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Application

Presentation

Session

Transport

Network

Datalink

Physical

OSI model

7

6

5

4

3

2

1

Application

IPv4, IPv6

DeviceDriver

Hardware

TCP UDP

Internet protocolsuite

Sockets

XTI

Userprocess

kernel

Application

details

Communicationsdetails

Raw SocketsDatalinkAccess

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Raw Sockets

Usage

Creation. Output. Input

Ping

Traceroute

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version

header

length type of service total length

identification 0D

F

M

Ffragment offset

32-bit source IPv4 address

32-bit source IPv4 address

options (if any)

data

time to live protocol header checksum

3 4 7 8 5 6 3

20 bytes

Raw Socket Usage

1 ICMP2 IGMP6 TCP17 UDP

1. R/W ICMPv4. IGMPv4. ICMPv6

ex. Ping

2. R/W other datagrams not processed by kernel

ex. Gated => implement OSPF (protocol = 89)

3. Build ones own IPv4 Header

ex. traceroute

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RawSocketCreation

Sockfd = socket ( AF_INET,

SOCK_RAW, protocol)

Set IP_HDRINCL socket option

If (setsockopt(sockfd, IPPROTO_IP,

IP_HDRINCL, &on, sizeof (on))>0)

error ;

BIND

No port

number

concept

CONNECT

No port

number

concept

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Raw Socket Output

1. Sendto / sendmsg+ destination IP

connect => write / writev / send

2. Starting Address for the kernel to write

Starting Addr. = First byte following the IP header

Set IP_HDRINCL =>

Starting Addr. = First byte of the IP header

3. Fragmentationby kernel

Kernel

Raw SocketsChecksum:

IPv4 => By Application

IPv6 => By Kernel

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Raw Socket Input

1. UDP / TCP Never pass to Raw Socket2. Most ICMP Kernel => Raw Socket

3. All IGMP Kernel => Raw Socket

4. All Unknown IP Datagram

Kernel ~> Raw Socket

5. Fragment In Reassemble ~> Raw Socket

Kernel

Raw Sockets

protocol field

bound addr. = dest. IP

connected addr. = source IP

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main

readloop

recvfrom proc_v4

proc_v6

sig_alrm

send_v4

send_v6

or

or

Infinite receive loop Send an echo requestonce a second

Overview ofPing

Establish signal handlerfor SIGALRM

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Traceroute with TTL Mechanism

TTL=1

ICMP

Router

A(Local)

B(Remote)

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Example of Traceroute

Solaris # traceroute gemini.tuc.noao.edu

traceroute to gemini.tuc.noao.edu (140. 252. 3. 54): 30 hops max, 12

data bytes

1 gw.kohala.com (206.62.226.62) 3.839ms 3.595ms 3.722ms2 tuc -1 -s1 -9 .rtd.net (206.85.40.73) 40.014ms 21.078ms 18.826ms

3 frame -gw.ttn.ep.net (198.32.152.9) 39.283ms 24.598ms 50.037ms

...7 gemini.tuc.noao.edu (140.252.3.54) 70.476ms 43.555ms 88.716ms

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Datalink Access

Usage

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Datalink Access

Watch packets received by datalink layer

ex. Tcpdumpon normal computer systems=> watch all packets on the local cable

Run certain programs as normal applications

instead of part of the kernelex. RARP (R/W over datalink)