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UDP and IP Fragment

UDP and IP Fragment. RedBeanZ 02 오효식. UDP - Outline. User Datagram Protocol Layer 4, Transport Layer Protocol Differences of UDP from TCP UDP does not guarantee delivery of packets UDP is instead known as a “ fire and forget ” protocol

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UDP and IP Fragment

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  1. UDP and IP Fragment RedBeanZ 02 오효식

  2. UDP - Outline • User Datagram Protocol • Layer 4, Transport Layer Protocol • Differences of UDP from TCP • UDP does not guarantee delivery of packets • UDP is instead known as a “fire and forget” protocol • UDP is also referred to as ‘connectionless protocol’ • Faster than TCP

  3. UDP - Structure • UDP only has 8bytes header,4fields (TCP – 14fields, 20bytes) • UDP Data size has variable length IP Datagram UDP Datagram 20bytes 8bytes

  4. UDP – Structure (Cont.) • Source Port - 16 bits • Destination Port - 16 bits • Length - 16 bits • The length in bytes of the UDP header and the encapsulated data • Checksum - 16 bits

  5. UDP – Application • Using UDP protocol to take advantage of the lower overhead • But, UDP application should to has the function of reassemble. • DNS(Domain Name System), TFTP(Trivial FTP), SNMP(Simple Network Management Protocol).. ETC

  6. IP Fragment • Datagrams can be fragmented into pieces small enough to pass over a link with a smaller MTU than the original datagram size. • The Datagram pieces are reassembled at the last destination. • MTU - Maximum Transfer Unit • Ethernet 1,500 bytes • Token Ring (16 Mbps) 17,914 bytesToken Ring (4 Mbps) 4,464 bytes

  7. IP Fragment - Example EX)Ethernet : 1500-28(IP헤더+UDP헤더) = 1472(allowable maximum data size) IP Datagram 20bytes 8bytes 20bytes 1byte 20bytes 8bytes 1472bytes Packet Packet IP Fragment

  8. IP Fragment - Fields

  9. IP Fragment – Fields (Cont.)

  10. IP Fragment – ICMP Error • If a router tries to forward an IP datagram, with the DF bit set, • MTU < the size of the packet : the router will drop the packet and return an Internet Control Message Protocol (ICMP) "Destination Unreachable" • When the source station receives the ICMP message, we should choose the smaller segment size. • Through that way, We can find the “path MTU”

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