1. IP : Internet Protocols

2. Agenda IP functions IP header format IP routing Fragmentation
IPng’s overview

3. Connectionless Delivery System
Most fundamental internet service consists of a packet delivery system
Service is defined as
Unreliable
Best-effort
Connectionless

4. Purpose Of Internet Protocol
Protocol that defines the unreliable, connectionless delivery mechanism is called Internet Protocol and usually called IP
IP has 3 important definitions
Basic unit of data transfer used throughout a TCP/IP internet
IP software perform the routing function
Including a set of rule that embody the idea of unreliable packet delivery

5. IP layer
defines a single virtual network on top of different kinds of hardware platform using IP address
functions of IP
route packet
fragmentation
handle type of services
send and receive error and control message using ICMP

6. IP attributes handle data unit called IP datagrams
connectionless protocol - doesn’t promise reliable delivery
best effort delivery
packets may be lost, out out sequence, or duplicated due to various reasons

7. IP encapsulation Ethernet hdr IP header data with Ethernet frame
IP datagrams
Ethernet hdr IP header data

8. IP reframing Œ  IP will reframe the packet when A send data to B
MAC 0:0:c:6:13:4a IP
MAC 0:0:c:6:12:40
MAC dest
MAC src
type
IP source
IP dest
0:0:c:6:13:4a
0:0:e8:15:cc:c
0x800
packet to router
MAC dest
MAC src
type
IP source
IP dest
0:0:33:10:a:c
0:0:c:6:12:40
0x800
packet from router IP
MAC 0:0:e8:15:cc:c A B IP
MAC 0:0:33:10:a:c
Change MAC address, IP address be the same

9. IP datagrams 0 15 16 31 vers:4 hlen:4 TOS:8 total length:16
vers:4 hlen: TOS: total length:16
identification: flags: frag offset:13
time to live: protocol: header checksum :16
source address :32
destination address :32
options and padding :32
data : 20
bytes

10. IP header details (1) vers - version = 4
hlen - header length in 32-bit words,
with no options, hlen = 5 = 20 bytes
TOS - type of service, desired quality of services
Prec. D T R
bits if if 1
Precedence
Normal delay Low delay
Normal throughput High throughput
Normal Reliability High reliability
6-7 Reserved

11. IP header details (2)
Total length - length of datagrams (incl. header), max datagrams is 64K
identification, flags, fragmentation - use to segmentation and reassembly packet
TTL - Time to live, defining max number of routers through which the datagrams may pass (hop count)
ttl-- decrease each router it passes a router
normally set to 30
if ttl == 0 discard and send ICMP TTL exceeded to source IP (prevent looping)

12. IP header details (3)
Protocol - higher-level protocol that provides data
1 = datagrams carries an ICMP messages
6 = datagrams carries an TCP segments
17 = datagrams carries an UDP datagrams
header checksum - 16 bit one’s compliment, note that there is no data checksum
source address bit IP source address
destination address bit IP destination address
option and padding - additional info to control functions such as routing and security

13. Routing
routing is a process of choosing a path over which to send datagrams
IP routes packet by looking at the IP network number
routing components
determine what path are available
selecting the best path for a particular purpose
using those paths to reach other networks
devices which perform routing are routers (historically call IP gateways)

14. Routing Table
Every router contains a routing table of the network numbers
The table records
which connection can be used to reach a particular network
plus some indication of the performance or cost of using connection

15. Routing Table form Routing Table form
<network, gateways, others>
% netstat -rn
Destination Gateway Genmask Flags MSS Window irtt Iface
U eth0
U lo
UG e

16. How to create routing table
IP does not create routing table by itself
Normal 3 ways to create routing table
static route - by hand
% route add
dynamic routes - via routing protocol
via ICMP redirect

17. Routing Protocol
Routing protocol manages and updates routing table on each network node
often implemented in UNIX using one of the two daemons:
routed : basic routing daemon for interior routing, normally with RIP
gated : sophisticated daemon for interior and exterior routing, with additional protocol such as OSPF, BGP

18. MTU revisited for fragmentation
The upper limit number of data byte in data link frame is call MTU (Maximum Transfer Unit)
Typical MTU (bytes)
FDDI : 4325
Ethernet : 1500
802.3 : 1492
Point-to-Point : 296
If #bytes of datagrams to send>link layer’s MTU, IP breaks the datagrams up into smaller pieces (fragmentation)

19. Fragmentation
fragmentation = processed used by IP to reduced size of datagram that are too big for link connection MTU e.g. fragment 2000 bytes to Ethernet (MTU=1500)
fragments should be reassembled at the final destination (expensive process)
How ?
each fragment has its own header
each fragment carries the same 16 bit identification number
Each fragment must be aligned with an eight-octet boundary

20. Fragmentation flag Identification number
16 bits integer value used to identify all fragments
This id is not a sequence number!
flags - 3 bits control fragmentation
0= may fragment
1= don’t fragment
0= last fragment
1= more fragments
reserve,
must be 0
R DF MF
fragment offset - indicate the distance of fragment data from the start of the original datagram, measure in 8 octets unit

21. Fragmentation sample ……. 232 0 0 0..2000 ... 111 1 0 0..1479
other header ident flags offset data
original ……
20 bytes
20 bytes
Ethernet
with MTU
of 1500
identification number
Now you have reviewed the evolution leading to the modern networks. You have seen the use of a model and been introduced to the operations and functions at each layer. The remaining three chapters of this Introduction to Internetworking (I2I) module will proceed as follows:
Applications and Upper Layers - Network applications layers and how they provide application, data presentation, and session functions; also the upper layer that provides end-to end services between hosts using transport layer services.
Physical and Data Link Layers - Data transmission services provided by lower layer functions, with specific variations for LAN and WAN framing and media.
Network Layer and Path Determination - Routing using Layer3 services of the network layer, and other processes; thi is the primary domain of the router.
more fragment
last fragment
post 185*8=1480
post 0

22. Problem in fragmentation
The end node has no way of knowing how many fragments there be. It has to manage enough buffer space to handle reassembly process.
If any fragments lost, all datagram must be discarded
End node starts a timer when received the first fragment, if any fragments fails to arrive (usually 30 secs), all datagrams must be discarded
Since the IP service is connection's. No attempt is made by IP to recover these situations, though ICMP error message may be generated

23. Path MTU
Path MTU : the smallest MTU of data link between two distance hosts
Need not to be constant because routing mechanism
Avoid fragmentation by discover PATH MTU (RFC1191)
Use ICMP to determine PATH MTU

24. Avoiding fragmentation
For datagrams within the same physical network, the MTU is known. TCP/UDP then use the MTU to limit the message size pass to IP; messages will never be fragmented.
For datagrams passed to diff net, not easy to know the MTU!
standard recommends that all networks supporting TCP/IP have an MTU of at least 576 bytes bytes data+20 bytes TCP hdr + 20 bytes IP hdr with options TO GUARANTEED THAT A PACKET OF 576 BYTES OR LESS IS NEVER FRAGMENTED

25. IPng
Problem of current IP address : limitation of 32 bit address space
1990 : IETF defined a new version of IP, generally called IP Next Generation or IPng
Spring 1992 : IAB issues IPv7, proposed the OSI CLNP (connectionless Network Protocol) as the basis of IPv7. Finally rejected by IETF and working groups

26. IPV6 End 1992: 7 proposals for IPng resolution to 3 possibilities :
CNAT, IP Encaps, Nimrod, Simple CLNP, P Internet Protocol, SIP, and TP/IX
resolution to 3 possibilities :
SIP+ TP/IX => TUBA (TCP and UDP with bigger Address: RFC 1347)
TP/IX => CATNIP (Common Architecture for the Next Generation Internet Protocol :RFC1707)
SIP+IP encaps+PIP=> SIPP (Simple Internet Protocol Plus: RFC1710)
Mid 1994 : SIPP was chosen, known as IP version 6 (IPv6)

27. IPv6 Header destination address :128 source address :128 0 15 16 31
vers: flow lable:28
payload length: next hdr:8 hop limit:8
destination address :128
source address :128 40
bytes
40 bytes fixed length header, no checksum, options are
replace by additional extension header

28. IPV6 address representation
16 bits eight hexadecimal value e.g.
4210:30:127F:9111:7801:DA0A:3232:44
5510:0:0:0:0:0:0:44 or 5510::44
Address with mixed environment of v4 and v6
x:x:x:x:x:x:d.d.d.d
e.g. 0:0:0:0:0:

29. IPV6 key advantages
16 bytes fix length IP address support ~1000 million networks
IPv4 compatibility
self-configuration of workstations
support mobile workstations
improved security features