1. FSU CIS 5930 Internet Protocols
Internet Protocol V4
Reading: Chapter 14
Fall 2004
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
Targets: adaptive, reaching the destination even if there is some failure along a path.
Operating on different network technology (IP addressing).
Some basic concepts in IP first: IP header
Fall 2004
FSU CIS 5930 Internet Protocols

3. FSU CIS 5930 Internet Protocols
IP packet header
Version
IHL
TOSt/Codepoint 3 7 15 31
IP packet format
Total length
Identification F D M
Fragment Offset
Time to Live
Protocol
Checksum
Source address
Destination address
Optionen and payload
Fall 2004
FSU CIS 5930 Internet Protocols

4. FSU CIS 5930 Internet Protocols
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
Fall 2004
FSU CIS 5930 Internet Protocols

5. IP addresses Classes in the original definition A, B, C, D, E
Host
Network
1 0
1 1 0
Multicast group addresses
Reserved A B C D E
Class 8 16 24 31
IP address classes – – – – –
Host address
range
Fall 2004
FSU CIS 5930 Internet Protocols

6. FSU CIS 5930 Internet Protocols
Private addresses
Class A –
Class B –
Class C –
Fall 2004
FSU CIS 5930 Internet Protocols

7. FSU CIS 5930 Internet Protocols
Special addresses
127.x.y.z
Loopback address
Host part == 0
The network itself
Host part == 1
All hosts in the network
Fall 2004
FSU CIS 5930 Internet Protocols

8. neigh_resolve_ output
Implementation of IP
ARP
ip_input.c
MULTICAST
ip_rcv
ip_forward.c
Higher layers
dev.c
net_rx_action
ip_rcv_finish
IP_PRE_ROUTING
ip_forward
ip_forward_finish
ip_local_deliver
IP_LOCAL_INPUT
ip_mr_input
IP_FORWARD
ip_output.c
ip_finish_output2
ip_output
IP_POST_ROUTING
ip_queue_xmit2
IP_LOCAL_OUTPUT
ip_queue_xmit
ip_finish_output
. . .
dev_queue_xmit
neigh_resolve_ output
ROUTING
Forwarding Information Base
ip_route_input
ip_fragment
Fall 2004
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()
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()
Fall 2004
FSU CIS 5930 Internet Protocols

10. FSU CIS 5930 Internet Protocols
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()
Processing IP options
ip_send()
Ip_send()
Fragmenting if necessary
Ip_finish_output()
Fall 2004
FSU CIS 5930 Internet Protocols

11. FSU CIS 5930 Internet Protocols
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()
Passing to the lower layer (e.g., dev_queue_xmit())
Fall 2004
FSU CIS 5930 Internet Protocols

12. Delivering packets locally
ip_local_deliver()
Reassembling fragmented IP packets
NF_IP_LOCAL_IN
ip_local_deliver_finish()
Demultiplexing to other (upper) layers
Tcp_v4_rcv()
Udp_rcv()
Icmp_rcv()
Igmp_rcv()
ICMP packets generated if dropping packet
Fall 2004
FSU CIS 5930 Internet Protocols

13. Demultiplexing IP packets
handler
err_handler
next
protocol: IPPROTO_UDP
inet_protocol
copy
data
name: "UDP"
protocol:IPPROTO_IGMP
name: "IGMP"
udp_rcv()
udp_err()
igmp_rcv()
Null
inet_protos[MAX_INET_PROTOS] 1
MAX_INET_ PROTOS
Fall 2004
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
Fall 2004
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()
Some sanity check
Enough buffer space to hold packet
Setting output network device, dst
Dst->output(), ip_output()
Fall 2004
FSU CIS 5930 Internet Protocols

16. FSU CIS 5930 Internet Protocols
Data of IP instance
dev
refcnt
lock
dead
in_device
ifa_list
mc_list
mr_v1_seen
in_ifaddr
dev_base
name: eth0
state
next
net_device
...
Hardware
MAC layer
Network layer
. . .
name: eth1
ip_ptr
Network Layer
arp_parms
cnf
ipv4_devconf
ip_mc_list
neigh_parms
Fall 2004
FSU CIS 5930 Internet Protocols