Cisco Certified Network Professional (CCNP) – Enterprise interview questions

An MTU mismatch on the link: the routers cannot exchange database descriptor packets. Compare interface MTU on both sides with show interface, fix it (or, as a last resort, use ip ospf mtu-ignore). Duplicate router IDs can also cause odd adjacency problems.

What they are checking: Knowing OSPF states map to specific faults.

Likely follow-up: What causes neighbours to stay in INIT or 2-WAY?

In order: highest weight (Cisco), highest local preference, locally originated, shortest AS path, lowest origin type, lowest MED, eBGP over iBGP, lowest IGP metric to the next hop, then tie-breakers such as oldest route and lowest router ID. In practice you steer outbound traffic with local preference and inbound with AS-path prepending or MED.

What they are checking: Knowing the order and which attributes you actually use.

Likely follow-up: How would you make one ISP the backup link for inbound traffic?

If you leave defaults, any switch can become root, often an old access switch, giving bad traffic paths. Set the root and backup root on the core or distribution switches, use Rapid PVST+ or MST for fast convergence, and protect edges with PortFast, BPDU Guard and Root Guard. Without them a user plugging in a switch can cause a loop or a root change.

What they are checking: A deliberate STP design with protection features.

Likely follow-up: What does BPDU Guard do when it sees a BPDU?

All give a virtual default gateway. HSRP is Cisco-only, active/standby. VRRP is an open standard, very similar, and can use the real interface IP. GLBP is Cisco-only and load-balances across several gateways by answering ARP with different virtual MACs. Pair them with interface or object tracking so the gateway fails over when the uplink fails.

What they are checking: Differences plus tracking, which people often forget.

Likely follow-up: Why should HSRP active match the STP root for a VLAN?

It uses several cheaper transports (internet, LTE, MPLS) at once, with central policy, application-aware routing that moves traffic based on live loss and latency, and zero-touch provisioning for branches. It cuts cost and gives better visibility, though you must design security and underlay carefully.

What they are checking: Business and technical reasons together.

Likely follow-up: How does application-aware routing decide a path?

Coverage overlap and signal levels from a site survey, channel and power plans for co-channel interference, roaming features (802.11r fast transition, 802.11k/v), and the authentication method: full 802.1X on each roam adds delay unless fast roaming is enabled. Also check the client drivers.

What they are checking: RF plus authentication thinking.

Likely follow-up: What does 802.11r change during roaming?

To make changes consistently across many devices, back up configs, check compliance and pull data from APIs (RESTCONF, NETCONF, controllers) instead of logging into each box. It reduces human error and frees time for design work.

What they are checking: A practical view of automation.

Likely follow-up: What is the difference between NETCONF and RESTCONF?

802.1X with a RADIUS server such as Cisco ISE, so devices must authenticate before the port opens, with MAB as a fallback for printers and phones and a guest or quarantine VLAN for the rest. Simpler options are port security with sticky MACs and shutting unused ports.

What they are checking: A scalable answer, not only port security.

Likely follow-up: What is MAB and when is it used?

Work through the path: default route present and pointing the right way at the branch, NAT translations if internet breakout is local, ACLs added in the change, DNS resolution versus raw IP reachability, and the change itself compared with a config backup. traceroute shows where traffic stops.

What they are checking: Method plus comparing with the pre-change config.

Likely follow-up: How do you roll back a change on IOS XE quickly?

Keep it short: what users saw, how long, the cause in plain words, what we did to fix it and what we are doing so it does not happen again. Avoid jargon and blame. A written incident summary afterwards builds trust.

What they are checking: Clear communication under pressure.

Likely follow-up: What goes into a post-incident report?