Zscaler Software Engineer
Interview Guide

• Write the URL-to-page walkthrough end to end: DNS resolution (stub resolver, recursive resolver, caching and TTL), the TCP three-way handshake, the TLS handshake, then the HTTP request. At each step, name the layer and the header fields involved.
• Add the MSS/MTU detail the reported question asks for: how MSS is derived from MTU, how path MTU discovery depends on ICMP, and why filtered ICMP causes connections that stall on large transfers.
• Answer TCP vs UDP and L4 vs L7 as choices with reasons: what each gives up, and what a device can decide when it sees only addresses and ports versus the full HTTP request.
• Practise the bank networking items Application Layer Protocols and IPv4 vs IPv6 and OSI.

Deliverable: A one-page layered diagram of a page load that you can redraw from memory, with the MSS/MTU and DNS steps annotated.

• Walk through the TLS 1.3 handshake (ClientHello with key share and SNI, ServerHello, encrypted certificate and CertificateVerify, Finished) and say where TLS 1.2 needs an extra round trip.
• Explain proxy interception as two TLS sessions. The proxy presents a certificate for the requested host, signed by an enterprise root CA the client trusts, and opens its own validated session to the origin. Name what breaks it, such as certificate pinning.
• Compare IPv4 and IPv6 headers: IPv6 has a fixed 40-byte header, no header checksum, no fragmentation by routers, extension headers and a flow label. If asked about collision avoidance, note that CSMA/CA is a link-layer mechanism before you answer.
• Diagnose a slow connection layer by layer with dig, traceroute and a packet capture, using the bank items TCP, DNS, Traceroute, and Wireshark and Networking, DNS, TLS, and PCAP.

Deliverable: A written triage order for DNS, TCP and TLS latency, and a two-session diagram of TLS interception.

• Solve Delete Odd Nodes in Linked List in place, drawing the pointer rewiring for lists of length 0, 1, 2 and 3 before you run the code.
• Implement Min Stack in O(1) with an auxiliary stack of minimums. Push onto it when the new value is less than or equal to the current minimum, so duplicate minimums survive a pop.
• Implement the LRU cache as a hash map into a doubly linked list with sentinel head and tail nodes, and test the eviction order after a get refreshes a key.
• Solve BST two-sum three ways: in-order into an array plus two pointers (O(n) time, O(n) space), a hash set during traversal, and forward and reverse in-order iterators (O(n) time, O(h) space). Check that the two values come from different nodes.
• Do one set of multiple-choice practice on OS, DBMS and networking fundamentals, since the online assessment is described as mixing these with coding.

Deliverable: Four working solutions, each with its complexity stated and a list of edge-case tests.

• Matrix shortest path: use DP only when moves are restricted to right and down. With four-way movement and obstacles, use BFS for unit cost or Dijkstra for non-negative weights. Say which case the prompt's rules create before you code.
• Cycle detection and topological sort: Kahn's algorithm with a min-heap gives the lexicographically smallest order, and emitting fewer than V nodes means there is a cycle. Practise the bank item Cycle Detection or Topological Sort.
• Longest common substring: dp[i][j] is the length of the common suffix ending at i and j, reset to 0 on a mismatch. It runs in O(mn) time and O(min(m, n)) space with a rolling row.
• Work the reviewed exercise Find peak concurrent sandbox usage from run intervals to practise sweep-line tie-breaks and handling of nulls.

Deliverable: Three graph or DP solutions plus the sweep-line exercise, each with the input bound that justifies its complexity.

• Explain virtual memory: page tables, the TLB, page faults, and what a context switch costs in cache and TLB state.
• Name the four deadlock conditions (mutual exclusion, hold and wait, no preemption, circular wait) and show prevention by breaking one of them, usually with a global lock order.
• Write a bounded producer-consumer queue with a mutex and two condition variables, waiting inside while loops, and contrast a mutex (ownership) with a counting semaphore (permits). This covers the bank item Multithreading and Producer-Consumer Coding.
• Language track. For C++: raw vs unique_ptr vs shared_ptr, a leak fixed with RAII, and a shared_ptr cycle broken with weak_ptr. For Java: the memory model, garbage collection and Spring transactions (bank item Java Microservices Transaction Handling).

Deliverable: A producer-consumer implementation that passes a stress test, and a one-page note for your language track.

• Practise the bank design item Design Global Metrics Monitoring and Real-Time Alerting. State the requirements, data model and hot path, and how the design fails. For related bank practice, try Design a Multi-Dimensional Job Rate Limiter or TTL and Data Pipeline with Rate Limiting.
• Work the reviewed exercises Specify webhook signature verification a customer can implement (HMAC, replay bounds, key rotation) and Migrate a live partitioned event table without blocking ingest (transactions and locks).
• Attempt the bank items Insert-Only Query with Hidden Updates and Transactions in Data Systems, stating the isolation level your answer assumes.
• Rehearse one past project at three depths so an interviewer can pull you to any level mid-answer.

Deliverable: One design write-up that includes its failure modes, and a project walkthrough you can deliver at three depths.

• Prepare stories for the reported prompts: a complex technical issue under a tight deadline, a difficult stakeholder or teammate, balancing IC work with mentoring, and why you are leaving your current role.
• Write a why-Zscaler answer tied to the work you would do (proxy, data plane, control plane or frontend), not to figures you cannot source.
• Set a compensation range from your own data points for the level and location before the HR conversation.
• Run a mock with a partner who interrupts and keeps their camera off, mixing one networking deep-dive, one coding problem and one behavioural prompt.
• Confirm the coding language with your recruiter, and ask whether preparation materials are available for your panel.

Deliverable: Four rehearsed stories, a why-Zscaler answer, and notes from one interrupted mock.