2
Three Level of Address
• Host name– ratree.psu.ac.th
• Internet IP address– 192.168.100.3
- (32 bits address with “dot decimal” notation)
• Station address : Hardware address assi gned to network interface card, refer to
MAC address or Ethernet Address 48(bi t s)–00503004
3
Converting Host Name to MAC Address
cs05.cs.psu.ac.th
172.28.80.96
00:50:ba:49:9d:b9
Resolve IP address by Domain Name System(DNS)
Resolve MAC address by Address Resolution Protocol(ARP)
4
IP Address with Router
IP address associated with interface (not machine)
• Each interface has its own IP address
• Machine with more than one interface called multi-home
• Router is multi-homed machine
• Multi-homed not to be router
172.28.80.15172.28.80.16172.28.85.116172.28.85.120
172.28.85.1172.28.80.1
192.168.100.3192.168.100.4
192.168.100.1
192.168.99.39
192.168.98.11
Internet
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IP Address
Network Host
32 bits
8,16,24 bits
8 bits 8 bits 8 bits 8 bits
32 bits
172 28 80 96. . .10101100000111000101000001100000
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IP Address Class
32 bits address length, contain 2 parts
• Network identifier• Host identifier
Class A8 16 24 32
Host IDNetwork ID0
Multicast Address1110
Unused11110
Host IDNetwork ID110
Host IDNetwork ID10Class B
Class C
Class DClass E
8
IP Address Class
A 0 7 24 0.0.0.0 -127.255.255.255 224 16,677,214
B 10 14 16 128.0.0.0 -191.255.255.255 216 65,534
C 110 21 8 192.0.0.0 -223.255.255.255 28 254
D 1110 28 - 224.0.0.0-239.255.255.255
E 11110 27 - 240.0.0.0-247.255.255.255
ClassInitial bits
Bit net
Bithost range address
spacesusable
9
Special Address• Host ID 0“all s” is reserved to refer to network
number– 1921681000 15810800. . . , . . . ,18000. . .
• Host ID “ 1 ”all s is reserved to bbbbbbbbb bb bbb b osts on a specific network
– 192168100255 1581082. . . , . . 55255 18255255255. , . . .
• Address 0.0.0.0 means “defaultroute”• mmmmm 127000 “this node” (local loopb
ack). Message sent to this address will never lea ve the local host
• 255255255255Address . . . is reser ve t o broadcast to every host on the local n
etwork (limited broadcast)
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Problem with Class Assignment
• Class A takes 50 % range
• Class B takes 25 % range
• Class C take 12.5 % range
These leads to:• address wasteful
(specially in class A)• running out of IP address
Class AClass B
CD
E
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How to assigns IP Address (RFC 1466)
• Class A : no allocations will be made at this time
• Class B: allocations will be restricted. To apply:– organization presents a subnetting more
than32 subnets– organization more than 4096 hosts
• class C: divided into allocated block to distributed reginal
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Class C Assignment • Assignment is based on the subscriber ‘s 24 month
projection according to the criteria:1. Requires fewer than 256 addresses : 1 class C
network2. Requires fewer than 512 addresses : 2 contiguous
class C networks3. Requires fewer than 1024 addresses : 4 contiguous
class C networks4. Requires fewer than 2048 addresses : 8 contiguous
class C networks5. Requires fewer than 4096 addresses : 16 contiguous
class C networks6. Requires fewer than 8192 addresses : 32 contiguous
class C networks7. Requires fewer than 16384 addresses : 64 contiguous
class C networks
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Problem with Large Network
•Class B “Flat Network” more than 60,000 hosts–How to manage?–Performance?...150.0.0.1150.0.0.2 150.0.255.254
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Problem with Large Network
•Class B “subdivided network” to smaller group with router
150.0.10.1150.0.10.2
150.0.40.1150.0.40.2
150.0.200.1150.0.200.2
150.0.1.1150.0.1.2
Router
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Subnetwork Benefits
• Increase the network manager’s control the address space
• Easy to allocate the address space• Better network performance• Hide routing structure from remote routers,
thus reducing routes in their routing tables• Subdivide on IP network number is an
important initial task of network managers
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How to assign subnet• Divide host ID into 2 pieces
• Class B address such as 150.0 might use its third byte to identify subnet– subnet1 150.0.1.X X = host address
range from 1-254– subnet2 150.0.200.X
Network IDSubnet addressHost address
host ID
Choose
appropriate size
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Subnet Mask
• 32 bit number, tell router to recognize the subnet field, call subnet mask
• subnet rule: The bit covering the network and subnet part of address are set to 1
• Example class B with 24 bits mask1111 1111 1111 1111 1111
1111 0000 0000 subnet mask = 255.255.255.0
* zero bit are used to mask out the host number resulting the network address
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Subnet Mask 2552552550Subnet mask . . . for cl
m mmmmmm:• 254network has been partition to subnets
150101 15010254. . .X to . . .X• mmmmmmm mm mmmmmmm mmmm mmmm mmmmmm mmmmmmm “”
mmmmmmm15010155. . . 15010240243
mmm mmm2552552550. . .2552552550. . .1501000. . . 1501000. . .
same network address
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Subnet Mask Bits
Use contiguous subnet mask 128 64 32 16 8 4 2 1 1 0 0 0 0 0 0 0 =
128 1 1 0 0 0 0 0 0 =
192 1 1 1 0 0 0 0 0 = 224 1 1 1 1 0 0 0 0 = 240 1 1 1 1 1 0 0 0 = 248 1 1 1 1 1 1 0 0 = 252 1 1 1 1 1 1 1 0 = 254 1 1 1 1 1 1 1 1 = 255
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Subnet Class B Example• 255.255.0.0 (0000 0000 0000 0000)
0 subnet with 65534 hosts (default subnet)
• 255.255.192.0 (1100 0000 0000 0000)2 subnets with 16382 hosts
• 255.255.252.0 (1111 1100 0000 0000)62 subnets with 1022 hosts
• 255.255.255.0 (1111 1111 0000 0000)254 subnets with 254 hosts
• 255.255.255.252 (1111 1111 1111 11000)16382 subnets with 2 hosts
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Subnet Class C Example
• 255.255.255.0 ( 0000 0000)0 subnets with 254 hosts (default subnet)
• 255.255.255.192 (1100 0000)2 subnets with 62 hosts
• 255.255.255.224 (1110 0000)6 subnets with 30 hosts
• 255.255.255.240 (1111 0000)14 subnets with 14 hosts
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Subnet Interpretation
IP Address Subnet mask Interpretation158.108.2.71 255.255.255.0 host 71 on subnet
158.108.2.0150.10.25.3 255.255.255.192 host 3 on subnet
150.10.25.0130.122.34.132 255.255255.192 host 4 on
subnet 130.122.34.128200.190.155.66 255.255.255.192 host 2 on
subnet 200.190.155.6418.20.15.2 255.255.0.0 host 15.2 on subnet
18.20.0.0
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Subnet Routing
Traffic is route to a host by looking “bit wise AND” results
if dest IP addr & subnet mask = = my IP addr & subnet mask
send packet on local network { dest IP addr is on the sa me subnet}
else
send packet to router {dest IP address is on difference subnet}
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Type of Subnet
• Static subnet: all subnets in the subnetted network use the same subnet mask– pros: simply to implement, easy to maintain– cons: wasted address space (consider a
network of 4 hosts with 255.255.255.0 wastes 250 IPs)
• Variable Length Subnet : the subnets may use difference subnet masks– pros: utilize address space– cons: required well managment
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Variable Length Subnet Mask• General idea of VLSM
– A small subnet with only a few host s needs a subnet mask that accom
modate only few hosts– A subnet with many hosts need a s
ubnet mask to accomdate the larg e number of hosts
• Network Manager’s responsibility to design and appropriate VLSM