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The Network Layer

The Network Layer. Chapter 5. The IP Protocol. The IPv4 (Internet Protocol) header. IP datagram format. IP protocol version number. 32 bits. total datagram length (bytes). header length (bytes). type of service. head. len. ver. length. for fragmentation/ reassembly. fragment

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The Network Layer

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  1. The Network Layer Chapter 5

  2. The IP Protocol The IPv4 (Internet Protocol) header.

  3. IP datagram format IP protocol version number 32 bits total datagram length (bytes) header length (bytes) type of service head. len ver length for fragmentation/ reassembly fragment offset “type” of data flgs 16-bit identifier max number remaining hops (decremented at each router) upper layer time to live Internet checksum 32 bit source IP address 32 bit destination IP address upper layer protocol to deliver payload to E.g. timestamp, record route taken, specify list of routers to visit. Options (if any) data (variable length, typically a TCP or UDP segment)

  4. IP Addresses IP address formats.

  5. IP Addresses (2) Special IP addresses.

  6. Subnets A campus network consisting of LANs for various departments.

  7. Subnets (2) A class B network subnetted into 64 subnets.

  8. CDR – Classless InterDomain Routing 5-59 A set of IP address assignments.

  9. NAT – Network Address Translation Placement and operation of a NAT box.

  10. The TCP Segment Header TCP Header.

  11. NAT – Network Address Translation Placement and operation of a NAT box.

  12. Internet Control Message Protocol 5-61 The principal ICMP message types.

  13. ICMP: Internet Control Message Protocol used by hosts & routers to communicate network-level information error reporting: unreachable host, network, port, protocol echo request/reply (used by ping) network-layer “above” IP: ICMP msgs carried in IP datagrams ICMP message: type, code plus first 8 bytes of IP datagram causing error TypeCodedescription 0 0 echo reply (ping) 3 0 dest. network unreachable 3 1 dest host unreachable 3 2 dest protocol unreachable 3 3 dest port unreachable 3 6 dest network unknown 3 7 dest host unknown 4 0 source quench (congestion control - not used) 8 0 echo request (ping) 9 0 route advertisement 10 0 router discovery 11 0 TTL expired 12 0 bad IP header

  14. Traceroute and ICMP Source sends series of UDP segments to dest First has TTL =1 Second has TTL=2, etc. Unlikely port number When nth datagram arrives to nth router: Router discards datagram And sends to source an ICMP message (type 11, code 0) Message includes name of router& IP address When ICMP message arrives, source calculates RTT Traceroute does this 3 times Stopping criterion UDP segment eventually arrives at destination host Destination returns ICMP “host unreachable” packet (type 3, code 3) When source gets this ICMP, stops.

  15. ARP– The Address Resolution Protocol Three interconnected /24 networks: two Ethernets and an FDDI ring.

  16. Dynamic Host Configuration Protocol Operation of DHCP.

  17. The IP Protocol The IPv4 (Internet Protocol) header.

  18. The Main IPv6 Header The IPv6 fixed header (required).

  19. Extension Headers 5-69 IPv6 extension headers.

  20. Extension Headers (2) The hop-by-hop extension header for large datagrams (jumbograms).

  21. Extension Headers (3) The extension header for routing.

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