l9cn : network layer: internet protocol
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Internet Protocol
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.20.1
2020--11 INTERNETWORKINGINTERNETWORKING
connectingconnecting networksnetworks togethertogether toto makemake ananinternetworkinternetwork oror anan internetinternet..
Topics discussed in this section:Topics discussed in this section:
Internet as a Datagram Network
Internet as a Connectionless Network
20.2
. n s e ween wo os s
20.3
. e wor ayer n an n erne wor
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. e wor ayer a e source, rou er, an es na on
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. e wor ayer a e source, rou er, an es na on con nue
20.6
Note
w c ng a e ne wor ayer n eInternet uses the datagram approach to
pac e sw c ng.
20.7
Note
ommun ca on a e ne wor ayer nthe Internet is connectionless.
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Two Key Network-Layer Functions
analo :
packets from routersinput to appropriate
routing: process oflannin tri from
router output
source to dest
forwardin : rocess ofroute taken by packetsfrom source to dest.
getting through singleinterchange
routing algorithms
20.9
Interplay between routing and forwarding
routing algorithm
local forwarding table
header
value
output
link0100 3010101111001
221
10111
value in arrivingpackets header
23
20.10
Router Architecture Overview
Two key router functions: run routing algorithms/protocol (RIP, OSPF, BGP)
forwardingdatagrams from incoming to outgoing link
20.11
Physical layer:bit-level reception
given datagram dest., lookup output port
using forwarding table in input portmemor
a a n ayer:e.g., Ethernet
goal: complete input port processing at line
speed queuing: if datagrams arrive faster than
forwarding rate into switch fabric
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Three types of switching fabrics
20.13
Switching Via Memory
First generation routers:
traditional computers with switching under direct
control of CPUpacket copied to systems memory
per datagram)
Input OutputMemory
Port Port
System Bus
20.14
Switc ing Via a Bus
datagram from input port memoryto output port memory via a sharedbus
us con en on: sw c ng speelimited by bus bandwidth
32 Gb s bus Cisco 5600: sufficientspeed for access and enterprise
routers
20.15
Switchin Via An Interconnection Network
overcome bus bandwidth limitations
Ban an networks other interconnection nets initialldeveloped to connect processors in multiprocessor
advanced design: fragmenting datagram into fixed, .
Cisco 12000: switches 60 Gbps through theinterconnection network
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Output Ports
Bufferingrequired when datagrams arrive from fabric
Scheduling disciplinechooses among queueddata rams for transmission
20.17
Output port queueing
line speed
queueing (delay) and loss due to output port bufferoverflow!
20.18
How much buffering?
buffering equal to typical RTT (say 250
e.g., C = 10 Gps link: 2.5 Gbit buffer
ecen recommen a on: w ows,buffering equal to RTT C.
N
20.19
Input Port Queuing
Fabric slower than input ports combined -> queueingmay occur at input queues
Head-of-the-Line (HOL) blocking: queued datagram at
front of queue prevents others in queue from moving
queueing delay and loss due to input buffer overflow!
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2020--22 IPvIPv44
mechanismmechanism usedused byby thethe TCP/IPTCP/IP protocolsprotocols..
Topics discussed in this section:Topics discussed in this section:
Fragmentation
Checksum
Options
20.21
The Internet Network layer
Host, router network layer functions:
Routing protocolsIP protocol
Transport layer: TCP, UDP
path selection
RIP, OSPF, BGP
datagram formatpacket handling conventions
Networklayer
orwar ngtable
ICMP protocol
error reporting
router signaling
Link layer
physical layer
20.22
. os on o v n pro oco su e
20.23
. v a agram orma
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IP datagram format
ver length
32 bitspro oco vers on
number
header length(bytes)
total datagramlength (bytes)
head.len
type ofservice
16-bit identifier
headerchecksum
time tolive
max numberremaining hops
fragmentation/reassembly
type of dataflgs
fragmentoffset
upperlayer
32 bit source IP address(decremented at
each router)
u er la er rotocol32 bit destination IP address
data(variable length,
to deliver payload to Options (if any) E.g. timestamp,
record routetaken, specifyhow much overhead
or UDP segment)
to visit.
20 bytes of TCP
20 bytes of IP
= 40 bytes + app
layer overhead
20.25
. erv ce ype or eren a e serv ces
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Note
e prece ence su e was par oversion 4, but never used.
20.27
Table 20.1 Types of service
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Table 20.2 Default types of service
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Note
e o a eng e e nes e o alength of the datagram including the
ea er.
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. ncapsu a on o a sma a agram n an erne rame
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. ro oco e an encapsu a e a a
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Table 20.4 Protocol values
20.33
Example 20.1
An IPv4 packet has arrived with the first 8 bits as
shown:
01000010The receiver discards the packet. Why?
Solution
There is an error in this acket. The 4 leftmost bits
(0100) show the version, which is correct. The next 4
bits (0010) show an invalid header length (2 4 = 8).
The minimum number of bytes in the header must be20. The packet has been corrupted in transmission.
20.34
Example 20.3
In an IPv4 packet, the value of HLEN is 5, and the
value of the total len th field is 0x0028. How man
bytes of data are being carried by this packet?
Solution
The HLEN value is 5 which means the total number of
bytes in the header is 5 4, or 20 bytes (no options).The total length is 40 bytes, which means the packet is
carrying20bytes of data (4020).
20.35
. ax mum rans er un
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. s or some ne wor s
20.37
IP Fragmentation & Reassembly
network links have MTU(max.transfer size) - largestpossible link-level frame.
different link types, differentMTUs
fragmentation:
in: one large datagram
arge a agram v e(fragmented) within net
one datagram becomesseveral data rams
reassembled only at finaldestination
IP header bits used to
reassembly
identify, order relatedfragments
20.38
. ags use n ragmen a on
20.39
IP Fragmentation and Reassembly
ID=
offsetfragflaglength=
One large datagram becomes
several smaller datagrams
xamp e
4000 byte datagram
MTU = 1500 bytes
ID=x
offset
=0
fragflag
=1
length=1500
ID
=xoffset=185
fragflag=1
length
=1500
data field
offset =
ID
=xoffset=370
fragflag=0
length
=1040
1480/8
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. ragmen a on examp e
20.41
Figure 20.12 Detailed fragmentation example
20.42
Reassembly
When the fragments arrive what strategy should be
used to reassemble them? the ma be out of order
Solution
1. The fist fra ment has an offset field value of zero.2. Divide the length of the first fragment by 8. The
second fragment has an offset value equal to that result.
. .
The third fragment has an offset value equal to that result.
4. Continue the process. The last fragment has a more bit value
of 0.
20.43
. axonomy o op ons n v
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2020--33 IPvIPv66
TheThe networknetwork layerlayer protocolprotocol inin thethe TCP/IPTCP/IP protocolprotocol
suitesuite isis currentlycurrently IPvIPv44.. AlthoughAlthough IPvIPv44 isis wellwell
designed,designed, datadata communicationcommunication hashas evolvedevolved sincesince thethe
..
deficienciesdeficiencies thatthat makemake itit unsuitableunsuitable forfor thethe fastfast--
rowinrowin InternetInternet..
Topics discussed in this section:Topics discussed in this section:
AdvantagesPacket Format
20.45
Initial motivation: 32-bit address space
soon to be completely allocated.Additional motivation:
header format helps speedprocessing/forwarding
header changes to facilitate QoS
IPv6 data ram format:
fixed-length 40 byte header
20.46
IPv6 Header (Cont)
Priority: identify priority among datagrams in flow .
(concept offlow not well defined).
Next header:identify upper layer protocol for data
20.47
Advantages of IPv6
1. Better address space
2. Better header format
3. New options
4. Allowance of extension
5. Support for resource allocation
6. Support for more security20.48
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. v a agram ea er an pay oa
20.49
Figure 20.16 Format of an IPv6 datagram
20.50
Other Changes from IPv4
processing time at each hop
, ,indicated by Next Header field
ICMPv6:new version of ICMP
additional message types, e.g. Packet TooBig
multicast group management functions
20.51
Table 20.6 Next header codes for IPv6
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Table 20.7 Priorities for congestion-controlled traffic
20.53
. r or es or nonconges on-con ro e ra c
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Table 20.9 Comparison between IPv4 and IPv6 packet headers
20.55
. x ens on ea er ypes
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Table 20.10 Comparison between IPv4 options and IPv6 extension headers
20.57
2020--44 TRANSITION FROM IPvTRANSITION FROM IPv44 TO IPvTO IPv66
BecauseBecause of of thethe hugehuge numbernumber of of systemssystems onon thethe
n erne ,n erne , e e rans onrans on roro vv oo vv cannocanno
happenhappen suddenlysuddenly.. ItIt takestakes aa considerableconsiderable amountamount ofof
fromfrom IPvIPv44 toto IPvIPv66.. TheThe transitiontransition mustmust bebe smoothsmooth toto
preventprevent anyany problemsproblems betweenbetween IPvIPv44 andand IPvIPv66
systemssystems..
Dual Stack
Tunnelin
Header Translation
20.58
Transition From IPv4 To IPv6
simultaneous
How will the network operate with mixed IPv4
Tunneling:IPv6 carried as payload in IPv4
20.59
. ree rans on s ra eg es
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. ua s ac
20.61
. unne ng s ra egy
20.62
Tunneling
A B E F
IPv6 IPv6 IPv6 IPv6
tunnelLogical view:
Physical view:
A B E FC D
IPv6 IPv6 IPv6 IPv6IPv4 IPv4
Flow: XSrc: ADest: F
Flow: XSrc: ADest: F
Src:BDest: E
Src:BDest: E
data data
Flow: XSrc: ADest: F
data
Flow: XSrc: ADest: F
data
A-to-B: E-to-F:v IPv6- -
IPv6 insideIPv4
- -IPv6 inside
IPv4
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. ea er rans a on s ra egy
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Table 20.11 Header translation
20.65