Cisco Network Engineer Interview Questions: BGP, OSPF & 6 Answers

Last updated: October 2026

Quick Answer

Cisco network engineer interviews test protocol depth you can narrate: BGP session states and the best path order, OSPF adjacency problems and LSA types, spanning tree and VLANs, a troubleshooting scenario and usually a design question. Rehearse these aloud in the technical format of OphyAI Interview Practice.

Topic	What a strong answer shows
BGP	Six FSM states; Cisco’s best path order
OSPF	EXSTART versus 2-WAY; LSA types 1-5
Switching	Root bridge election, VLAN and trunk checks
Troubleshooting	An ordered packet-path diagnosis
Design	Trade-offs and which BGP knob does what

What Cisco Is Testing in This Round

Whether you have operated networks or only studied them; the Cisco interview guide calls protocol fluency the bar. Candidate reports describe scenario questions on spanning tree, BGP path selection and OSPF LSA types, then a managerial round.

Red flags that fail candidates:

• Reciting BGP attributes without saying which one they changed in production.
• Guessing a cause instead of working through ordered checks.
• Calling a 2-WAY OSPF neighbor “broken” on a broadcast segment, where it is normal.

What to Expect

• Format. Cisco says it interviews over Webex, by phone or in person, and that the process “varies by team and role”.
• Shape. One to three 45-60 minute technical rounds, then a techno-managerial round (candidate-reported); some loops start with the Cisco HackerRank online assessment.
• AI rules. Cisco’s How We Hire page says not to use AI to “create a script to read from to respond to an interview question” or to solve coding or design questions in real time; AI for preparation is welcome. See our tracker of companies that allow AI in interviews.

Example Questions and How to Answer Them

Built from reported topics; answers checked against RFCs and Cisco docs.

1. “A BGP peer is stuck in Active. What does that mean, and how is the best path chosen?”

Approach: RFC 4271 defines six states: Idle, Connect, Active, OpenSent, OpenConfirm, Established. Active means the router is still trying to complete the TCP connection on port 179. Check reachability to the peer, an ACL blocking TCP 179, the neighbor IP, and update-source or eBGP multihop for loopback peering. Then walk Cisco’s order: highest weight, highest local preference, locally originated, shortest AS path, lowest origin type, lowest MED, eBGP over iBGP, lowest IGP metric to the next hop, then the tie-breakers (oldest external path, lowest router ID). Name one you have tuned.

2. “Two OSPF neighbors are stuck in EXSTART. Another pair sits in 2-WAY. Which is the problem?”

Approach: EXSTART or EXCHANGE is the problem. Cisco says the usual cause is an MTU mismatch: RFC 2328 has a router reject Database Description packets whose Interface MTU is larger than it can accept. Match the MTU. 2-WAY between two DROTHERs on a broadcast segment is normal: routers go full only with the DR and BDR. If neighbors never appear, check what RFC 2328 requires to match in hellos: hello and dead intervals, mask, area and stub flag, plus authentication.

3. “Explain OSPF areas and the LSA types.”

Approach: Area 0 is the backbone; other areas attach through area border routers (ABRs). RFC 2328 defines five types: 1 router-LSA (every router, within its area), 2 network-LSA (the DR, for a transit segment), 3 summary-LSA for networks (ABRs, into other areas), 4 summary-LSA for the ASBR (ABRs), 5 AS-external (ASBRs, flooded everywhere except stub areas). Type 7 (NSSA) comes from RFC 3101.

4. “A new switch was plugged in and traffic now takes a strange path. What happened?”

Approach: It probably became root. The lowest bridge ID wins: priority (default 32768, plus the VLAN ID as extended system ID), then MAC address, so a lower MAC wins a tie. Set priority on the intended root and add root guard. Then cover port states (blocking, listening, learning, forwarding) and trunk checks: allowed VLANs, native VLAN mismatch.

5. “A user in a branch cannot reach a server in the data center. Walk me through it.”

Approach: Ask scope first: one user or all, since when. Then in order: the host’s IP, mask and gateway; ARP for the gateway; the routing table on each hop, where administrative distance picks between protocols (eBGP 20, OSPF 110, iBGP 200 on Cisco); ACLs and firewalls; the return path, since asymmetric routing breaks stateful firewalls; MTU if small pings work but transfers stall.

6. “Design a branch with two ISPs that survives one failing.”

Approach: Clarify failover time and whether you own an AS and addresses. Then: eBGP to both providers, local preference for the outbound exit, AS path prepending for inbound (MED is compared only between paths from the same neighboring AS by default), BFD for fast detection, and a first-hop redundancy protocol on the LAN.

How to Prepare in 1 Week

• Days 1-2: BGP. Write the states and the 13-step order from memory.
• Days 3-4: OSPF and switching. Draw adjacency states, LSA types and root election.
• Day 5: troubleshooting. Turn three scenarios (BGP down, OSPF stuck, one-way traffic) into ordered checklists.
• Day 6: mock. Run a technical mock in Interview Practice; its follow-ups push past your first answer.
• Day 7: stories. Prepare one outage story in STAR format.

Start practicing →

Common Mistakes

• Definitions without operations. Say which knob you used and what broke.
• Jumping to a cause. Ordered checks beat a lucky guess.
• Forgetting the return path. Many “unreachable” problems are one-way.

Related Guides

• Cisco interview guide (full loop and pay)
• Cisco HackerRank online assessment
• System design interview guide

Frequently Asked Questions

What questions are asked in a Cisco network engineer interview?

Candidate reports center on BGP best path selection, OSPF LSA types and adjacency problems, spanning tree and VLANs, and a troubleshooting scenario framed as a customer problem, with a design question in senior loops. Cisco publishes no question bank and says the process varies by team.

How many steps are in Cisco’s BGP best path algorithm?

Cisco’s “Select BGP Best-path Algorithm” document lists 13 steps, from highest weight down to lowest neighbor address. Weight is Cisco-specific and local to the router. Know the first eight cold, plus the main tie-breakers, and bring one real example of tuning local preference or AS path prepending.

Why is my OSPF neighbor stuck in EXSTART?

Usually an MTU mismatch. RFC 2328 has a router reject Database Description packets that advertise a larger MTU than it can accept, so the exchange never completes. Cisco’s troubleshooting note recommends matching the MTU on both interfaces. Stuck in 2-WAY on a broadcast segment between non-DR routers is normal.

Can I use AI during a Cisco interview?

No. Cisco’s How We Hire page says not to use AI to read a scripted interview answer or to generate a solution to a coding or design question in real time. It welcomes AI for preparation, such as tips and brainstorming approaches, so use it to practice beforehand.

Sources and verification notes

Checked October 2026; Glassdoor blocked fetches, so reported topics came from search summaries.

• Cisco, How We Hire: Webex, process varies, AI rules.
• Cisco, Select BGP Best-path Algorithm: the 13-step order.
• Cisco, Understand Administrative Distance: default distances.
• Cisco, OSPF neighbors stuck in Exstart/Exchange: MTU mismatch.
• Cisco, OSPF neighbors in two-way state: 2-WAY is normal.
• Cisco Catalyst 9300, Configuring Spanning Tree Protocol: root election, priority, port states.
• RFC 4271, BGP-4: states, TCP 179.
• RFC 2328, OSPF Version 2: hello checks (10.5), MTU check (10.6), LSA types.
• RFC 3101, OSPF NSSA: type-7 LSAs.
• Glassdoor, Cisco interviews: candidate-reported, via search summary.