Interconnection
Interconnection Devices
Devices
Extended
LAN = Broadcast
domain
H
H
B
H
H
Router
Router
H
H
LAN = MAC domain
Application
Application
Gateway
Transport
Transport
Network
Router
Network
Data Link
Bridge/Switch
Data Link
Physical
Repeater
Physical
 SNU INC Lab
1
Interconnection
Interconnection Devices
Devices
ØØ Repeater
Repeater
§§ Physical
Physicallayer
layerdevice
devicethat
thatrestores
restoresand
andrelays
relayssignals
signalssignals
signals
ØØ Limitation
Limitationof
ofrepeaters
repeaters
§§ Collision
Collisiondomain
domain
§§ Physical
Physicallimitations
limitations
ØØ Hub
Hub
•• Ethernet
Ethernet––2500
2500meter
metermax.
max.distance
distance
§§ Multiport
Multiportrepeater
repeater++Fault
Faultdetection
detection&&recovery
recovery
ØØ Bridge
Bridge
§§
§§
§§
§§
Data
Datalink
linklayer
layerdevice
device
Store
Storeand
andforward:
forward:forwards
forwardsaccording
accordingto
toMAC
MAC
Extended
ExtendedLAN
LAN
Propagate
PropagateMAC
MACmulticast
multicastframe
frame
 SNU INC Lab
2
Quick
Quick Notice
Notice
Ø
Ø Office
OfficeHours
Hours
§§ Tue
Tue&&Thur
Thur9:30~10:30,
9:30~10:30,13:00
13:00~~16:00
16:00
Ø
Ø Class
Classon
onSep.
Sep. 20
20
§§ Just
추석
Justafter
afterthe
the추석
 SNU INC Lab
3
Interconnection
Interconnection Devices
Devices
Ø
Ø Router
Router
§§ Network
Networklayer
layerdevice
device
§§ Does
Doesnot
notpropagate
propagateMAC
MACmulticast
multicast
Ø
Ø Switch
Switch(layer
(layer 2)
2)
Ø
Ø
Ø
Ø
§§ Multiport
Multiportbridge
bridgewith
withparallel
parallelpaths
paths
Layer
Layer NNswitch
switch
Gateway
Gateway
§§ Transport
Transport&&upper
upperlayer
layerdevices
devices
 SNU INC Lab
4
Network
Network Layer
Layer
Ø
Functions
§
§
Construction of a logical network connecting multiple physical
networks
• internetwork, internet
End-to-end packet delivery
(internetwork, internet)
Logical Network
Network
Physical Network
Router (Gateway)
- Routing
-Arbitrate difference between
two physical networks
 SNU INC Lab
5
Internetworking
Internetworking with
with IP
IP
Ethernet
Ethernet
Y
X
Point-topoint
A
Z
B
FDDI
TCP
TCP
IP
ETH
IP
ETH
 SNU INC Lab
IP
FDDI
FDDI
IP
P2P
P2P
IP
ETH
ETH
6
IP
IP Packet
Packet Delivery
Delivery Model
Model
Ø
Ø Datagram
Datagram
§§ No
Noconnection
connectionsetup
setup
Ø
Ø Best-effort
Best-effort
§§
§§
§§
§§
§§
Lost
Lostpackets
packets
Out-of-order
Out-of-orderdelivery
delivery
Packet
Packetduplication
duplication
Delayed
Delayeddelivery
delivery
Higher
Higherlayers
layersmay
mayprovide
providereliable
reliableservice
service
Ø
Ø IP
IPcan
canaccommodate
accommodate(almost)
(almost) any
anyhardware
hardware
technologies
technologies
 SNU INC Lab
7
IP
IP Address
Address
Ø
Ø Each
EachInternet
Internet host
hosthas
hasaauniversally
universallyunique
uniqueIP
IP
address
address
Ø
Ø Format
Format
§§ 44bytes
bytes
§§ Hierarchical
Hierarchical--Class
Class
Net ID
Host ID
InterNIC (or local authority or ISP) assigns a Net ID to an AS (or large
customer)
AS(Autonomous System) assigns Host ID for each host
 SNU INC Lab
8
IP
IP Address
Address Notations
Notations
Ø
Ø Binary
Binary
-- 11000000
11000000 00000101
0000010100110000
0011000000000011
00000011
Ø
Ø Dotted
Dotteddecimal
decimal
-- 192.5.48.3
192.5.48.3
 SNU INC Lab
9
IP
IP Address
Address Classes
Classes
0
Net ID
10
Net ID
1 10
Host ID
Net ID
1 11 0
 SNU INC Lab
Class A
Host ID
Multicast Address
Class
Range (First Byte)
A
B
C
D
E
0 - 127
128 - 191
192 - 223
224 - 239
240 - 255
Host ID
Class B
Class C
Class D
10
Special IP Addresses
Ø All-0 host suffix
§
Network address
Ø All-0s
§
This host
Ø All-1 host suffix
§
§
All hosts in the specified net
Directed broadcast
Ø All-1s
§
§
All hosts on this net
Limited broadcast
Ø 127.*.*.*
§
Loopback through IP layer
 SNU INC Lab
11
IP
IP Addressing
Addressing
Ø
Ø All
Allhosts
hostson
onaasame
samephysical
physical network
networkhave
havethe
the
same
samenetwork
networkprefix
prefix
128.211
128.10
128.211.6.5
128.10.0.1
128.10.0.2
10
10.0.0.37
 SNU INC Lab
192.5.48.3
192.5.48
10.0.0.49
12
Multi-homing
Multi-homing
Ø Host may connect more than one networks
§
§
Each interface has its own IP address
An IP address is assigned to an interface not to a host
Ethernet
Token Ring
223.240.129
131.108
131.108.99.5
223.240.129.2
223.240.129.17
WAN 78
78.0.0.17
 SNU INC Lab
13
IP Routing
Ø
Direct and Indirect delivery
§Direct – Destination is in the same physical network
§Indirect – Destination is on other physical network
Case 1: Host a --> Host b
Host a knows that host b is in the same physical network
How?
Case 2: Host a --> Host c
Host a relay datagram to router A or B
a
c
B
E
C
b
A
 SNU INC Lab
F
D
d
14
Forwarding
Forwarding Table
Table
Ø Format
§
§
<Destination ID, next hop>
Destination ID is the network prefix of an IP address
Ø Hop by hop forwarding
§
A forwarding table indicates the next hop router (or direct
delivery) toward the final destination
Forwarding table
at node a
 SNU INC Lab
Destination ID
Net.1
Net 2
Net 3
Net 4
Net 5
Next hop
Direct delivery
Router B
Router A
Router B
Router A
15
Forwarding
Forwarding Table
Table Reduction
Reduction
Ø
Ø
Ø
Ø
Network
Networkbased
basedrouting
routing
Default
Default route
route
Destination ID
Net.1
Net 2
Net 4
Deafult
Next hop
Direct delivery
Router B
Router B
Router A
Ø
Ø Search
Searchsequence
sequenceis
isimportant
important
§§ From
Fromspecific
specificto
togeneral
general
 SNU INC Lab
16
Example
Example
10.0.0.1
20.0.0.0
a
c
B
10.0.0.0
10.0.0.5
b
A
10.0.0.7
30.0.0.4
E
40.0.0.0
40.0.0.0
C
30.0.0.0
40.0.0.5
F
D
50.0.0.0
50.0.0.0
d
50.0.0.1
A
10.0.0.4
20.0.0.3
B
20.0.0.1
30.0.0.1
C
30.0.0.6
50.0.0.2
D
 SNU INC Lab
17
Physical/Logical Network Interaction
Host a (10.0.0.1) sends a datagram to Host c (40.0.0.5)
Assume that it takes the following path
20.0.0.3
= 389
a
10.0.0.0
10.0.0.1
= 077
10.0.0.4
= 104
B
20.0.0.5
= 300
20.0.0.0
E
40.0.0.0
40.0.0.1
= 548
c
40.0.0.5
= 731
End-to-end delivery over a logical network is realized by
- Repetitive hardware routing within a series of physical networks
- Network layer routing at intermediate routers
 SNU INC Lab
18
ARP
ARP (Address
(Address Resolution
Resolution protocol)
protocol)
Ø
Ø Problem
Problem
§§ Each
Eachhost
hosthas
hastwo
twodifferent
differentaddresses
addresses
§§ Physical
Physicaladdress
address(Hardware
(Hardwareaddress)
address)
§§ Logical
Logicaladdress
address(Protocol
(Protocoladdress,
address,IP
IPaddress)
address)
D
B
A
C
 SNU INC Lab
F
Assumption: Every host knows its own logical &
Physical addresses
Suppose A wants to send a packet to C
E
19
ARP
ARP –– Basic
Basic
Ø
Ø Use
Useaatable
tablethat
that maps
mapsIP
IPaddress
address––MAC
MACaddress
address
pairs
pairs
IP address
MAC address
197.15.3.1
197.15.3.2
197.15.3.3
197.15.3.4
197.15.3.5
0A:4B:00:00:07:08
0B:4B:00:00:07:00
0A:5B:00:01:01:03
04:06:07:08:09:10
06:07:09:08:03:01
Ø
Ø How
How and
andwho
whomanages
managesthe
thetable
table??
 SNU INC Lab
20
ARP
ARP –– Two
Two Methods
Methods
Ø
Ø Two
Twotypes
types of
ofnetwork
network
§§ Broadcast
Broadcastnetwork:
network:LANs
LANs(Ethernert,
(Ethernert,Token
Tokenring,
ring,…)
…)
§§ NBMA
NBMA(Non-Broadcast
(Non-BroadcastMultiple
MultipleAccess)
Access)
•• Example:
Example:ATM,
ATM,X.25
X.25
Ø
Ø Two
TwoARP
ARPapproaches
approaches
§§ Distributed
Distributed
••
••
Each
Eachhost
hostbuilds
buildsthe
themapping
mappingtable
table
Get
Getmapping
mappinginformation
informationasking
askingto
tothe
thetarget
target
••
••
Only
Onlyspecialized
specializedARP
ARPserver
serverhave
havethe
thetable
table
Usually,
Usually,each
eachhost
hostperiodically
periodicallyreports
reportsits
itsown
ownmapping
mapping
information
to
the
servers
information to the servers
§§ Centralized
Centralized
 SNU INC Lab
21
ARP - Distributed
Broadcast
Network
A
B
C
D
E
Suppose host A wants to send a packet to host C
First, host A looks up its ARP cache for C’s mapping information
If the inf. does not exist, Host A broadcasts request packet
==> Everyone receives the request
Host C sends back a response message
How do you design a protocol ??
 SNU INC Lab
22
ARP
ARP Packet
Packet Format
Format
Ø
Ø IP-Ethernet
IP-Ethernet
HW Type
HLEN
PLEN
Protocol Type
Operation
Sender HA (Octets 0-3)
Sender HA (octets 4,5)
Sender IP (Octet 0,1)
Sender IP (octets 2,3)
Target HA (Octet 0,1)
Target HA (Octets 2-5)
Target IP (Octets 0-3)
 SNU INC Lab
23
ARP
ARP Processing
Processing
Ø
Ø
ARP responses are cached
Entry replaced (or purged) when
§
Cache table overflow
• Policy?
§
After timeout
• E.G. 20 min
Ø
How do you reduce ARP traffic ??
§
§
Ø
Proxy ARP
§
Ø
Cache inf. In the request
Cache inf. In the response
A server (usually a router) may act as a proxy for many IP
address
Gratuitous ARP
 SNU INC Lab
24
Reverse
Reverse ARP
ARP (RARP)
(RARP)
Ø
Ø AAhost
host may
maynot
not know
knowits
itsIP
IPaddress
address
§§ Knows
Knowsits
itshardware
hardwareaddress
address
Ø
Ø Problem
Problem
§§ What
Whatisisthe
theIP
IPaddress
addressof
ofaagiven
givenh/w
h/waddress?
address?
§§ RARP
RARPserver
server
Ø
Ø BOOTP
BOOTP
§§ To
Tolease
leasean
anIP
IPaddress
addresstemporarily
temporarily
Ø
Ø DHCP(Dynamic
DHCP(DynamicHost
HostConfiguration
ConfigurationProtocol)
Protocol)
§§ Advanced
AdvancedBOOTP
BOOTP
 SNU INC Lab
25
DHCP
Ø
To join the Internet, a host needs
§
§
§
Ø
Unique IP address
Forwarding table – Default router
DNS server
DHCP
§
§
A protocol to auto-configure IP address, default router & DNS
server
DHCP server has information
• A pool of available IP addresses
• Default routes & DNS server inf.
DHCPDISCOVER
Reply
 SNU INC Lab
26
DHCP
DHCP Packet
Packet Format
Format
Operation
Operation
HT
ype
HT
ype
HLen
HLen
Hops
Hops
Xid
Xid
Secs
Secs
Flags
Flags
ciaddr
ciaddr
yiaddr
yiaddr
siaddr
siaddr
giaddr
giaddr
chaddr
chaddr(16
(16bytes)
bytes)
sname
sname(64
(64bytes)
bytes)
file
file(128
(128bytes)
bytes)
 SNU INC Lab
options
options
27
DHCP
DHCP Relay
Relay
Ø
Ø DHCP
DHCPserver
server for
for each
eachnetwork
network
§§ Management
Managementoverhead
overhead
Ø
Ø Relay
Relay
Unicast to server
Broadcast
DHCP
relay
Other networks
DHCP
server
Host
 SNU INC Lab
28
DHCP
DHCP Ref.
Ref.
nd
Ø
Ø R.
R. Droms,
Droms,“The
“TheDHCP
DHCPHandbook”,
Handbook”, 22ndEd.,
Ed.,
SAMS
SAMS
Ø
Ø RFC
RFC2131,
2131, http://www.ietf.org/rfc/rfc2131.txt
http://www.ietf.org/rfc/rfc2131.txt
 SNU INC Lab
29
IP
IP Datagram
Datagram Format
Format
VERS HLEN Service Type
ID
TTL
Total Length
Flags
Protocol
Fragment Offset
Header Checksum
SA
DA
IP Options (If Any)
Padding
Data
* IETF has finished IPv6 called IPng
 SNU INC Lab
30
IP
IP Datagram
Datagram Format
Format
Ø
Version
§
§
Ø
Type of service
§
§
§
Ø
Ø
Ø
Currently 4
New version = 6
Reliability
Delay
Throughput
Total length
§
Header + data in bytes (Max = 64 KB)
§
§
Uniquely identify a datagram during its lifetime
For fragment reassembly
ID
Flags
§
§
M (More flag)
Do-not-fragment
 SNU INC Lab
31
IP
IP Datagram
Datagram Format
Format
Ø TTL (Time To Live)
§
In hop count
Ø Protocol
§
Next layer protocol to receive the data
 SNU INC Lab
Decimal
Protocol
0
1
2
4
5
8
9
17
Reserved
ICMP
IGMP
ST (Stream protocol)
TCP
EGP
IGP
UDP
32
IP
IP Datagram
Datagram Format
Format
Ø
Ø Header
Header checksum
checksum
§§ 1’s
1’scomplement
complementsum
sumof
ofall
all16-bit
16-bitwords
wordsininthe
theheader
header
Ø
Ø Source
Source&&destination
destinationaddresses
addresses
§§ Original
Originalsource
source&&destination
destination
§§ Invariable
Invariable
Ø
Ø Options
Options
§§
§§
§§
§§
Security
Security
Source
Sourceroute
route
Record
Recordroute
route
Stream
StreamID
IDfor
forreserved
reservedresource
resource
•• For
Forvoice
voice
§§ Timestamp
Timestamp
 SNU INC Lab
33
IP Options Coding
Ø TLV Format
Type
1B
Flag Copy
1b
Length
1B
Class
2b
Value
nB
Number
5b
Flag Copy
0: Copy the option only into the first fragment
1: Copy into all fragments
Class
0: User or control
1: Reserved
2: Diagnostics
3: Reserved
 SNU INC Lab
34
IP
IP Options
Options
Ø
Ø ..
Class
Number Length
Description
0
0
0
0
0
0
0
2
0
1
2
3
7
8
9
4
End of Options
No Op
Security
Loose Source Routing
Record Route
Stream ID (Obsolete)
Strict Source Routing
Internet Timestamp
 SNU INC Lab
0
0
11
Var
Var
4
Var
Var
35
Fragmentation
Fragmentation &
& Reassembly
Reassembly
Ø MTU (Maximum Transfer Unit)
§
§
Maximum frame size that a physical network can
transmit
Different physical networks have different MTUs
• Ethernet - 1500 Byte
• FDDI - 4500 Byte, TR - 8000 Byte
Ethernet
Router
Router
8000 Byte
 SNU INC Lab
36
Fragmentation
Fragmentation &
& Reassembly
Reassembly
Ø Fragmentation
§
§
Partitioning of a datagram into multiple smaller fragments
Sizes <= MTU of next physical network
Ø Reassembly
§
§
Concatenation of fragments into the original datagram
Protocol principle
 SNU INC Lab
37
Fragmentation
Fragmentation &
& Reassembly
Reassembly
MTU = 2000
MTU = 820
MTU = 2000
Original =
2000 Byte
Fragments =
820 Byte
Fragments = 400 Byte
 SNU INC Lab
Information for reassembly
ID
Offset
Total length
Flag
38