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Questions and Answers
What is the total number of bytes in the header of an IP packet if the HLEN value is 1000 in binary?
What is the total number of bytes in the header of an IP packet if the HLEN value is 1000 in binary?
If the HLEN value in an IP packet is 0101 in binary, how many bytes of options are being carried by this packet?
If the HLEN value in an IP packet is 0101 in binary, how many bytes of options are being carried by this packet?
What is the maximum Transmission Unit (MTU) for Ethernet data-link layer protocol?
What is the maximum Transmission Unit (MTU) for Ethernet data-link layer protocol?
If a router receives a packet larger than the MTU and the Do Not Fragment (DF) bit is set to 0, what action may the router take?
If a router receives a packet larger than the MTU and the Do Not Fragment (DF) bit is set to 0, what action may the router take?
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In IP packet fragmentation, what does the Fragmentation Offset indicate?
In IP packet fragmentation, what does the Fragmentation Offset indicate?
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When one network needs to transmit datagrams to a network with a smaller MTU, what strategy might it employ?
When one network needs to transmit datagrams to a network with a smaller MTU, what strategy might it employ?
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If an IP packet's total length field is 0000000000101000 in binary, how many bytes of data does this packet carry?
If an IP packet's total length field is 0000000000101000 in binary, how many bytes of data does this packet carry?
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Study Notes
Packet Fragmentation
- The first byte number is calculated by multiplying the offset value by 8.
- The total length of a packet includes the header length and the data length.
IPv6
- IPv6 was introduced to address the need for more addresses in the growing Internet.
- IPv6 uses 128-bit addresses, allowing for a much larger address space.
- IPv6 simplifies packet processing by only allowing packet fragmentation at the data source.
- Routers do not fragment packets in IPv6; instead, they send an ICMP error message and discard the packet if it's too big.
IPv6 Header Format
- The IPv6 header format is simplified from its IPv4 header.
- The length of the IPv6 header is 40 bytes.
- The version field is 4 bits and indicates the version of the Internet Protocol (0110 for IPv6).
- The maximum size of each fragment is the MTU minus the IP header size (20 bytes minimum; 60 bytes maximum).
Fragmentation and Reassembly
- A packet may be fragmented at one router and further fragmented at another router.
- A receiver knows a packet is a fragment if the "more fragments" flag is set or the fragment offset is nonzero.
- The "more fragments" flag is set for all fragments except the last one.
- The fragment offset is nonzero for all fragments except the first one.
Fragmentation Examples
- If the M bit is 0, it means there are no more fragments, and the packet is the last fragment.
- If the M bit is 1 and the offset value is 0, it is the first fragment.
- The number of the first byte can be calculated by multiplying the offset value by 8.
Maximum Transmission Unit (MTU)
- MTU is the maximum amount of data that a link-layer frame can carry.
- MTU differs from one data-link layer protocol to another (e.g., Token Ring, Ethernet).
- When a packet is too big for a network with a smaller MTU, it may be fragmented by the router.
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Description
Learn how to calculate the number of the first byte and last byte in an IPv6 packet based on offset, HLEN, and total length values. Understand how to determine the range of bytes in a packet. Practice calculating byte numbers in IPv6 packets.
