A wireless network engineer plans, deploys and supports enterprise Wi-Fi. They run site surveys, plan 2.4 and 5 GHz channels, configure controllers and SSIDs with WPA2 or WPA3 Enterprise, integrate 802.1X with RADIUS, and troubleshoot roaming, coverage and AP join issues. Engineers with CCNA knowledge and one to four years of experience, plus hands-on controller work, are hired by IT services firms, campuses, hospitals and large offices.
Wireless controllers RF and channel planning WPA3 and 802.1X AP join troubleshooting Site surveys
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Allow web traffic from one subnet to a server and block the rest of that subnet.
ip access-list extended WEB-ONLY
10 permit tcp 192.168.10.0 0.0.0.255 host 10.0.0.80 eq 443
20 deny ip 192.168.10.0 0.0.0.255 10.0.0.0 0.0.0.255
30 permit ip any any
interface vlan 10
ip access-group WEB-ONLY in
show access-lists WEB-ONLY
02
What is port security and what are its violation modes?
Port security limits the MAC addresses allowed on an access port, either statically or by sticky learning. If an extra MAC appears, the violation mode acts: shutdown (default) err-disables the port, restrict drops the frames, logs and increments a counter, and protect silently drops frames. It stops MAC flooding and unauthorised devices on user ports.
03
After adding a new VLAN, users on one access switch cannot use it but others can. Why?
The most likely cause is the trunk to that switch does not allow the new VLAN, because someone configured an explicit allowed list. Check show interfaces trunk and add it with switchport trunk allowed vlan add 50, not without add, which would replace the list. Also confirm the VLAN exists on that switch with show vlan brief, especially if VTP is transparent.
Physical ports include service ports for out-of-band management, distribution system ports that connect to the switch as trunks, and redundancy ports for HA. Logical interfaces include the management interface used for CAPWAP and admin access, dynamic interfaces that map WLANs to VLANs, and a virtual interface used for web auth and DHCP relay. A LAG bundles distribution ports.
Control and Provisioning of Wireless Access Points is the protocol between lightweight APs and the WLC. It builds two tunnels: a control tunnel on UDP 5246, encrypted with DTLS, and a data tunnel on UDP 5247 that carries client traffic in central switching mode. In FlexConnect or local switching mode, client data is switched locally at the AP instead of being tunnelled.
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.
07
What are DR and BDR in OSPF and why are they needed?
On multi-access networks such as Ethernet, a full mesh of adjacencies would create too many LSAs. OSPF elects a Designated Router and Backup DR; other routers (DROTHERs) form full adjacency only with them and stay 2-Way with each other. The highest interface priority wins, then highest router ID; priority 0 means never DR. Election is non-preemptive, so a new better router does not take over.
08
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.
09
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.
10
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.
11
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.
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.
13
How do you check interface status and errors on an IOS device?
show ip interface brief gives status and IP of all interfaces, and show interfaces gives counters and duplex.
Router# show ip interface brief
Router# show interfaces GigabitEthernet0/1
Router# show interfaces status
Router# clear counters GigabitEthernet0/1
Status up/down means Layer 1 is up but Layer 2 keepalives fail; administratively down means the interface is shut.
A Layer 3 switch forwards packets between VLANs in hardware using SVIs or routed ports, giving very high throughput with many Ethernet ports. A router usually has fewer ports but richer WAN features such as NAT, VPN, deep QoS, varied WAN interfaces and large routing tables. In campuses, Layer 3 switches handle inter-VLAN routing while routers or firewalls handle the edge.
Redundant Layer 2 links create loops, and Ethernet frames have no TTL, so broadcasts circulate forever, causing broadcast storms, MAC table instability and duplicate frames. STP (802.1D) blocks redundant paths so there is one loop-free path to every switch, and unblocks a backup link if the active one fails. Without it, a single loop can take down a whole campus within seconds.
17
A security scan shows that switch and router management interfaces are reachable from user VLANs. How do you lock down management access?
Move management to a dedicated VLAN or out-of-band network, ideally in a management VRF. Apply an access-class ACL on VTY lines allowing only the jump host subnet, disable Telnet and HTTP, keep SSH version 2 and HTTPS only if needed, and use AAA with TACACS+ for per-user login and logging. Add control plane policing, block management subnets at the user VLAN gateways and rescan to confirm the fix.
18
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.
19
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.
20
Guest Wi-Fi users must reach only the internet, not internal networks. How do you enforce it?
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.
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.
22
How do you configure inter-VLAN routing on a Layer 3 switch with SVIs?
Enable routing and create an SVI per VLAN as the gateway.
ip routing
interface vlan 10
ip address 192.168.10.1 255.255.255.0
ip helper-address 10.0.0.50
no shutdown
interface vlan 20
ip address 192.168.20.1 255.255.255.0
no shutdown
show ip route connected
23
Tell me about a time you automated or simplified a repetitive task.
Situation: our team manually backed up 80 router configs each week. Task: save time and avoid missed backups. Action: I enabled the archive feature with time-period on each device and later wrote a small Python script with Netmiko to pull and store configs in Git. Result: weekly effort dropped from four hours to zero, and we could see config differences after every change.
24
Tell me about a time you found a security issue and reported it.
Situation: during a routine audit I noticed SNMP v2c with the default community public on several access switches. Task: close the gap without disrupting monitoring. Action: I reported it to my lead with evidence, proposed SNMPv3 with an ACL, tested with the monitoring team and rolled out in two batches. Result: the risk was closed in a week and SNMP checks were added to our device baseline.
25
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
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.
Configure the same group and virtual IP on both switches, with higher priority on the active one.
interface vlan 10
ip address 192.168.10.2 255.255.255.0
standby version 2
standby 10 ip 192.168.10.1
standby 10 priority 110
standby 10 preempt
show standby brief
Hosts use 192.168.10.1 as their gateway.
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.
29
Write a simple Ansible playbook that configures NTP on IOS devices.
Situation: as a fresher I realised many interview questions asked about recent attacks. Task: build a habit of learning. Action: I follow vendor security advisories, CERT-In alerts and a few security newsletters, practise in a home lab with packet captures, and read the release notes of devices we use. Result: I can explain current threats in interviews and suggested patching a vulnerable IOS version in my internship.
31
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.
32
Tell me about a time you took initiative beyond your assigned work.
Situation: our team got many Wi-Fi complaints but had no data. Task: nobody had asked, but I wanted to find the cause. Action: I did a walk-through survey with a free tool, mapped channels and signal, and found three APs on the same 2.4 GHz channel and one dead AP. I shared a short report with fixes. Result: after the changes, Wi-Fi tickets dropped by about 60 percent in a month.
DAI checks ARP packets on untrusted ports against the DHCP snooping binding table and drops ARP replies whose IP-to-MAC mapping does not match. This stops ARP spoofing and man-in-the-middle attacks where an attacker claims to be the default gateway. Static hosts need ARP ACLs. It requires DHCP snooping enabled in the same VLAN and trusted uplink ports.
34
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.
VLAN Trunking Protocol shares VLAN definitions from a server switch to clients in the same VTP domain. Modes are server, client, transparent and off. The risk is that a switch with a higher configuration revision number can overwrite and wipe VLANs across the domain. Many networks use transparent mode or VTP version 3 with a primary server to avoid this.
36
A user's port keeps going into err-disabled state. How do you investigate?
I run show interfaces status err-disabled and show errdisable recovery to see the cause, such as psecure-violation, bpduguard or link-flap. If it is port security, the user may have plugged in a small switch or a docking station with an extra MAC, so I check show port-security interface. I fix the cause, then shut and no shut the port, or set the max MAC count appropriately.
WPA2 uses AES-CCMP; WPA2-Personal uses a pre-shared key that is vulnerable to offline dictionary attacks, and WPA2-Enterprise uses 802.1X with RADIUS. WPA3-Personal replaces PSK with SAE, which resists offline guessing and gives forward secrecy. WPA3-Enterprise offers a 192-bit mode. WPA3 requires protected management frames. Open networks can use OWE for encryption without passwords.
38
How would you represent an interface configuration in JSON and YAML?
The same data in both formats.
JSON:
{
"interface": "GigabitEthernet0/1",
"enabled": true,
"ipv4": ["192.168.1.1/24"]
}
YAML:
interface: GigabitEthernet0/1
enabled: true
ipv4:
- 192.168.1.1/24
39
A new lightweight AP does not join the controller. How do you troubleshoot?
I check the AP gets a DHCP address and can reach the WLC management IP. It discovers the controller through DHCP option 43, the standard CAPWAP controller DNS name, broadcast or a primed controller IP, so I verify one of these. Then I check UDP 5246 and 5247 are not blocked, the AP's clock and certificate are valid, the country code matches, and the WLC has AP licences available.
40
What is the difference between an access port and a trunk port?
An access port belongs to one VLAN and carries untagged frames, typically to PCs, printers or servers. A trunk port carries traffic for many VLANs between switches, routers or hypervisors, adding an 802.1Q tag to identify each frame's VLAN, except the native VLAN which is sent untagged. Access ports can also carry a separate voice VLAN for IP phones.
Frequently asked questions
What does a Wireless Network Engineer do?
A wireless network engineer plans, deploys and supports enterprise Wi-Fi. They run site surveys, plan 2.4 and 5 GHz channels, configure controllers and SSIDs with WPA2 or WPA3 Enterprise, integrate 802.1X with RADIUS, and troubleshoot roaming, coverage and AP join issues. Engineers with CCNA knowledge and one to four years of experience, plus hands-on controller work, are hired by IT services firms, campuses, hospitals and large offices.
Which skills are tested in a Wireless Network Engineer interview?
Expect questions on Wireless controllers, RF and channel planning, WPA3 and 802.1X, AP join troubleshooting, Site surveys. Most rounds also ask you to explain a project and solve one practical problem live.
How do I prepare for a Wireless Network Engineer interview?
Revise Wireless and Automation, Network Security, Switching and VLANs first using the topic sheets, practise the questions on this page aloud, then do one full mock interview to practise timing.