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ALOIS Software Engineer Interview Guide

ALOIS Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

As a Software Engineer at ALOIS, you are the architectural backbone of our global connectivity and security operations. While the title is Software Engineer, this specific requisition functions as a highly specialized Network Engineer. You will be responsible for the continuous operation, security, and optimization of our enterprise routing, switching, WAN, WLAN, and firewall systems. Your impact in this role is immediate and global. By leading gap analyses of international network sites and executing proactive maintenance, you ensure that our diverse, distributed teams can collaborate without friction. You will safeguard our infrastructure using advanced firewall and VPN technologies, directly contributing to the operational security and resilience of the entire firm.

This guide is scoped to a Software Engineer candidate at ALOIS.

Focus areas

  • Cisco Routers
  • Cisco Switches
  • Network Troubleshooting

The ALOIS interview process

ALOIS candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Recruiter Screen

Initial screening focused on your background, alignment with core values, and role requirements.

What to demonstrate

  • Initial screening focused on your background, alignment with core values, and role requirements
  • Depth in Cisco Routers

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Phone Screen

A rapid-fire assessment of foundational networking knowledge, specifically in Cisco environments.

What to demonstrate

  • A rapid-fire assessment of foundational networking knowledge, specifically in Cisco environments
  • Depth in Cisco Routers

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Virtual Onsite Loop

A series of deep-dive sessions testing routing, switching, wireless technologies, and firewall management.

What to demonstrate

  • A series of deep-dive sessions testing routing, switching, wireless technologies, and firewall management
  • Depth in Cisco Routers

How to prepare

  • Answer aloud and timed: What command-line tools do you rely on most when diagnosing a sudden drop in network performance on a Cisco switch?
  • Answer aloud and timed: How do you configure a site-to-site IPsec VPN, and what are the common reasons Phase 1 might fail?

Behavioral and Leadership Round

Discussion with the Network Engineering Manager focusing on project management skills and team integration.

What to demonstrate

  • Discussion with the Network Engineering Manager focusing on project management skills and team integration
  • Depth in Cisco Routers

How to prepare

  • Prepare three examples from your own work, each with a decision you made and an outcome you can quantify.
  • Re-read the description of the behavioral and leadership round above and write down what you would ask to confirm before it.

Where candidates lose points

Structure Your Troubleshooting

When given a break-fix scenario, do not jump straight to the solution. Explain your methodology. Start at Layer 1 (physical) and move up the OSI model. Interviewers care more about your logical process than a lucky guess.

Master Your Diagramming Explanations

Since Visio documentation is a core requirement, practice explaining network topologies visually. If you are in a virtual interview, be prepared to use a digital whiteboard to draw out your proposed BGP architecture or VPN topology.

Highlight Diversity and Teamwork

When answering behavioral questions, explicitly mention how you value different approaches to problem-solving. Show that you actively seek input from peers and respect diverse working styles, directly aligning with ALOIS’s mission statement.

Know the Hardware

Be specific about the platforms you have worked on. Mentioning specific Cisco Catalyst/Nexus models or Palo Alto series adds credibility to your 7–9 years of required experience.

Questions & practice

Walk me through how you would create a security policy on a Palo Alto firewall to block specific application t

Medium · Network Security & Firewalls

Walk me through how you would create a security policy on a Palo Alto firewall to block specific application traffic while allowing web browsing.

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Diff a projection against the primary without per-row point reads

Hard · reconciliation · range hashing · throttling

The listing projection has drifted and some rows show a stale version. The primary holds 40,000,000 resource rows across 12,000 tenants while serving 1,200 writes and 14,000 reads per second. The obvious repair, reading each resource row and comparing its version against the projection, is correct and would eventually finish. Explain precisely why it is unacceptable here, then give a diff that finds the differing rows, state its complexity, and make it safe to run against a live primary. Replication lag is usually under 100 ms and is not bounded.

Approach

  1. Quantify the naive cost rather than calling it slow: 40,000,000 point reads at even 0.5 ms each is over five hours serialised, and the only lever is concurrency, which is exactly what you cannot spend. The primary's pool is sized for the write path, and 40,000,000 random reads evict the buffer cache that sustains the 85 percent cache hit rate, so the audit degrades the system it is auditing.
  2. Replace random access with one ordered pass per side. Both sides can be read in (tenant_id, resource_id) order, which is a sequential scan on each and a merge join in O(n) time and O(1) memory. For a dense diff that is the whole answer, and it reads the primary once instead of 40,000,000 times.
  3. For the expected sparse case, compare range hashes instead of rows: partition the key space, compute per range an order-independent aggregate over hash(resource_id, version), compare aggregates, and descend only into ranges that differ. With d differing rows and branching factor B, at most d ranges mismatch per level, so the drill-down examines O(d log_B(n/d)) ranges and reads full rows only in mismatching leaves.
  4. Aggregate with a sum modulo 2^64 or a multiset hash, never XOR. XOR is order-independent but self-cancelling, so two rows wrong in the same way, or a row duplicated on one side, leave the range aggregate matching and the range is declared clean.

Follow-up

  • The diff reports 900 stale rows. How do you decide between patching those rows and rebuilding the projection from resource_revision?
  • Same job, but the projection lives in a search index that cannot be scanned in key order. What changes?

Canonicalise a request body into a stable idempotency fingerprint

Medium · parsing · canonicalisation · hashing

idempotency_key.request_fingerprint is a SHA-256 over the method, path and canonicalised body, and a retry whose fingerprint differs must be rejected with 422 rather than served the stored response. Write the canonicaliser. Bodies are JSON up to 256 KB nested at most 32 levels; clients vary key order, whitespace and unicode escaping, and some send 64-bit ids as JSON numbers. Produce a deterministic byte string such that semantically identical bodies match and any semantic difference does not. State your complexity and name two normalisations you refuse to perform.

Approach

  1. Parse once into a tree, then re-serialise under fixed rules: object keys sorted, array order preserved, one escaping convention, no insignificant whitespace. Parsing is O(n) and sorting keys is O(k log k) per object, so O(n log n) overall with O(depth) stack, and the 32-level cap is enforced during parsing because hostile nesting is how a canonicaliser becomes a stack overflow.
  2. Sort keys by their UTF-8 bytes and say why the obvious implementation is wrong in some runtimes: a default string comparison that orders by UTF-16 code units places surrogate pairs, meaning code points from U+10000 up, below U+E000 to U+FFFF, which is not UTF-8 byte order, so two services written in different languages disagree on the same document.
  3. Do not re-encode numbers through a double. IEEE-754 binary64 represents integers exactly only up to 2^53, so normalising a 19-digit id through a float changes it, and 1 against 1.0 cannot be reconciled without deciding whether they are the same value. Preserve the literal token, and require ids as strings at the API boundary if you want them comparable.
  4. Reject duplicate keys rather than picking one. JSON permits them and parsers disagree, most keeping the last, so any choice you make ties the fingerprint to a parser detail that the code handling the request does not necessarily share.

Follow-up

  • A client sends the same logical request with an extra field your API ignores. Same key, different fingerprint, so you return 422. Is that the right answer?
  • Where does the fingerprint get computed relative to request decompression and the body-size limit?

Denormalise tenant onto revisions and backfill it live

Hard · denormalisation · online migration · backfill

resource_revision (revision_id, resource_id, version, actor_user_id, change_kind, patch, request_id, created_at) has 400M rows and no tenant column; tenant_id lives only on resource. Two reads need it: a tenant-scoped audit feed ordered by created_at DESC, and an offboarding purge. Both join back to resource today. Justify adding tenant_id to resource_revision against those two reads, name the anomaly the copy introduces and the constraint that prevents it, then give the ordered migration for a live table taking 1.2k writes/second — the lock each step takes, how the backfill is batched, and where each step stops being reversible. PostgreSQL 16.

Approach

  1. Justify from the access path rather than from taste. Without the column, the audit feed either scans resource_revision by created_at and discards other tenants' rows, or resolves the tenant's resource_ids first and probes with them — both proportional to the tenant's whole history rather than to one page. With (tenant_id, created_at DESC, revision_id DESC) it is a seek that stops at 50 rows, and the purge becomes a ranged delete instead of a join.
  2. Name the cost exactly: a second copy of a fact can disagree with the first. Make the disagreement unwritable rather than documented — add UNIQUE (resource_id, tenant_id) on resource so it can serve as a foreign-key target, then FOREIGN KEY (resource_id, tenant_id) REFERENCES resource (resource_id, tenant_id) on the revision table. A revision can then only ever carry its parent's tenant.
  3. Step one, expand: ALTER TABLE resource_revision ADD COLUMN tenant_id BIGINT NULL, with no default, so it is a catalogue change and no rewrite. It still needs ACCESS EXCLUSIVE for an instant, and that instant queues behind the longest open transaction on the table while every later query queues behind it — set lock_timeout to 2s and retry rather than wait.
  4. Step two, dual-write: deploy the writer that populates tenant_id on every new revision while reads still use the join. Reversible by redeploying the previous build, because nothing reads the column yet.

Follow-up

  • The backfill is half finished and a rollback is required. What state is the table in, and what does the previous build do with a half-populated column?
  • How do you verify the backfill actually finished, given rows are still being inserted while it runs?

Explain why the owner filter ignores the listing index

Medium · composite index · query plans · sort elimination

The only index on resource is (tenant_id, status, updated_at DESC, resource_id DESC). A new endpoint returns one user's resources across all statuses, newest created first: WHERE tenant_id = $1 AND owner_user_id = $2 ORDER BY created_at DESC LIMIT 20. On a tenant with 2M rows it takes 900 ms and EXPLAIN shows a sort above a large scan. Explain precisely why the existing index cannot serve it, give the index that can, and state which of these the new index still will not help: owner_user_id alone across tenants; the same query ordered by updated_at. PostgreSQL 16.

Approach

  1. Separate the two jobs an index does. For filtering, a composite btree is seekable only on a left prefix, so with no predicate on status the scan can at best range over tenant_id and test owner_user_id per row; PostgreSQL 16 has no btree skip scan to jump the unconstrained column.
  2. For ordering, the index is sorted by (status, updated_at) within a tenant and not by created_at, so the LIMIT cannot stop early: every matching row is read and then sorted. That is the 'Sort Method: top-N heapsort' line, and it is why the plan reads 2M rows to answer with 20.
  3. Derive the replacement from the access path — equality, equality, then the ordering column: CREATE INDEX CONCURRENTLY ON resource (tenant_id, owner_user_id, created_at DESC). The scan seeks to the (tenant, owner) range and walks 20 entries in order, so the Sort node disappears along with the row-read.
  4. Treat INCLUDE (title, status) as conditional, not free. An index-only scan still visits the heap for any row whose page is not marked all-visible, so on a table taking 1.2k writes/second the win depends on autovacuum keeping the visibility map current, and the wider index costs more on every insert.

Follow-up

  • 90% of rows are status='active'. Would a partial index WHERE status = 'active' change your answer, and for which of the three queries?
  • A dashboard runs this for 40 owners in one page load. What changes about the design?

Explain the difference between BGP and OSPF, and describe a scenario where you would use each.

Medium · Core Routing & Switching

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How does Spanning Tree Protocol prevent network loops, and what are the differences between classic STP and RS

Medium · Core Routing & Switching

How does Spanning Tree Protocol prevent network loops, and what are the differences between classic STP and RSTP?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Walk me through the exact steps a router takes when it receives an IP packet destined for a different subnet.

Medium · Core Routing & Switching

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

What command-line tools do you rely on most when diagnosing a sudden drop in network performance on a Cisco sw

Medium · Core Routing & Switching

What command-line tools do you rely on most when diagnosing a sudden drop in network performance on a Cisco switch?

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How do you configure a site-to-site IPsec VPN, and what are the common reasons Phase 1 might fail?

Medium · Network Security & Firewalls

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain the concept of NAT. How is it implemented differently on a Cisco ASA versus a Palo Alto firewall?

Medium · Network Security & Firewalls

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

What is your approach to auditing legacy firewall rules to determine if they are still needed?

Medium · Network Security & Firewalls

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Describe a challenging VPN client-access issue you resolved for a remote executive.

Medium · Network Security & Firewalls

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain the role of a wireless LAN controller (WLC) in an enterprise environment.

Medium · Wireless & Enterprise Connectivity

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

What are the primary causes of co-channel interference, and how do you mitigate it in a high-density office?

Medium · Wireless & Enterprise Connectivity

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Describe the integration between an enterprise wireless network and a RADIUS server for 802.1X authentication.

Medium · Wireless & Enterprise Connectivity

Approach

  1. Say who the caller is and what they do when the call fails halfway.
  2. Define the identity of a request so a retry cannot double-apply it.
  3. Separate accepted, pending, failed and confirmed; they are different facts.
  4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

  • What happens if the caller retries after a timeout?
  • How does a client discover it is on an old version of this contract?

How do you troubleshoot a user who is experiencing intermittent disconnects from the corporate Aruba wireless

Medium · Wireless & Enterprise Connectivity

How do you troubleshoot a user who is experiencing intermittent disconnects from the corporate Aruba wireless network?

Approach

  1. Establish what changed and when, before forming any theory.
  2. Pick a bisection that eliminates candidates whichever way it turns out.
  3. Check the instrumentation before believing the symptom.
  4. Separate the trigger from the cause; the deploy is rarely the bug.

Follow-up

  • What would you look at first, and what would it rule out?
  • How would you tell a cause from a coincidence here?

Suggested practice checklist

Built from the rounds and topics ALOIS candidates report.

Day 1 — Map the ALOIS loop

  • Write out the reported sequence: Recruiter Screen, Technical Phone Screen, Virtual Onsite Loop, Behavioral and Leadership Round.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work Cisco Routers

  • Spend the session on Cisco Routers, which ALOIS candidates report being tested on.
  • Write one worked example in Cisco Routers and time yourself on it.

Deliverable: One timed worked example in Cisco Routers.

Day 3 — Work Cisco Switches

  • Spend the session on Cisco Switches, which ALOIS candidates report being tested on.
  • Write one worked example in Cisco Switches and time yourself on it.

Deliverable: One timed worked example in Cisco Switches.

Day 4 — Work Network Troubleshooting

  • Spend the session on Network Troubleshooting, which ALOIS candidates report being tested on.
  • Write one worked example in Network Troubleshooting and time yourself on it.

Deliverable: One timed worked example in Network Troubleshooting.

Day 5 — Answer out loud: Core Routing & Switching

  • Answer aloud, timed: Explain the difference between BGP and OSPF, and describe a scenario where you would use each.
  • Answer aloud, timed: How does Spanning Tree Protocol prevent network loops, and what are the differences between classic STP and RSTP?

Deliverable: Spoken answers to 2 reported Core Routing & Switching question(s), under time.

Day 6 — Answer out loud: Network Security & Firewalls

  • Answer aloud, timed: How do you configure a site-to-site IPsec VPN, and what are the common reasons Phase 1 might fail?
  • Answer aloud, timed: Explain the concept of NAT. How is it implemented differently on a Cisco ASA versus a Palo Alto firewall?

Deliverable: Spoken answers to 2 reported Network Security & Firewalls question(s), under time.

Day 7 — Answer out loud: Wireless & Enterprise Connectivity

  • Answer aloud, timed: How do you troubleshoot a user who is experiencing intermittent disconnects from the corporate Aruba wireless network?
  • Answer aloud, timed: Explain the role of a wireless LAN controller (WLC) in an enterprise environment.

Deliverable: Spoken answers to 2 reported Wireless & Enterprise Connectivity question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe a time you had to troubleshoot an asymmetric routing issue. How did you identify and resolve it?

Medium · Core Routing & Switching

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Tell me about a time you led a network gap analysis. What discrepancies did you find, and how did you address

Medium · Behavioral & Gap Analysis

Tell me about a time you led a network gap analysis. What discrepancies did you find, and how did you address them?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you ensure your network documentation and Visio diagrams are easily understood by junior engineers?

Medium · Behavioral & Gap Analysis

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a situation where you had to work with a team member who had a very different working style than your

Medium · Behavioral & Gap Analysis

Describe a situation where you had to work with a team member who had a very different working style than yours. How did you ensure the project succeeded?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

With 20% international travel required, tell me about your experience managing network deployments in foreign

Medium · Behavioral & Gap Analysis

With 20% international travel required, tell me about your experience managing network deployments in foreign or remote data centers.

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?