Header Length in IPv4

Duration: 5 min

This video lesson is available to enrolled students.

Return to /learn/DSSSB-TGT-COMPUTER-SCIENCE-COMPLETE-COURSE/computer-network/net-layer-ipv4-proto/net-layer-ipv4-basics/asset-header-length-in-ipv4 after enrolling

Inside: a video lesson and guided study material.

Module outline

  1. About Course: About the Course
  2. Section A: General Awareness: Polity, Physics, Biology, Chemistry, Static General Knowledge, History, Geography, Indian Economy, GK- Current Affairs, Evolution of Indian Banking (Banking & Financial Awareness), Environment
  3. Section A: General Intelligence & Reasoning ability: Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Data Sufficiency, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Analytical Reasoning (Counting Figures Reasoning), Blood Relations, Syllogisms, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Seating Arrangements, Directions (Direction Test), Puzzle Solving (Puzzles), Calendar, Clock, Cubes & Dices, Selection Decision Table (Decision Making), Logical Sequence Of Words, Crypt Arithmetic, Venn Diagram, Data Arrangement, Inequality, Analogy, Ranking, Order and Sequence, TCS NQT Advanced Reasoning Ability
  4. Section A: Arithmetical & Numerical Ability: Ratio and Proportion (Ratios), Divisibility Rules, Data Interpretation, Mixture and Alligation, Permutation and Combination, Logarithm, Number System, HCF LCM, Sequence and Series (Series), Speed Time and Distance, Percentage, Average, Profit and Loss, Simple Interest and Compound Interest, Time and Work, Pipe and Cistern, Mensuration and Geometry, Powers and Exponents (Surds and Indices), Algebra, Probability, Mental Ability, Age Problems, Partnership, Statistics, Arithmetic, Speed Mathematics and Basic Mathematics, Miscellaneous
  5. Section A: English Language & Comprehension: Vocabulary, Subject Verb Agreement (Verb Noun Agreement), Adjectives, Tenses, Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions), Articles, Sentence Construction, Preposition, Direct and Indirect Speech, Sentence Completion (Fill in the blanks), Sentence Re-arrangements (Para Jumbles) (Narrative Sequencing), Modals, Active Passive Voice (Voice), Sentence Correction (Error Correction), Adverb, Conjunction, Cloze Test (Cloze Passage)
  6. Section A: Hindi Language & Comprehension: भाषा, लिपि, ध्वनि, वर्ण, अक्षर, स्वर, व्यंजन, मात्रा और संयुक्ताक्षर, वर्तनी, वर्ण-विन्यास, अनुस्वार, अनुनासिक, चंद्रबिंदु और ‘र’ के रूप, शब्द, पद और शब्द-भेद, संज्ञा और सर्वनाम, विशेषण और क्रिया, लिंग, वचन, पुरुष और कारक, काल, वाच्य, वाक्य और वाक्य-भेद, संधि, समास, विलोम शब्द, पर्यायवाची शब्द, सामान्य अशुद्धियाँ, अनेक शब्दों के लिए एक शब्द, मुहावरे और लोकोक्तियाँ, अपठित गद्यांश और अपठित पद्यांश, Multi-Topic Content (Cross-Concept Material), वर्णमाला
  7. Section B: Programming, Data Structures, OOP & Java: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling, Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, Java, OOPS with C++, Language Design, Intro to Compilers, Visual Basics, Syntax Analysis: Bottom-Up, Object Oriented Technology
  8. Section B: Computer Networks, TCP/IP & Network Security: Introduction to CN, Data Communication, DLL: Flow Control, DLL: Access Control, DLL: Error Control, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics, Network Access Technologies, Network Security, Society, Law & Ethics, Mobile Computing, Net Layer:Routing Protocol, Cyber Safety and Security
  9. Section B: Teaching Methodology: Child Development, Concept of Pedagogy, Theories, Inclusive Education, Experiential Pedagogy, Assessment & Evaluation, Curriculum Framework & Reforms, National Education Policy (NEP) 2020, Psychology, Teaching-Learning Process, Personality Development, Teaching Methods & Strategies, Learning and Motivation, Learners & Learning Process, Factors Affecting Teaching, Methods of Teaching, Nature, Objectives & Characteristics of Teaching, Teaching-Learning Aids & ICT Integration, Classroom Management & Communication, Evaluation, Assessment & Measurement, Curriculum & School Environment, Inclusive Education & Special Needs, Professional Development & Ethics
  10. Section B: Digital Electronics / Boolean Logic: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation, Analog-Digital Conversion
  11. Section B: Operating Systems & Linux: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, File Management, Disc Scheduling, Unix OS, Linux OS, Distributed Systems, Windows OS
  12. Section B: Data Base Management System: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, Relational Algebra, SQL, File Organization & Indexing, Transaction Management, Concurrency Control, Database Security & Authorization, Database Recovery, Data Warehousing & Mining
  13. Section B: Internet & Web Technologies: Website, Browser & Services, Internet Fundamentals, Web Design & Development, Protocols & Services, Web Publishing & Hosting, Server Side & Security, HTML Basics, CSS, Emerging Technologies, JavaScript-Basics, .Net Programming, Electronic Data Interchange and E-Commerce, XML
  14. Section B: Computer Fundamentals, IT Basics & Architecture: Basics of COA, Cache Memory Organization, Input Output Organisation, Register Transfer and Microoperations, Control Unit Design, Programming the Basic Computer, Terms & Abbreviations, MS Office Applications, Instr Formats & Modes, Floating Point Rep
  15. Section B: Python Language: Introduction to Python, Tokens, Variables, Data Types, I/O, Operators & Expressions, Control Flow & Looping, Collections & Strings, Functions & Modules, File Handling & Data Analysis
  16. Section B: Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management, extras, Fundamentals of Systems and Information Systems
  17. Section B: Design & Analysis of Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos, Advanced Algorithms
  18. Section B: Mathematics: Linear Algebra, Calculus, Trigonometry, Vectors, Set Theory, Functions, Relations, Propositional and Predicate Logic, Research Process Steps, Graph Theory
  19. Section B: Computer Graphics, Multimedia & Mobile Computing: Basics of Computer Graphics, 2-D Geometrical Transforms and Viewing, 3-D Object Representation, Geometric Transformations and Viewing, Multimedia
  20. Section B: Emerging Trends: Emerging Tech Trends, Knowledge Representation, Natural Language Processing
  21. DSSSB Previous Year Paper:
  22. Business Studies and Management: Business Communication, Business Organization and Management, Financial Accounting, Business Economics, Management Information System (MIS), Knowledge Management & New Economy
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture explains the Header Length (HLEN) field in an IPv4 datagram. The instructor presents a slide titled “Header Length” and uses the standard IPv4 header diagram/table to show that HLEN is a 4-bit field. Because the IPv4 header has a variable length due to optional fields, HLEN does not store the byte count directly. Instead, it stores the total header length measured in 32-bit words, or 4-byte units. The instructor emphasizes the scaling factor: to place a value in HLEN, divide the total header length in bytes by 4; at the receiver, multiply the HLEN value by 4 to recover the header length in bytes. A worked example is shown repeatedly: if HLEN contains decimal 5, represented as binary 0101, then header length = 5 × 4 = 20 bytes. The instructor also connects this to the header structure: the fixed part of the IPv4 header is 20 bytes, while Options + padding can add up to 40 bytes. Therefore the total IPv4 header length ranges from 20 to 60 bytes, and the corresponding HLEN field values range from 5 to 15. The final section reinforces this by mapping HLEN value 5 to 20 bytes and HLEN value 15 to 60 bytes, with on-screen notes such as “The length of IP header always lies in the range of [20 bytes, 60 bytes]” and “The range of header length field value is always [5, 15].”

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The lecture introduces the IPv4 Header Length (HLEN) field using a slide titled “Header Length” and an IPv4 header diagram. The instructor explains that HLEN is a 4-bit field and that the IPv4 datagram has a variable-length header. The key rule shown is that HLEN defines the total length of the datagram header in 4-byte words, so a scaling factor is used: divide the byte length by 4 to store it in HLEN. The on-screen example states that if the header length field contains decimal value 5, represented as binary 0101, then Header length = 5 × 4 = 20 bytes. The instructor points to the HLEN field and writes binary values next to it, reinforcing that 0101 corresponds to decimal 5.

  2. 2:00 – 5:00 02:00-05:00

    The instructor continues with the same “Header Length” slide and expands the explanation to the full IPv4 header table. The table shows fields such as VER, HLEN, Service type, Identification, Flags, Time-to-live, Protocol, Source IP address (32 bits), Destination IP address (32 bits), and a highlighted row for “Options + padding (0 to 40 bytes).” The instructor points from the HLEN area toward other header fields, including “Flags 3 bits” and “Header checksum 16 bits,” while handwritten notes appear on the board, including binary values such as “0 1 0 1” and “1 1 1 1 (15)” along with notes like “60 15.” This section connects the HLEN scaling rule to the variable options field: because options can add up to 40 bytes, the header length is not fixed at 20 bytes but can increase up to 60 bytes.

  3. 5:00 – 5:27 05:00-05:27

    The final segment summarizes the allowed range of IPv4 header lengths. A slide titled “Point to Note” states that the length of an IP header always lies in the range [20 bytes, 60 bytes]. The instructor derives the minimum as 5 × 4 = 20 bytes and the maximum as 20 + 40 = 60 bytes, where 40 bytes is the maximum options plus padding. The on-screen text also states that the range of header length field values is always [5, 15], because 20/4 = 5 and 60/4 = 15. The instructor writes a mapping on the whiteboard from HLEN values 5 through 15 to byte lengths 20 through 60, consolidating the scaling-factor rule into a compact exam-ready result.

The central concept is that IPv4 HLEN stores header length in 32-bit words, not bytes. The fixed IPv4 header is 20 bytes, which corresponds to HLEN = 5 because 20/4 = 5. Since Options + padding may add up to 40 bytes, the maximum header length is 60 bytes, corresponding to HLEN = 15 because 60/4 = 15. The lecture’s main method is the scaling factor: divide by 4 to encode, multiply by 4 to decode. The worked example HLEN = 5 → 20 bytes is used repeatedly, and the final takeaway is the range relationship: HLEN values [5, 15] correspond to header lengths [20, 60] bytes. This is likely important for exams because students must remember both the unit (4-byte words) and the resulting minimum/maximum values.

Loading lesson…