and route traffic between them, making them suitable for larger networks
- Broadcasts: Layer 2 switches forward broadcast frames to all ports within a broadcast domain. Layer 3 switches, however, can filter and control broadcast traffic, reducing unnecessary network congestion
- Security: Layer 2 switches do not provide any inherent security features. Layer 3 switches, on the other hand, can implement access control lists (ACLs) and other security measures at the network layer to control traffic flow and enhance network security
- Performance: Layer 2 switches operate at wire speed and have low latency since they only need to examine MAC addresses. Layer 3 switches, with their additional routing functionality, may introduce slightly higher latency due to the need for IP address lookups
- Cost: Layer 2 switches are generally less expensive than layer 3 switches since they have simpler functionality. Layer 3 switches, with their routing capabilities, tend to be more expensive but offer greater flexibility and scalability
- Use Cases: Layer 2 switches are commonly used in small to medium-sized LANs where simple network connectivity is required. Layer 3 switches are suitable for larger networks, such as enterprise networks, where routing between multiple LANs is necessary
- Interoperability: Layer 2 switches are compatible with any network device that operates at the data link layer. Layer 3 switches can seamlessly integrate with both layer 2 switches and routers, allowing for efficient network design and connectivity
Underlying Motivations
What the Interviewer is trying to find out about you and your experiences through this question
- Technical knowledge: Assessing the candidate's understanding of networking concepts and their ability to differentiate between layer 2 and layer 3 switches
- Experience: Determining if the candidate has hands-on experience working with layer 2 and layer 3 switches and can apply their knowledge in practical scenarios
- Problem-solving skills: Evaluating the candidate's ability to troubleshoot network issues by identifying the appropriate switch type based on the problem at hand
- Adaptability: Assessing if the candidate can adapt to different network environments and make informed decisions regarding the use of layer 2 or layer 3 switches based on the requirements
Potential Minefields
How to avoid some common minefields when answering this question in order to not raise any red flags
- Lack of knowledge: Not being able to explain the basic differences between layer 2 and layer 3 switches
- Confusion: Mixing up the functionalities and capabilities of layer 2 and layer 3 switches
- Inability to provide examples: Not being able to provide real-world examples of when to use layer 2 or layer 3 switches
- Overconfidence: Claiming to know everything about layer 2 and layer 3 switches without acknowledging any limitations or potential challenges
- Lack of troubleshooting skills: Not being able to explain how to troubleshoot common issues related to layer 2 and layer 3 switches
- Inability to discuss scalability: Not being able to discuss the scalability limitations of layer 2 switches compared to layer 3 switches
- Poor communication skills: Struggling to articulate the differences between layer 2 and layer 3 switches in a clear and concise manner