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BAI 513 – Introduction to Protocol Analysis

BAI 513 – Introduction to Protocol Analysis. Instructor: John Zabiuk W205, NAIT HP CENTER. Internet Protocol - IP. Workhorse of TCP/IP protocol suite All TCP, UDP, ICMP data get transmitted as IP packets Unreliable, connectionless packet delivery service

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BAI 513 – Introduction to Protocol Analysis

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  1. BAI 513 – Introduction to Protocol Analysis Instructor: John Zabiuk W205, NAIT HP CENTER

  2. Internet Protocol - IP • Workhorse of TCP/IP protocol suite • All TCP, UDP, ICMP data get transmitted as IP packets • Unreliable, connectionless packet delivery service • If something goes wrong, IP has a simple error handling algorithm: throw away packet and try to send an ICMP message back to the source • Reliability provided by the upper layers • Connectionless – Maintains no state information about successive datagrams

  3. IP HEADER – RFC 791

  4. IP HEADER (cont.) • Version Field – 4 bits • A 4-bit field identifying version of IP protocol used in creating datagram • 0100 indicates IP V4 • Internet Header Length (IHL) – 4 bits • A 4-bit field identifying length of header in 32-bit words • Minimum length of header is 20 bytes, max. is 24

  5. IP HEADER (cont.) • Type of Service (ToS) – 8 bits • Actually split into two fields (ToS and Precedence) indicating special handling of packet • R represents reserved (0) • ToS indicates datagram handling - Precedence represents priority • 0000 default -000 Routine • 0001 minimize monetary cost -001 Priority • 0010 maximize reliability -010 Immediate • 0100 maximize throughput -011 Flash • 1000 minimize delay -100 Flash Override • 1111 maximize security -101 Critic / ECP -110 Internetwork Control -111 Network Control

  6. IP HEADER (cont.) • Total Length – 16 bits • Field indicating total length of IP datagram (up to 65,535 bytes) • Identification – 16 bits • ID field enables each datagram or fragmented datagram to be identified • Flags – 3 bits • Contains 2 bits used to denote how fragmentation occurs, and another bit presently unassigned. • Bit 0 – Reserved • Bit 1 – Fragment (0 = allowed, 1 = not allowed) • Bit 2 – More fragments (0 = last fragment, 1 = more to come)

  7. IP HEADER (cont.) • Fragment Offset – 13 bits • If a datagram is fragmented, the fragment offset is a 13-bit field specifying the offset (in bytes) from beginning of header to beginning of fragment. It indicates where a fragment belongs in the complete message • Time-To-Live (TTL) – 8 bits • 8-bit filed specifying the maximum time that a datagram can exist • Commonly used as a hop-count field • Can be used to identify source operating system • 128 Windows 9x/NT/2000 • 60 AIX, Cisco IOS 11.2 • 255 Cisco IOS 12.0 • 64 Linux, Solaris

  8. IP HEADER (cont.) • Protocol – 8 bits • Identifies the higher layer protocol used to create the message • 1 ICMP • 2 IGMP • 6 TCP • 8 EGP • 9 Any private interior gateway (eg. CDP) • 17 UDP • 45 IDRP • 88 EIGRP • 89 OSPF • Refer to RFC 1700 for a complete list • Checksum – 16 bits • A checksum on the header only • Source IP Address – 32 bits • Destination IP Address – 32 bits

  9. IP HEADER (cont) • Checksum – 16 bits • A checksum on the header only • Source IP Address – 32 bits • Destination IP Address – 32 bits

  10. IP HEADER (cont.) • Options & Padding – 32 bits (optional) • Allows IP to support various options such as security • Loose Source Routing • Series pf router interface addresses listed which packet must pass through • Strict Source Routing • As above, but packet must pass only through listed addresses in order • Record Route • Records address of outgoing interfaces packets passes through • TimeStamp • As above but also lists time

  11. Your Turn! • IP LAB • Page 237 of Course Pack

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