Total Length Field in IPv4

Duration: 5 min

This video lesson is available to enrolled students.

Return to /learn/HEXAWARE-PREPARATION/computer-networks/net-layer-ipv4-proto/net-layer-ipv4-basics/asset-total-length-field-in-ipv4 after enrolling

Inside: a video lesson and guided study material.

Module outline

  1. Quantitative Ability: Speed Mathematics and Basic Mathematics, Percentage, Ratio and Proportion (Ratios), Average, Profit and Loss, Simple Interest and Compound Interest, Time and Work, Pipe and Cistern, Speed Time and Distance, Number System, HCF LCM, Data Interpretation, Age Problems, Mixture and Alligation, Partnership, Algebra, Sequence and Series (Series), Mensuration and Geometry, Arithmetic
  2. Reasoning Ability: Puzzle Solving (Puzzles), Seating Arrangements, Coding Decoding, Blood Relations, Directions (Direction Test), Syllogisms, Data Sufficiency, Ranking, Order and Sequence, Series (Number and Letter Series) (Numerical Relations and Reasoning), Logical Sequence Of Words, Calendar, Clock, Cubes & Dices, Analytical Reasoning (Counting Figures Reasoning), Data Arrangement, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning)
  3. Verbal Ability: Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions), Cloze Test (Cloze Passage), Sentence Re-arrangements (Para Jumbles) (Narrative Sequencing), Vocabulary, Sentence Completion (Fill in the blanks), Active Passive Voice (Voice), Direct and Indirect Speech, Subject Verb Agreement (Verb Noun Agreement), Tenses, Preposition, Articles, Sentence Correction (Error Correction)
  4. Programming Basics (MCQs + Interview): C Programming by Yash Sir, Programming in C++, Java, Python for Placements by Yash Sir
  5. OOPs (MCQs + Interview): Object Oriented Programming (OOPS)
  6. DBMS (MCQs + Interview): Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Transaction Management, Decomposition Properties & 4NF, Concurrency Control, Database Recovery, File Organization & Indexing, Relational Algebra, Database Security & Authorization
  7. SQL (MCQs + Interview): SQL
  8. Operating Systems (MCQs + Interview): Introduction to OS, Process Management, CPU Scheduling, Deadlock, Threads & Process Creation, Memory Management, Virtual Memory, Process Synchronization, Disc Scheduling, File Management, Security
  9. Computer Networks (MCQs + Interview): Introduction to CN, Data Communication, DLL: Access Control, DLL: Flow Control, DLL: Error Control, DLL: Framing, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Net Layer:Routing Protocol, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics, Network Security, Mobile Technology, Cloud Computing and IoT, Cyber and Info Security
  10. Coding: Coding Questions by Yash Sir
  11. HR Interview: MR & HR Interview Preparation
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture explains the IPv4 Total Length field and its relationship to Maximum Transfer Unit (MTU) constraints. The instructor defines Total Length as the combined size of the IP header and data payload in bytes, noting it is a 16-bit field. The minimum datagram length is 20 bytes (header only, no data), while the maximum is 65,535 bytes, derived from the formula 2^16 - 1. The instructor writes and emphasizes the key formula: Length of data = Total length - (HLEN × 4), where HLEN is the header length in 32-bit words. The lecture then transitions to MTU, explaining that each link-layer protocol has a maximum payload size for encapsulated datagrams. A comparison table lists MTU values: Hyperchannel (65,535), Token Ring 16 Mbps (17,914), FDDI (4,352), Ethernet (1,500), and PPP (296). A diagram shows an IP datagram encapsulated within a frame payload, illustrating that the total datagram size must not exceed the link's MTU. This establishes why IP fragmentation may be necessary when a datagram exceeds the next-hop link's MTU.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The instructor introduces the Total Length field, stating on slide that it 'defines the total length (header plus data) of the IP datagram in bytes.' Two key bullets appear: 'Minimum total length of datagram = 20 bytes (20 bytes header + 0 bytes data)' and 'Maximum total length of datagram = Maximum value of 16-bit word = 65535 bytes.' An IPv4 header table is displayed on the right, listing fields including VER (4 bits), HLEN (4 bits), Service type (8 bits), Total length (16 bits), Identification (16 bits), Flags (3 bits), Fragmentation offset (13 bits), Time-to-live (8 bits), Protocol (8 bits), Header checksum (16 bits), Source/Destination IP address (32 bits each), and Options + padding (0 to 40 bytes). The instructor gestures toward the Total length cell while explaining its significance.

  2. 2:00 – 5:00 02:00-05:00

    The instructor writes the formula 'Length of data = total length - (HLEN) × 4' on the board, circling the HLEN term to emphasize that header length is measured in 32-bit words. Handwritten working shows '16 → = 2^16 − 1 =' with the result '65535' written to demonstrate the maximum value calculation. The lecture then transitions to Maximum Transfer Unit (MTU). A new slide states 'Each link-layer protocol has its own frame format' and that one feature is 'the maximum size of the payload that can be encapsulated.' A table compares MTU values: Hyperchannel 65,535; Token Ring (16 Mbps) 17,914; FDDI 4,352; Ethernet 1,500; and PPP 296. A diagram on the right shows an IP datagram (Header + Payload) inside a frame, labeled 'MTU: Maximum size of frame payload.' The instructor points to the Ethernet and FDDI rows, highlighting that when a datagram is encapsulated in a frame, its total size must be less than the MTU.

  3. 5:00 – 5:15 05:00-05:15

    The final sampled frame returns to the Total Length slide, showing the text 'It defines the total length (header plus data) of the IP datagram in bytes.' This appears to be a recap or transition point, reinforcing the core definition before potentially moving to fragmentation. The MTU table and encapsulation diagram remain visible in earlier frames of this window, confirming the connection between Total Length constraints and link-layer MTU limits.

The lecture builds a logical progression from field definition to practical constraint. First, Total Length is defined as a 16-bit field measuring header plus data in bytes, with bounds of 20 to 65,535. The formula Length of data = Total length - (HLEN × 4) provides the method to compute payload size from header parameters. The MTU section then introduces a critical real-world constraint: while IP allows datagrams up to 65,535 bytes, individual links (especially Ethernet at 1,500 bytes) impose much smaller maximum payload sizes. The encapsulation diagram visually connects these concepts, showing that an IP datagram must fit within a frame's payload limit. This sets up the necessity of fragmentation when a datagram exceeds the next-hop MTU, though fragmentation itself is not explicitly covered in the sampled windows. Key exam points: remember HLEN is in 32-bit words (multiply by 4 for bytes), minimum datagram is 20 bytes, and Ethernet's 1,500-byte MTU is the most commonly tested value.

Loading lesson…