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Internet Protocol V4
Reading: Chapter 14
Fall 2004
FSU CIS 5930 Internet Protocols
1
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
Fall 2004
FSU CIS 5930 Internet Protocols
2
IP packet header
IP packet format
0
3
Version
15
7
IHL
Total length
TOSt/Codepoint
D
F
Identification
Time to Live
31
M
F
Fragment Offset
Checksum
Protocol
Source address
Destination address
Optionen and payload
Fall 2004
FSU CIS 5930 Internet Protocols
3
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
4
IP addresses
• Classes in the original definition
– A, B, C, D, E
IP address classes
Class
0
A
B
C
D
E
Fall 2004
8
16
110
1110
11110
Host address
range
128.0.0.0 –
191.255.255.255
Host
Network
10
31
1.0.0.0 –
127.255.255.255
Host
Network
0
24
Host
Network
192.0.0.0 –
223.255.255.255
Multicast group addresses
224.0.0.0 –
239.255.255.255
Reserved
240.0.0.0 –
247.255.255.255
FSU CIS 5930 Internet Protocols
5
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
Fall 2004
FSU CIS 5930 Internet Protocols
6
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
7
Implementation of IP
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_forward.c
IP_FORWARD
ip_queue_xmit2
ip_local_deliver
ip_forward
ip_rcv_finish
ROUTING
IP_PRE_ROUTING
Forwarding
Information Base
ip_rcv
ip_route_input
ip_forward_finish
ip_output
ip_fragment
ip_finish_output
IP_POST_ROUTING
ip_finish_output2
ARP
ARP
neigh_resolve_
output
dev.c
dev_queue_xmit
net_rx_action
Fall 2004
dev.c
FSU CIS 5930 Internet Protocols
8
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()
Fall 2004
FSU CIS 5930 Internet Protocols
9
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()
Fall 2004
FSU CIS 5930 Internet Protocols
10
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())
Fall 2004
FSU CIS 5930 Internet Protocols
11
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
Fall 2004
FSU CIS 5930 Internet Protocols
12
Demultiplexing IP packets
inet_protocol
0
inet_protos[MAX_INET_PROTOS]
handler
udp_rcv()
udp_err()
err_handler
next
inet_protocol
protocol: IPPROTO_UDP
copy
data
name: "UDP"
inet_protocol
1
handler
igmp_rcv()
Null
err_handler
next
protocol:IPPROTO_IGMP
copy
data
name: "IGMP"
MAX_INET_
PROTOS
Fall 2004
inet_protocol
FSU CIS 5930 Internet Protocols
13
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
14
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()
Fall 2004
FSU CIS 5930 Internet Protocols
15
Data of IP instance
net_device
name: eth1
dev_base
...
net_device
Network Layer
name: eth0
ip_ptr
...
in_device
state
next
in_ifaddr
...
Hardware
MAC layer
Network layer
ip_ptr
...
in_device
ip_mc_list
dev
refcnt
lock
dead
in_ifaddr
in_ifaddr
ifa_list
mc_list
ip_mc_list
mr_v1_seen
arp_parms
ip_mc_list
...
cnf
ipv4_devconf
Fall 2004
FSU CIS 5930 Internet Protocols
neigh_parms
16