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CCNA Telephonic Interview Questions & Answers

30 questions for the telephonic interview stage — 18 easy, 12 medium.

About the telephonic interview round

The telephonic or screening round is a 15-30 minute call with a recruiter or engineer. It checks your basics, your CV and whether you can explain CCNA concepts clearly without a screen to point at.

Tips for the telephonic interview round

  • Keep your CV in front of you and be ready to explain every line on it.
  • Answer in short, clear sentences; there is no whiteboard, so structure matters.
  • Take the call somewhere quiet and confirm the time in advance.
  • Prepare one question to ask the interviewer at the end.
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01

What is the structure of an IPv6 address and how is it shortened?

IP Addressing and SubnettingEasy
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IPv6 addresses are 128 bits written as eight groups of four hex digits separated by colons. Leading zeros in each group can be dropped, and one run of consecutive all-zero groups can be replaced with :: only once. For example 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1. A typical LAN uses a /64 prefix.
02

What are SSID, BSSID and ESS?

Wireless and AutomationEasy
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The SSID is the network name users see. The BSSID is the MAC address of the access point radio serving a BSS, the basic service set of one AP and its clients. An ESS is multiple BSSs sharing the same SSID connected by a wired distribution system, so clients can roam between APs. Each AP can broadcast several SSIDs, each with its own BSSID.
03

Explain root port, designated port and blocked port.

STP and EtherChannelMedium
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Every non-root switch picks one root port, its best path to the root based on lowest root path cost, then lowest sender bridge ID, then lowest sender port ID. On each segment, the switch with the best path becomes the designated port and forwards. Every remaining port becomes non-designated and blocks. All ports on the root bridge are designated.
04

Compare distance vector and link state routing protocols.

Routing and OSPFMedium
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Distance vector protocols like RIP share their routing table with neighbours and trust what they hear, so they converge slowly and need loop prevention such as split horizon. Link state protocols like OSPF and IS-IS flood link state advertisements so each router builds a full topology map and runs Dijkstra's SPF algorithm. Link state converges faster and scales better but uses more memory and CPU.
05

How does controller-based networking differ from traditional networking?

Wireless and AutomationMedium
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Traditionally each device has its own control plane and is configured box by box. In controller-based or software-defined networking, a central controller holds the policy and pushes it to devices through southbound APIs such as NETCONF or OpenFlow, while applications talk to the controller through northbound REST APIs. This gives consistent configuration, automation and network-wide visibility.
06

What is a REST API and which HTTP methods map to CRUD?

Wireless and AutomationEasy
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A REST API exposes resources at URLs and is stateless, usually with JSON payloads over HTTPS. CRUD maps to HTTP verbs: POST creates, GET reads, PUT replaces or PATCH partly updates, and DELETE removes. Responses use status codes such as 200 OK, 201 Created, 401 Unauthorized, 404 Not Found and 500 Server Error. Controllers expose northbound REST APIs for automation.
07

Guest Wi-Fi users must reach only the internet, not internal networks. How do you enforce it?

Network SecurityMedium
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Put guests in their own VLAN and subnet, ideally terminating on a firewall or a separate VRF. Apply an inbound extended ACL on the guest SVI that permits DHCP and DNS to the allowed servers, denies all RFC 1918 destinations, and then permits any to the internet. Enable client isolation on the wireless side and rate limit the guest SSID so it cannot consume the WAN.
08

Where do you see yourself in five years in networking?

Wireless and AutomationEasy
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Situation: I started with CCNA and a support role. Task: build a clear path. Action: I plan to master routing, switching and wireless in the next two years, pass CCNP Enterprise, and build automation skills in Python and Ansible alongside cloud networking. Result I aim for: a network engineer or architect role leading campus and SD-WAN projects, mentoring juniors and owning designs end to end.
09

What is EtherChannel and its benefits?

STP and EtherChannelEasy
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EtherChannel bundles 2 to 8 physical links into one logical port-channel. STP sees it as one link, so all members forward instead of one being blocked. It adds bandwidth and redundancy, as one member failing does not drop the channel. Traffic is load-balanced per flow using a hash of MAC, IP or port fields, so a single flow still uses only one member link.
10

How are ACL entries processed and what is the implicit deny?

Network SecurityEasy
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ACL entries are checked top-down and the first match decides permit or deny; later lines are ignored. Every ACL ends with an invisible deny any, so traffic that matches no line is dropped. Therefore specific entries must come before general ones, and an ACL with only deny statements blocks everything. Always add a permit for allowed traffic and test after applying.
11

How do you verify VLANs, trunks and MAC learning on a switch?

Switching and VLANsEasy
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These show commands cover most VLAN troubleshooting. show vlan brief show interfaces trunk show interfaces Gi1/0/5 switchport show mac address-table vlan 20 show mac address-table address 0050.56ab.cdef show interfaces status They show VLAN membership, allowed and active VLANs on trunks, native VLAN and where each MAC was learned.
12

Describe a time you made a configuration mistake. How did you handle it?

IP Addressing and SubnettingMedium
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Situation: I applied a /25 mask instead of /24 on a core VLAN interface during a change window. Task: fix it fast and own the error. Action: monitoring alerted on half the users, I checked my change, corrected the mask within ten minutes and informed my lead immediately. Result: impact was short, and I added a peer-review step and a pre-written rollback to every change plan afterwards.
13

Users behind a router can reach local servers but not the internet after a firewall change. NAT is configured. What do you check?

IP ServicesMedium
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I check show ip nat translations to see whether translations appear when users browse. If none, I verify ip nat inside and ip nat outside on the correct interfaces, that the ACL used by NAT matches the user subnets, and that the overload interface has an IP. I also check the default route and run show ip nat statistics for hits and misses.
14

A trunk between two switches is not forming. What would you check?

Switching and VLANsMedium
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I check show interfaces trunk and show interfaces switchport on both sides. Common causes are mismatched modes (both dynamic auto), one side hard-coded as access, encapsulation not set on older switches, or the port being err-disabled. Native VLAN mismatch and allowed list differences do not stop the trunk but break traffic. Best fix is switchport mode trunk on both ends with nonegotiate.
15

How does DHCP snooping protect the network?

Network SecurityMedium
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DHCP snooping classifies ports as trusted (uplinks toward real DHCP servers) or untrusted (user ports). Server messages such as Offer and Ack arriving on untrusted ports are dropped, which stops rogue DHCP servers. It also builds a binding table of MAC, IP, VLAN and port, which Dynamic ARP Inspection and IP Source Guard use. Rate limits on untrusted ports prevent DHCP starvation.
16

Why do you want to build a career in networking?

Network FundamentalsEasy
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Situation: in college I set up the hostel Wi-Fi and LAN for 120 students. Task: fix constant drop-outs. Action: I learned VLANs, channel planning and DHCP, then practiced every CCNA topic in Packet Tracer and GNS3. Result: complaints dropped sharply, and I realised I enjoy solving real problems that affect many people. Networking underpins cloud, security and automation, so it gives me a long and growing career path.
17

How does OSPF form a neighbour adjacency?

Routing and OSPFMedium
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Routers send hellos to 224.0.0.5. They become neighbours if area ID, subnet and mask, hello and dead timers, authentication and stub flags match, and the router IDs are unique. States go Down, Init, 2-Way, ExStart, Exchange, Loading and Full. In ExStart and Exchange they agree master and slave and swap database descriptions, which is where an MTU mismatch causes a stuck adjacency.
18

What is the difference between running-config and startup-config?

Network FundamentalsEasy
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running-config lives in RAM and holds the active configuration, so every change applies immediately but is lost on reload. startup-config is stored in NVRAM and is loaded at boot. You save with copy running-config startup-config or write memory. To roll back unsaved changes you can reload without saving, which is why many engineers use reload in 10 before risky remote changes.
19

What are the seven layers of the OSI model?

Network FundamentalsEasy
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From bottom to top: Physical, Data Link, Network, Transport, Session, Presentation and Application. Each layer serves the one above it. For example, Ethernet frames work at Layer 2, IP packets at Layer 3 and TCP segments at Layer 4. Engineers use the model to troubleshoot bottom-up: check cables and link lights first, then MAC learning, then IP reachability.
20

How does ARP work and what is a gratuitous ARP?

IP Addressing and SubnettingEasy
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When a host needs the MAC for an IP on its subnet, it broadcasts an ARP request and the owner replies with a unicast ARP reply; the result is cached. For remote destinations the host ARPs for its default gateway. A gratuitous ARP is an unsolicited announcement of a host's own IP-to-MAC mapping, used after failover, for example by HSRP, to update switch and host tables.
21

Explain the TCP three-way handshake.

Network FundamentalsEasy
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The client sends a SYN with an initial sequence number. The server replies with SYN-ACK, acknowledging the client sequence and sending its own. The client sends an ACK and the session is established. Closing uses FIN and ACK from each side. A firewall that sees repeated SYNs without the final ACK may be looking at a SYN flood attack.
22

What is the difference between TCP and UDP?

Network FundamentalsEasy
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TCP is connection-oriented: it uses a three-way handshake, sequence numbers, acknowledgements, retransmission, windowing and flow control, so delivery is reliable and ordered. UDP is connectionless with an 8-byte header and no retransmission, so it is faster and lighter. HTTPS, SSH and SMTP use TCP; DNS queries, DHCP, SNMP, TFTP and voice or video RTP streams use UDP.
23

What is route summarization and how do you calculate a summary?

IP Addressing and SubnettingMedium
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Summarization advertises one prefix that covers several contiguous networks, shrinking routing tables and hiding instability. Write the networks in binary and keep the common leading bits. For 10.1.4.0/24 to 10.1.7.0/24, the third octet values 4 to 7 share the first six bits (000001), so the summary is 10.1.4.0/22. Make sure the summary does not include networks that live elsewhere.
24

How is the OSPF router ID chosen?

Routing and OSPFEasy
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The router ID is a 32-bit value chosen in this order: manually configured router-id, then the highest IP on an up loopback interface, then the highest IP on an up physical interface. It is chosen when the OSPF process starts, so changes need clear ip ospf process. Best practice is to set it manually so it is stable and easy to recognise in the database.
25

What is SNMP and the differences between v2c and v3?

IP ServicesMedium
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SNMP lets a manager poll devices for counters and receive traps or informs about events, using a MIB with OIDs. Polling uses UDP 161 and traps UDP 162. SNMPv2c uses a plain-text community string with no encryption. SNMPv3 adds user-based authentication and encryption with authPriv mode, so it is the version to use in production, especially on networks reachable from many teams.
26

How does the TCP/IP model map to the OSI model?

Network FundamentalsEasy
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The TCP/IP model has four or five layers. Its Application layer covers OSI layers 5 to 7, Transport maps to Layer 4, Internet maps to Layer 3, and Network Access (or Link plus Physical) covers layers 1 and 2. CCNA uses the five-layer version. Real protocols such as HTTP, TCP and IP are defined by the TCP/IP suite, so it is the practical model.
27

What are the main 802.11 Wi-Fi standards?

Wireless and AutomationEasy
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802.11n (Wi-Fi 4) works on 2.4 and 5 GHz with MIMO. 802.11ac (Wi-Fi 5) is 5 GHz only with wider channels and MU-MIMO downlink. 802.11ax (Wi-Fi 6 and 6E) adds OFDMA, BSS colouring and target wake time, and 6E adds the 6 GHz band. 802.11be (Wi-Fi 7) adds 320 MHz channels and multi-link operation. India opened part of the 6 GHz band for indoor use.
28

How does DHCP work?

IP ServicesEasy
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DHCP uses the DORA process: the client broadcasts Discover, the server answers with an Offer, the client broadcasts a Request for that offer, and the server confirms with an Acknowledgement. The lease includes IP, mask, gateway, DNS servers and lease time. Clients renew at 50 percent of the lease. DHCP uses UDP ports 67 for the server and 68 for the client.
29

A PC in VLAN 20 cannot reach a PC in VLAN 30. What do you check?

Switching and VLANsMedium
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First I check each PC has the correct IP, mask and gateway for its VLAN. Then I confirm the switch ports are in the right VLANs with show vlan brief, and that the trunk to the Layer 3 device allows both VLANs using show interfaces trunk. On the Layer 3 device I check the SVIs or subinterfaces are up and have the right IPs, and that no ACL blocks the traffic.
30

How many usable hosts are in a /26 subnet and what is the block size?

IP Addressing and SubnettingEasy
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A /26 leaves 6 host bits, so 2 to the power 6 is 64 addresses and 62 usable hosts after removing network and broadcast. The mask is 255.255.255.192 and the block size is 256 minus 192, which is 64. So subnets of 192.168.1.0/26 start at .0, .64, .128 and .192. For 192.168.1.70/26 the network is .64 and broadcast .127.

Frequently asked questions

What happens in the CCNA telephonic interview round?

The telephonic or screening round is a 15-30 minute call with a recruiter or engineer. It checks your basics, your CV and whether you can explain CCNA concepts clearly without a screen to point at.

How do I clear the telephonic interview round?

Keep your CV in front of you and be ready to explain every line on it. Answer in short, clear sentences; there is no whiteboard, so structure matters. Take the call somewhere quiet and confirm the time in advance.

Which round comes next?

A typical order is online assessment, telephonic screening, one or two technical rounds, a managerial round and HR. Use the other round pages to practise each stage.

Practise every interview round

Online Assessment questionsTechnical Round questionsManagerial Round questionsRapid-Fire questionsHR & behavioural questionsFull mock interview

More ways to practise

Company-wise CCNA questionsExperience-wise CCNA questionsRole-wise CCNA questionsCity-wise CCNA questionsMost asked CCNA questionsScenario-based questionsPractical / hands-on questionsHR & behavioural questionsCCNA mock interviewOnline assessment questionsTechnical round questionsManagerial round questionsCCNA topic sheets