11/3 Mon
IP Address
Special addresses
|
Prefix |
Suffix |
Address Type |
Purpose |
|
All 0¡¯s |
All 0¡¯s |
This computer |
Bootstrap - Real address is
not available |
|
Network # |
All 0¡¯s |
Network |
Used to refer
to a network ( Network ID ) |
|
Ex)
128.10.0.0-> cs.purdue.edu network / class B, 128.10.3.0-> faculty network /
class C |
|||
|
Network # |
All 1¡¯s |
Directed
broadcast |
Broadcast in a
determined network |
|
Ex) 128.10.3.255
-> broadcast address in faculty net. 128.10.255.255 ->
broadcast to all cs.purdue.edu subnet |
|||
|
All 1¡¯s |
All 1¡¯s |
Limited
broadcast |
Broadcast in
local net |
|
Ex)
255.255.255.255 -> broadcast local net |
|||
|
127 |
Any |
Loopback |
testing |
|
Ex) 127.0.0.1
-> localhost |
|||
11/5 Wed
InternetPhone project
2 programs
1 – Directory Server
-
Dialog based
2 – phone program
-
Includes Directory Client, Ringer Client/Server, Play Server/Voice Client
IP
Packets
Because the internet connects heterogeneous networks, a
router will copy the packets arriving in one network and copying them in
another.
To accommodate heterogeneity, an internet must define a
hardware independent packet format.
IP Packet == IP Datagram
IP packets are the basic unit of communication in the
internet
IP Packet Header
|
0 3 |
4 7 |
8
11 |
12
15 |
16
19 |
20
23 |
24
27 |
28
31 |
|
Ver |
H Len |
Service Type |
Total Length |
||||
|
ID |
Flags |
Fragment Offset |
|||||
|
Time To Live |
Type |
Header Checksum |
|||||
|
Source IP |
|||||||
|
Destination IP |
|||||||
Version : 4 bit
-
current version is 4
-
new version is 6 ( still not widely used )
Header length : 4 bit
-
it is usually 20 bytes ( this number is in words of 4 bytes
or 5 words )
-
if IP options are used, then header will be longer
Service type : 8 bit
-
priority ( usually ignored )
Total length : 16 bit
-
number of bytes in the packet including header
-
2^16 = 64KByte max
ID : 16 bit
-
monotonically increasing number different in each packet
coming from the same source – 64k identifiers ( 0 ~ 64k )
-
it will start with random number and ( id++ % MAX_LEN )
Flag : 4 bit
-
do not fragment bit ( router should not fragment packets )
-
last fragment bit ( set to 1 if the packet is the last
fragment )
Fragment offset : 12 bit
-
position of the packet in the original packet if it is
fragmented
l
Reassembly is done at destination, not in the router.
n
Reassembly is not done in router because there is no guarantee
that each packet will take same path ( some packets go through router ¡®A¡¯ and
the other go through router ¡®B¡¯ )
l
Do not fragment bit is used to find PATH MTU
11/5 Wed
IP Packet Header
|
0 3 |
4 7 |
8
11 |
12
15 |
16
19 |
20
23 |
24
27 |
28
31 |
|
Ver |
H Len |
Service Type |
Total Length |
||||
|
ID |
Flags |
Fragment Offset |
|||||
|
Time To Live |
Type |
Header Checksum |
|||||
|
Source IP |
|||||||
|
Destination IP |
|||||||
Time To Live ( TTL ) : 8 bit
-
Maximum number of seconds the packet should remain in the
internet.
-
It is decremented by 1 every second the packet stays in the
router queue
-
It is decremented by 1 every time the packet is routed by a
router
-
If the TTL field reaches 0, the packet is discarded, and
ICMP message ¡°Time expired¡± is sent to the source
-
Since the TTL field is 8 bits long, the maximum number of
seconds, the packet can be in the internet will 255 seconds.
-
The packet can be routed 255 times max
-
This prevents a packet being forwarded forever.
IP Type : 8 bit
-
It tells the protocol on top of IP that is encapsulated in
the data field : TCP/UDP/ICMP
Header checksum : 16 bit
-
Checksum of the IP header to check possible errors.
Source IP : 32 bit
-
IP address of source host
-
Initial source
Destination IP : 32 bit
-
IP address of destination host
-
Final destination
l
Source and destination do not change during the transit of
the IP packet.
l
The header may have additional information known as ¡°IP
options¡±
n
Example of IP options
n
record route
u
add the IP address of the router to the header every time
the packet is routed
n
strict routing
u
loose follow the routing path indicated in the header
l
IP options are used in Network diagnostics
IP semantics
-
IP is connectionless
n
A datagram contains the destination and the identity of
packet, the IP packet is ¡°self contained¡±, the packet contains everything it
needs to reach its destination.
n
Each IP packet ( datagram ) is handled independently
-
Routers can change at any time
-
IP datagrams can be
n
Delayed
n
Duplicated
n
Delivered out of order
n
Lost
IP is a ¡°best effort¡± delivery protocol.
That means that the network hardware and protocol will do ¡°their
best¡± to deliver packets but errors may occur.
The motivation for IP being so flexible is to accommodate
all possible networks.