36 practice questions with answers for CCNA interviews in Delhi.
CCNA jobs in Delhi
Delhi NCR has one of India's biggest pools of IT, consulting, banking and start-up jobs. Delhi itself hosts many corporate, government-tech and consulting offices, and most candidates also apply across Noida and Gurgaon, so interviews here mix service-company and product-company styles.
Below are 36 questions that match the mix of service, product and domain employers hiring network support engineers in Delhi.
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01
Users suddenly receive IP addresses from a wrong subnet. What do you suspect and how do you fix it?
A rogue DHCP server, often a home router plugged into a wall port, is answering requests. I find it by checking the DHCP server IP on an affected client with ipconfig /all, then tracing its MAC with show mac address-table. I shut that port, and prevent it permanently by enabling DHCP snooping on user VLANs with only uplinks trusted.
02
How do you quickly calculate how many subnets and hosts a mask gives?
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.
04
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.
A private VLAN splits one VLAN into a primary VLAN and secondary VLANs. Isolated ports can talk only to promiscuous ports such as the gateway, while community ports can talk to each other and to promiscuous ports. It is used in hosting, DMZs and hotel networks to isolate customers on the same subnet without creating many subnets. It requires VTP transparent mode or VTP v3.
06
A server team says an ACL you applied blocked all traffic, including allowed services. What happened?
Most likely the ACL lacks a permit for normal traffic, so the implicit deny dropped everything, or the order put a broad deny above the specific permits. It may also be applied in the wrong direction or on the wrong interface. I check show access-lists for hit counts, fix the sequence by inserting lines, and add a final permit or the needed entries. I always test ACLs with a rollback timer.
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.
08
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.
09
Which QoS classes would you build for a typical branch WAN?
A simple five-class model works for most branches.
Voice (EF) priority queue, about 10 percent
Video (AF41) guaranteed 20-25 percent
Signalling (CS3) 5 percent
Business apps (AF21) 25-30 percent
Default (BE) remaining, with fair queuing
Scavenger (CS1) small share for backups and updates
10
How do you make an access switch port a routed port on a Layer 3 switch?
A routed port behaves like a router interface and does not belong to any VLAN.
interface GigabitEthernet1/0/1
no switchport
ip address 10.0.0.1 255.255.255.252
no shutdown
Routed uplinks between distribution and core avoid spanning tree on those links and allow fast routing convergence with ECMP.
11
How do you back up and restore a device configuration?
Copy the config to a server and back.
copy running-config tftp://10.0.0.40/R1-backup.cfg
copy running-config scp://admin@10.0.0.40/R1.cfg
copy tftp://10.0.0.40/R1-backup.cfg running-config
configure replace flash:R1-good.cfg
archive
path flash:R1-archive
write-memory
configure replace gives a clean rollback instead of merging.
12
Users complain Wi-Fi is slow in a conference room with 60 people. What do you check and fix?
This is usually a capacity, not a coverage, issue. I check client count per AP and channel utilisation on the controller. Fixes include adding APs with lower transmit power, steering clients to 5 or 6 GHz with band steering, disabling low data rates such as 1, 2 and 5.5 Mbps, using 20 or 40 MHz channels in dense areas, and limiting per-client bandwidth on the SSID.
Dynamic Trunking Protocol negotiates whether a link becomes a trunk. Modes are dynamic auto, dynamic desirable, trunk and access. Auto plus auto stays access, while desirable with auto or desirable forms a trunk. Attackers can use DTP to form a trunk and reach all VLANs, so best practice is to hard-code access or trunk and use switchport nonegotiate on trunks.
14
Describe a time you disagreed with a senior engineer about a network design. How did you handle it?
Situation: a senior engineer wanted static routes for twelve new branches. Task: I believed OSPF would scale better. Action: instead of arguing in the meeting, I built both options in a lab, measured failover time and listed the change effort for each. I shared the results privately first. Result: we agreed on OSPF with summarization at the hub, and he asked me to write the standard. I learned that data persuades better than opinions.
15
A PC can ping its default gateway but cannot open any website. How would you troubleshoot?
Gateway reachability proves Layers 1 to 3 locally, so I move upward. I ping a public IP address; if that works but names fail, DNS is the problem, so I check the configured DNS server with ipconfig /all and test with nslookup. If the public IP also fails, I check the router's default route, NAT and upstream link. Finally I check proxy settings and any firewall blocking ports 80 and 443.
16
A new VLAN's users do not get DHCP addresses, but other VLANs work. What do you check?
I check that the SVI for the new VLAN is up and has ip helper-address pointing to the DHCP server, that the server has a scope for that subnet with the right gateway, and that the scope is activated. I confirm the VLAN is allowed on trunks. If DHCP snooping is enabled, I check the uplink is trusted, otherwise offers from the server are dropped.
17
How do you configure a router as a DHCP relay and verify it?
Add the helper address on the client-facing interface.
interface vlan 20
ip helper-address 10.0.0.50
show ip interface vlan 20 | include Helper
debug ip dhcp server packet
The helper also forwards some other UDP broadcasts such as TFTP and DNS by default; use no ip forward-protocol udp to limit them.
Member interfaces must have the same speed and duplex, the same mode (access or trunk), the same access VLAN or the same native and allowed VLAN list on trunks, and compatible negotiation modes. Mismatched settings put members into suspended state. Configure settings on the port-channel interface so they are pushed to members, and verify with show etherchannel summary.
19
Describe a time you made a configuration mistake. How did you handle it?
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.
20
Your company is running out of IP addresses on a /24 user subnet. What options do you have?
Options: expand to a /23 if the adjacent block is free and update the router and DHCP scope; create a new VLAN and subnet for some users, which also limits broadcast size; shorten DHCP lease times if many guest devices hold leases; and move printers, phones and IoT devices to their own subnets. Long term, plan an addressing scheme with growth headroom and consider dual-stack IPv6.
21
How do you handle a change that must be done during a night window?
Situation: we had to migrate 30 access ports to new VLANs overnight. Task: finish with zero business impact. Action: I prepared configs in advance, got peer review, scheduled a rollback, informed the helpdesk and tested each floor with a laptop after changes. Result: the migration finished an hour early, morning tickets were zero, and the plan became our template for later VLAN changes.
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.
Set a router ID, enable OSPF on interfaces and make user ports passive.
router ospf 1
router-id 1.1.1.1
auto-cost reference-bandwidth 100000
passive-interface GigabitEthernet0/1
network 10.0.12.0 0.0.0.3 area 0
network 192.168.1.0 0.0.0.255 area 0
default-information originate
Or per interface: ip ospf 1 area 0
Global unicast (2000::/3) is publicly routable. Unique local (fc00::/7, in practice fd00::/8) is like private IPv4. Link-local (fe80::/10) is auto-created on every IPv6 interface and used for neighbour discovery and routing next hops. Multicast is ff00::/8, for example ff02::1 all nodes and ff02::2 all routers. Anycast is a unicast address shared by several devices. IPv6 has no broadcast.
25
An automation job pushed a wrong configuration to 50 switches and broke their uplinks. How do you recover and stop it happening again?
First stop the job, then recover through out-of-band console or a management network, using configuration archive rollback or a saved backup. In future, run changes with commit confirmed or reload in as a safety timer, test in a lab, use a dry run or check mode, deploy to one canary switch, then in small batches with automatic post-checks. Store templates in Git with peer review so every change is visible and reversible.
26
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.
Rapid PVST+ runs 802.1w per VLAN. It uses a proposal and agreement handshake on point-to-point links so ports move to forwarding in under a second, instead of waiting on timers. It has port roles root, designated, alternate and backup, and states discarding, learning and forwarding. Alternate ports provide an instant backup root port. It is the default on most modern IOS switches.
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
Traffic is taking a slow path because an old access switch became root bridge. How do you fix it?
The old switch has the lowest MAC with default priority, so it won the election. I set the core or distribution switch as root with spanning-tree vlan 1-4094 priority 4096, or root primary, and the secondary with 8192. I add Root Guard on distribution downlinks so access switches can never become root again. Then I verify with show spanning-tree root.
31
How do you use CDP and LLDP to discover neighbours?
CDP is a proprietary Layer 2 discovery protocol enabled by default on IOS; LLDP is the open IEEE 802.1AB standard.
show cdp neighbors
show cdp neighbors detail
configure terminal
lldp run
show lldp neighbors detail
Detail output shows the neighbour's IP, platform and port. Disable CDP on internet-facing ports with no cdp enable.
32
How do you verify VLANs, trunks and MAC learning on a switch?
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.
33
How are ACL entries processed and what is the implicit deny?
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.
Use one trunk link and a subinterface per VLAN with 802.1Q encapsulation.
interface GigabitEthernet0/0
no shutdown
interface GigabitEthernet0/0.10
encapsulation dot1Q 10
ip address 192.168.10.1 255.255.255.0
interface GigabitEthernet0/0.20
encapsulation dot1Q 20
ip address 192.168.20.1 255.255.255.0
The switch port facing the router must be a trunk.
Single-mode fiber has a small core (about 9 microns) and uses a laser, so it carries light over long distances, often 10 km or more. Multimode fiber has a larger core (50 or 62.5 microns), uses cheaper LED or VCSEL optics and suits shorter runs inside a building or data center, usually up to a few hundred metres at 10 Gbps. SFP modules must match the fiber type.
36
Compare Ansible, Puppet and Chef for network automation.
Ansible is agentless, uses SSH or APIs, writes playbooks in YAML and uses a push model, so it is the most popular for network devices. Puppet uses an agent, a declarative manifest language and a pull model. Chef uses Ruby-based recipes with an agent and pull model. Puppet and Chef are more common for servers. All support idempotent configuration management.
Frequently asked questions
Which companies hire CCNA professionals in Delhi?
Companies with large offices in Delhi include many IT services and product firms. Use their company pages below to practise employer-specific sets.
Are CCNA interviews in Delhi different from other cities?
The questions depend more on the company than the city. Delhi's mix of employers decides the style: Delhi itself hosts many corporate, government-tech and consulting offices, and most candidates also apply across Noida and Gurgaon, so interviews here mix service-company and product-company styles
How do I find CCNA jobs in Delhi?
Shortlist companies with Delhi offices, keep your CV focused on CCNA projects, apply on company career pages and job portals with the Delhi filter, and practise the questions on this page before each interview.