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Internet Protocol V4

Internet Protocol V4. Reading: Chapter 14. A summary of IPV4 functions. Providing unreliable connectionless datagram service Defining IP packet format Defining IP addressing scheme Routing/forwarding IP packets across interconnected networks Preventing looping of IP packets

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Internet Protocol V4

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  1. Internet Protocol V4 Reading: Chapter 14 FSU CIS 5930 Internet Protocols

  2. A summary of IPV4 functions • Providing unreliable connectionless datagram service • Defining IP packet format • Defining IP addressing scheme • Routing/forwarding IP packets across interconnected networks • Preventing looping of IP packets • Fragmenting/reassembling IP packets FSU CIS 5930 Internet Protocols

  3. IP packet format 0 15 31 3 7 Version IHL TOSt/Codepoint Total length Identification D F Fragment Offset M F Time to Live Protocol Checksum Source address Destination address Optionen and payload IP packet header FSU CIS 5930 Internet Protocols

  4. Some fields • IHL: Internet Header Length • Multiple of 32 bits • Identification • Unique for each packet (generated at source) • Increased by 1 for each packet, normally • Checksum • Only covers the header part FSU CIS 5930 Internet Protocols

  5. IP address classes Class Host address range 0 31 8 16 24 A Host 0 Network 1.0.0.0 – 127.255.255.255 B Host 1 0 Network 128.0.0.0 – 191.255.255.255 C 1 1 0 192.0.0.0 – 223.255.255.255 Host Network D Multicast group addresses 1 1 1 0 224.0.0.0 – 239.255.255.255 E 1 1 1 1 0 Reserved 240.0.0.0 – 247.255.255.255 IP addresses • Classes in the original definition • A, B, C, D, E FSU CIS 5930 Internet Protocols

  6. Private addresses • Class A • 10.0.0.0 – 10.255.255.255 • Class B • 172.16.0.0 – 172.31.0.0 • Class C • 192.168.0.0 – 192.168.255.0 FSU CIS 5930 Internet Protocols

  7. Special addresses • 127.x.y.z • Loopback address • Host part == 0 • The network itself • Host part == 1 • All hosts in the network FSU CIS 5930 Internet Protocols

  8. Higher layers ip_input.c ip_output.c ip_queue_xmit ip_local_deliver MULTICAST IP_LOCAL_OUTPUT ip_mr_input . . . IP_LOCAL_INPUT ip_queue_xmit2 ip_forward.c IP_FORWARD ip_local_deliver ip_forward_finish ip_forward ip_output ip_fragment ip_finish_output ip_rcv_finish ROUTING ForwardingInformation Base IP_POST_ROUTING IP_PRE_ROUTING ip_route_input ip_rcv ip_finish_output2 ARP ARP neigh_resolve_output dev.c dev.c dev_queue_xmit net_rx_action Implementation of IP FSU CIS 5930 Internet Protocols

  9. Handling incoming packet • ip_rcv() • Drop packets that should not be processed • Correctness checking • NF_IP_PRE_ROUTING • ip_rcv_finish() • ip_rcv_finish() • Determining the route (ip_route_input()) • Processing options • Passing to the element that should further processes the packet, skb->dst->input() • ip_local_deliver() • ip_forward() • ip_mr_input() FSU CIS 5930 Internet Protocols

  10. Forwarding packets • ip_forward() • Some sanity checking (e.g., TTL) • ICMP to source if dropping pkts because of TTL • Making sure having enough space • Fragmentation related processing • NF_IP_FORWARD • ip_forward_finish() • ip_forward_finish() • Processing IP options • ip_send() • Ip_send() • Fragmenting if necessary • Ip_finish_output() FSU CIS 5930 Internet Protocols

  11. Forwarding IP packets • ip_finish_output() • Preparing something for layer 2 • Pointing the network device • Indicating the packet type (IP) • NF_IP_POST_ROUTING • ip_finish_output2() • ip_finish_output2() • Passing to the lower layer (e.g., dev_queue_xmit()) FSU CIS 5930 Internet Protocols

  12. Delivering packets locally • ip_local_deliver() • Reassembling fragmented IP packets • NF_IP_LOCAL_IN • ip_local_deliver_finish() • ip_local_deliver_finish() • Demultiplexing to other (upper) layers • Tcp_v4_rcv() • Udp_rcv() • Icmp_rcv() • Igmp_rcv() • ICMP packets generated if dropping packet FSU CIS 5930 Internet Protocols

  13. inet_protocol udp_rcv() 0 inet_protos[MAX_INET_PROTOS] handler udp_err() err_handler next inet_protocol protocol: IPPROTO_UDP copy data name: "UDP" inet_protocol igmp_rcv() 1 handler Null err_handler next protocol:IPPROTO_IGMP copy data name: "IGMP" MAX_INET_PROTOS inet_protocol Demultiplexing IP packets FSU CIS 5930 Internet Protocols

  14. Some management functions • inet_add_protocol() • inet_del_protocol() • Some useful functions • in_ntoa() • IP address to dotted decimal format • in_aton() • Dotted decimal format to IP address FSU CIS 5930 Internet Protocols

  15. Transport-layer packets • ip_queue_xmit() • Determining route • Ip_route_output() if no route yet • Filling fields of header • Adding option field if there is • NF_IP_LOCAL_OUT • ip_queue_xmit2() • ip_queue_xmit2() • Some sanity check • Enough buffer space to hold packet • Setting output network device, dst • Dst->output(), ip_output() FSU CIS 5930 Internet Protocols

  16. net_device name: eth1 dev_base ... Network Layer . . . net_device in_device name: eth0 ip_ptr state next in_ifaddr ... Hardware in_device ip_mc_list MAC layer dev Network layer . . . refcnt lock ip_ptr in_ifaddr in_ifaddr dead ifa_list ip_mc_list mc_list mr_v1_seen arp_parms . . . ip_mc_list cnf ipv4_devconf neigh_parms Data of IP instance FSU CIS 5930 Internet Protocols

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