Curated interview practice questions with answers. These are practice scenarios, not a verified list of past interview questions.
About Ericsson hiring for CCNA roles
Ericsson is a Swedish telecommunications company that provides network equipment, software and services for mobile operators, including 4G and 5G radio, core networks and network management. In India it supports major telecom operators with network deployment and managed services, and runs research and development centres. It hires telecom engineers, software engineers, testers and network engineers.
For CCNA roles, this Ericsson practice set focuses most on Switching and VLANs (6), STP and EtherChannel (5), Wireless and Automation (5), IP Services (4). It has 11 easy, 17 medium, 2 hard questions, so you can start easy and work up to the harder ones.
Company type
Telecom
Headquarters
Stockholm, Sweden
Main India offices
Gurugram, Bengaluru, Chennai, Noida, Kolkata
Ericsson CCNA interview process
Online assessment (aptitude + technical)
Technical interview
Managerial round
HR round
Typical pattern based on public candidate experiences. Rounds vary by role, team and year.
Solved for EricssonStart practicing
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Quality of Service gives different treatment to traffic types when links are congested. Voice needs low delay (under 150 ms one way), low jitter (under 30 ms) and low loss (under 1 percent), while bulk file transfer can wait. QoS tools classify and mark traffic, queue it with priority queues for voice, and police or shape rates. Without congestion QoS has no effect.
02
A trunk between two switches is not forming. What would you check?
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.
03
How do you configure PortFast and BPDU Guard on access ports?
Apply per port or globally for all PortFast ports.
interface range GigabitEthernet1/0/1 - 46
switchport mode access
spanning-tree portfast
spanning-tree bpduguard enable
! or globally
spanning-tree portfast default
spanning-tree portfast bpduguard default
errdisable recovery cause bpduguard
errdisable recovery interval 300
04
What is the difference between a hub, a switch and a router?
A hub is a Layer 1 repeater: it floods every bit out of every port, so all ports share one collision domain. A switch is Layer 2: it learns MAC addresses and forwards frames only to the correct port, giving each port its own collision domain. A router is Layer 3: it forwards packets between IP networks and separates broadcast domains.
05
How do you restrict SSH access to devices from only the management subnet?
Use a standard ACL on the VTY lines.
ip access-list standard MGMT-ONLY
permit 10.99.0.0 0.0.0.255
deny any log
line vty 0 15
access-class MGMT-ONLY in
transport input ssh
exec-timeout 10 0
login block-for 120 attempts 3 within 60
06
An EtherChannel shows members in suspended state. What do you check?
Suspended (s) usually means a configuration mismatch between members or with the far end. I compare speed, duplex, trunk mode, native VLAN and allowed VLANs on each member and the port-channel with show run interface, check LACP modes on both sides, and look at logs. I fix the config on the port-channel, then shut and no shut members so they rejoin. show etherchannel summary should show P flags.
07
How do you handle pressure when an outage affects many users?
Situation: DHCP failed for 300 users at 9 a.m. on a Monday. Task: restore service while keeping managers updated. Action: I stayed calm, followed the bottom-up method, found the DHCP server's scope was full after a lease time change, extended the scope and shortened leases. I sent updates every 15 minutes. Result: users were back in 30 minutes, and we added scope utilisation alerts to monitoring.
Syslog has eight levels from 0 to 7: emergency, alert, critical, error, warning, notification, informational and debugging. A useful memory line is Every Awesome Computer Engineer Will Need Ice cream Daily. Setting logging trap 6 sends levels 0 to 6 to the server. Syslog uses UDP 514 by default, and logs should carry timestamps with service timestamps log datetime msec.
09
How does a router choose the best route to a destination?
First it uses longest prefix match: the most specific matching prefix wins, so 10.1.1.0/24 beats 10.1.0.0/16. If the same prefix comes from different sources, the lowest administrative distance wins. If the same protocol offers several paths, the lowest metric wins, and equal metrics can be load-balanced with ECMP. Only the winners are installed in the routing table.
802.1Q inserts a 4-byte tag after the source MAC in the Ethernet frame. The tag holds a 12-bit VLAN ID (1 to 4094 usable), 3 priority bits used by CoS for QoS, and a DEI bit. The tag is added when a frame leaves a trunk and removed at an access port. Older ISL encapsulation is obsolete; modern switches support only 802.1Q.
11
What is UDLD and why is it important on fiber links?
UniDirectional Link Detection sends probes to confirm a neighbour receives traffic in both directions. On fiber, one strand can fail so a port receives but cannot send, which may make STP unblock a port and create a loop. UDLD normal mode logs and marks the port, while aggressive mode err-disables it. It is commonly enabled on fiber uplinks together with Loop Guard.
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.
13
What are the basic steps to configure a WLAN with WPA2 or WPA3 on a controller GUI?
Steps on a typical WLC GUI: create a dynamic interface with VLAN, IP and DHCP server; go to WLANs and create a new WLAN with profile name and SSID; map it to the dynamic interface; under Security choose WPA2 or WPA3 with PSK or 802.1X and add the RADIUS server for enterprise; set QoS profile; enable the WLAN and apply it to AP groups.
14
What is the difference between site-to-site and remote-access VPNs?
A site-to-site VPN connects whole networks, usually two routers or firewalls, using an always-on IPsec tunnel, so users do not need any client. A remote-access VPN connects individual users from laptops or phones to the company network using a client with TLS or IPsec, and authenticates each user. Both encrypt traffic over the internet to provide confidentiality and integrity.
15
What is the difference between autonomous APs, controller-based APs and cloud-managed APs?
Autonomous APs are configured one by one and suit very small sites. Lightweight APs are managed by a Wireless LAN Controller using CAPWAP tunnels, which centralises configuration, RF management and roaming, and suits campuses. Cloud-managed APs are configured from a cloud dashboard, ideal for many branches. Split-MAC means real-time functions stay on the AP while management sits on the controller.
16
How does controller-based networking differ from traditional networking?
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.
A VLAN is a logical Layer 2 broadcast domain created on a switch, independent of physical location. VLANs separate users, voice, guests and servers, reduce broadcast traffic, and improve security because traffic between VLANs must pass through a router or Layer 3 switch where it can be filtered. For example, finance and guest Wi-Fi users can share switches but stay isolated.
18
What is inter-VLAN routing and what are the ways to do it?
Hosts in different VLANs need a Layer 3 device to communicate. Options are: a router with one physical interface per VLAN (legacy), router-on-a-stick using one trunk with subinterfaces, or a Layer 3 switch with switched virtual interfaces (SVIs). SVIs are the most common in campuses because routing happens in hardware at line rate, with no single trunk bottleneck.
19
Explain the NAT terms inside local, inside global, outside local and outside global.
Inside local is the private address of an inside host, for example 192.168.1.10. Inside global is the public address that represents it outside, for example 203.0.113.5. Outside global is the real address of the remote host. Outside local is how the remote host appears to inside users, usually the same as outside global unless destination NAT is used. show ip nat translations displays these columns.
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.
A floating static route is a backup static route with a higher administrative distance than the primary route, so it stays out of the routing table until the primary disappears. For example, if OSPF (AD 110) learns the main path, ip route 0.0.0.0 0.0.0.0 203.0.113.1 200 installs only when OSPF loses the route. It is common for backup internet or 4G links.
22
What is a collision domain and a broadcast domain?
A collision domain is a segment where two devices sending at the same time can collide; every switch port is its own collision domain, and with full duplex collisions do not occur. A broadcast domain is the set of devices that receive a Layer 2 broadcast. Routers and VLANs separate broadcast domains, so one VLAN equals one broadcast domain.
23
What are the default STP path costs for common link speeds?
With short (802.1D revised) costs: 10 Mbps is 100, 100 Mbps is 19, 1 Gbps is 4 and 10 Gbps is 2. With the long pathcost method, 1 Gbps is 20000 and 10 Gbps is 2000, which distinguishes higher speeds. Root path cost is the sum of costs on ports toward the root, and the lowest total wins when choosing root ports.
24
What is AAA and the difference between TACACS+ and RADIUS?
AAA stands for Authentication (who you are), Authorization (what you can do) and Accounting (what you did). TACACS+ uses TCP 49, encrypts the whole payload and separates authentication from authorization, so it is preferred for device administration with per-command control. RADIUS uses UDP 1812 and 1813, encrypts only the password and is used for network access such as 802.1X and VPN.
25
What is the native VLAN and what problems can a mismatch cause?
The native VLAN is the VLAN whose frames cross a trunk untagged, VLAN 1 by default. Both ends must use the same native VLAN; if they differ, frames leak between VLANs and CDP logs a native VLAN mismatch. For security, set the native VLAN to an unused ID, do not put users in it, and optionally tag it with vlan dot1q tag native to prevent VLAN hopping.
A voice VLAN lets an IP phone and a PC share one switch port while keeping their traffic separate. The port is an access port in the data VLAN, and the switch tells the phone through CDP or LLDP-MED to tag voice frames with the voice VLAN. This allows QoS priority for voice and separate addressing. Configure it with switchport voice vlan.
27
What is a wildcard mask and how is it used in ACLs?
A wildcard mask tells the router which bits must match: 0 means must match and 1 means ignore. It is often the inverse of the subnet mask, so 192.168.1.0 0.0.0.255 matches the whole /24. host 10.1.1.1 equals 0.0.0.0 and any equals 255.255.255.255. Wildcards are also used in OSPF network statements. Calculate it by subtracting the mask from 255.255.255.255.
28
How do you write a simple Python script to fetch interface data from a device?
Netmiko handles SSH sessions; keep credentials in a file or vault, not the script.
import yaml
from netmiko import ConnectHandler
# r1.yml holds device_type, host, username, password
with open('r1.yml') as f:
device = yaml.safe_load(f)
with ConnectHandler(**device) as conn:
output = conn.send_command('show ip interface brief')
print(output)
29
How do you call a REST API from Python and parse the JSON?
Use the requests library and convert the reply to a dictionary.
import requests
url = 'https://controller.example.local/api/v1/network-device'
headers = {'X-Auth-Token': token, 'Accept': 'application/json'}
r = requests.get(url, headers=headers, timeout=10)
r.raise_for_status()
for dev in r.json()['response']:
print(dev['hostname'], dev['managementIpAddress'])
30
How many usable hosts are in a /26 subnet and what is the block size?
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.
Tips to crack the Ericsson CCNA interview
Revise computer networks, TCP/IP, and basics of mobile communication such as LTE and 5G architecture before interviews.
Practise programming in C, C++, Java or Python, and be ready to solve simple coding and debugging problems.
Learn about Ericsson's role in 5G rollouts in India to discuss the industry and your interest in telecom.
Keep a one-minute story ready for every project on your CV: problem, your part, tools, result.
Practise the hard questions on this page aloud; Ericsson interviewers usually ask follow-ups on your first answer.
Frequently asked questions
How many rounds are there in the Ericsson CCNA interview?
Candidates usually go through 4 stages: Online assessment (aptitude + technical); Technical interview; Managerial round; HR round. The exact rounds change with the role, team, location and your experience, so confirm the process with the recruiter.
Which topics should I prepare for the Ericsson CCNA interview?
This practice set leans on Switching and VLANs (6), STP and EtherChannel (5), Wireless and Automation (5), IP Services (4). Revise those first, then practise explaining one or two of your own projects end to end, because most Ericsson interviewers ask you to walk through real work.
Are these the exact questions asked at Ericsson?
No. These are curated practice questions that match the skills and difficulty usually tested in telecom interviews like Ericsson's. They are not a leaked or verified list of past questions.
Where does Ericsson hire CCNA professionals in India?
Ericsson has large teams in Gurugram, Bengaluru, Chennai, Noida, Kolkata. Openings and locations change often, so check the Ericsson careers page and filter by city and experience.