Transcript Efficient IP Addressing

Efficient IP Addressing
Subnetting
1
Review: IP Addressing
• Suppose hosts had arbitrary addresses
– Then every router would need a lot of information
– …to know how to direct packets toward the host
1.2.3.4
5.6.7.8
host
host
2.4.6.8
...
1.2.3.5
host
host
5.6.7.9
host
2.4.6.9
...
host
LAN 2
LAN 1
router
WAN
router
WAN
router
1.2.3.4
1.2.3.5
forwarding table
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Review: IP Addressing scalability
• Number related hosts from a common subnet
– 1.2.3.0/24 on the left LAN
– 5.6.7.0/24 on the right LAN
1.2.3.4
1.2.3.7
host
host
1.2.3.156
...
5.6.7.8
host
host
5.6.7.9
host
...
host
LAN 2
LAN 1
router
1.2.3.0/24
5.6.7.0/24
forwarding table
3
5.6.7.212
WAN
router
WAN
router
Review: Scalability- Adding new hosts
• No need to update the routers
– E.g., adding a new host 5.6.7.213 on the right
– Doesn’t require adding a new forwarding entry
1.2.3.4
1.2.3.7
host
host
1.2.3.156
...
5.6.7.8
host
host
5.6.7.9
host
5.6.7.212
...
host
LAN 2
LAN 1
router
WAN
router
WAN
router
host
5.6.7.213
1.2.3.0/24
5.6.7.0/24
forwarding table
4
Some Questions: IP Addressing
• How are IP addresses managed
– Given out
• Single point
– Hierarchical
– Documentation
• Record of what is given out and to whom
– Accounting
• What remains?
5
Giving out: Obtaining a Block of
Addresses
• The Internet Assigned Numbers Authority (IANA) is responsible for the
global coordination of IP addressing, and other Internet protocol resources
– Internet Corporation for Assigned Names and Numbers (ICANN)
• Allocates large address blocks to Regional Internet Registries
– Regional Internet Registries (RIRs)
• Allocates address blocks within their regions
• Allocated to Internet Service Providers and large institutions
– Internet Service Providers (ISPs)
• Allocate address blocks to their customers
• Who may, in turn, allocate to their customers…
• Prefix: assigned to an institution
– Addresses: assigned by the institution to their nodes
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Regional Internet Registries
• Five RIRs to cater to five large global regions
• African Network Information Centre (AfriNIC) for Africa
• American Registry for Internet Numbers (ARIN) for the
United States, Canada, and several parts of the
Caribbean region.
• Asia-Pacific Network Information Centre (APNIC) for
Asia, Australia, and neighboring countries
• Latin America and Caribbean Network Information
Centre (LACNIC) for Latin America and parts of the
Caribbean region
• RIPE NCC (RIPE NCC) for Europe, the Middle East, and
Central Asia
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Record: Figuring Out Who Owns an
Address
• Address registries
– Public record of address allocations
– Internet Service Providers (ISPs) should update
when giving addresses to customers
– However, records are notoriously out-of-date
• Ways to query
8
– http://www.db.ripe.net/whois to find RIPE NCC
database for IP addresses
– http://www.geektools.com/whois.php
–…
Are 32-bit Addresses Enough?
• Not all that many unique addresses
– 232 = 4,294,967,296 (just over four billion)
– Plus, some are reserved for special purposes
– And, addresses are allocated in larger blocks
• And, many devices need IP addresses
– Computers, PDAs, routers, tanks, toasters, …
• Long-term solution: a larger address space
– IPv6 has 128-bit addresses (2128 = 3.403 × 1038)
• Short-term solutions: limping along with IPv4
– Private addresses
– Network address translation (NAT)
– Dynamically-assigned addresses (DHCP)
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Hard Policy Questions
• How much address space per geographic region?
– Equal amount per country?
– Proportional to the population?
– What about addresses already allocated?
• Address space portability?
– Keep your address block when you change providers?
• Keeping the address registries up to date?
– What about mergers and acquisitions?
– Delegation of address blocks to customers?
• As a result, the registries are horribly out of date
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What the IP Address Meltdown
Means For You
Article in PC world: posted on Dec 1, 2010 5:39 pm: Brief
synopsis
• The world is running out of IPv4 Internet addresses, without
which the Internet can't function in its existing form.
• This has been known for some time, of course, but the
situation has become a little more urgent with the news that
in October and November, nearly all of the remaining blocks
of addresses were assigned to various Regional Internet
Registries (RIR) around the world…….
• Remaining five blocks of IP addresses given out by beginning
of 2011 to the five RIRs…..
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Objectives
• Economising IP address use:
• To subnet an IP Address from given network
requirements
– Why subnet
– Hierarchy in subnetted addresses
– How to subnet
•
•
•
•
•
•
Identify network class
Identify network requirements
Calculate sub-network addresses
Calculate available host addresses
Calculate new subnet mask
Assign new addresses
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Advantages of Subnetting
• With subnetting, IP addresses use a 3-layer
hierarchy:
» Network
» Subnet
» Host
• Improves efficiency of IP addresses by not
consuming an entire address space for each
physical network.
• Reduces router complexity. Since external
routers do not know about subnetting, the
complexity of routing tables at external
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Subnetting
• Problem: Organizations have
multiple networks which are
independently managed
– Solution 1: Allocate one or
more addresses for each
network
• Difficult to manage
• From the outside of the
organization, each
network must be
addressable.
– Solution 2: Add another
level of hierarchy to the IP
addressing structure
University Network
Engineering
School
Medical
School
Library
Subnetting
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Two-level hierarchy
• The network prefix identifies a network and the host number
identifies a specific host (actually, interface on the network).
network prefix
host number
• How do we know how long the network prefix is?
– The network prefix is implicitly defined using class-based
addressing
– The network prefix is indicated by a subnet mask or
netmask
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Subnetting- Three level Hierarchy
• Split the host number portion of an IP address into a subnet number
and a (smaller) host number.
• Result is a 3-layer hierarchy
network prefix
network prefix
• Then:
host number
subnet number
host number
extended network prefix
• Subnets can be freely assigned within the organization
• Internally, subnets are treated as separate networks
• Subnet structure is not visible outside the organization
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Typical Addressing Plan for an Organization that uses
subnetting
• Each layer-2 network (Ethernet segment, FDDI
segment) is allocated a subnet address.
128.143.71.0 / 24
128.143.0.0/16
128.143.7.0 / 24
128.143.16.0 / 24
128.143.8.0 / 24
128.143.17.0 / 24
128.143.22.0 / 24
128.143.136.0 / 24
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Advantages of Subnetting
• With subnetting, IP addresses use a 3-layer
hierarchy:
»Network
»Subnet
»Host
• Improves efficiency of IP addresses by not consuming
an entire address space for each physical network.
• Note: Length of the subnet mask need not be
identical at all subnetworks.
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Task: Create subnetwork addresses
Create subnetwork addresses for 20 different network
addresses, using IP address 201.222.5.0
NETWORK 201.222.5.0
201.222.5.11
201.222.5.18
201.222.5.10
201.222.5.22
sales
201.222.5.12
E0
201.222.5.8
201.222.5.9
Admin
Subnetwork
Subnetwork
Router
201.222.5.16
E1
201.222.5.17
201.222.5.20
201.222.5.13
201.222.5.14
Routing Table
E0
201.222.5.8
201.222.5.16 E1
201.222.5.24 E2
201.222.5.32 E3
201.222.5.19
201.222.5.21
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STEP 1: Convert the decimal dotted notation
Convert the decimal dotted notation address
201.222.5.0 to binary:
11001001.11011110.00000101.00000000
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Step 2: Class of the IP Address
Determine the Class of the IP Address
201.222.5.0:
CLASS C
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Step 3. Find Network portion and Host portion
Based on the Class, determine what part of the IP
address is the network portion and what part of the
address is the host portion:
201.222.5.0
11001001.11011110.00000101.00000000
Network .Network .Network .Host
201.
222.
5.
0
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Step 4: How many bits to borrow
Determine how many bits you need to borrow
from the last octet (host portion) of the IP
Address to give you the needed 20 subnets:
2 to the power of 2 = 4 subnets (less 2)
2 to the power of 3 = 8 subnets (less 2)
2 to the power of 4 = 16 subnets (less 2)
2 to the power of 5 = 32 subnets (less 2)
2 to the power of 6 - 64 subnets (less 2)
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Step 5: Determine how many hosts can you have
on each of those subnets
Since you borrowed five bits from the host for
subnets, determine how many hosts can you
have on each of those subnets?
11001001.11011110.00000101.00000000
Remaining bits = Number of
hosts
2 to the power of 3 = 8 hosts (less 2) giving
you 6 hosts per subnet.
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Step 6: Determine the Binary Subnetworks Field
Numbers
Determine the Subnetworks’ Numbers from the borrowed 5
bits: 32 possible combinations
Subnet #
1
2
3
4
5
6
7
8
9
10
11
12
13
..
32
Binary Subnetwork
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
……..
11111
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Step 7: Determine the Range of Binary Host
Field Numbers for Each Subnetwork:
Determine the Range of Binary Host Field Numbers for Each Subnetwork:
3 bits: 8 possible hosts on each subnet
Subnet #
1
2
3
4
5
6
7
8
9
Binary Subnetwork
00000
00001
00010
00011
00100
00101
00110
00111
01000
Range of Host #’s
12
..
32
01100
……..
11111
000 - 111
-----------
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
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Step 8: Determine Decimal Host Numbers for Each
Subnetwork
Subnet #
1
2
3
4
5
6
7
8
9
10
11
12
13
..
32
Binary Subnetwork
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
……..
11111
Range of Host #’s
Decimal Host Numbers
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
000 - 111
-----------
.8 - .15
.16 - .23
.24 - .31
.32 - .39
.40 - .47
.48 - .55
.56 - .63
.64 - .71
.72 - .79
.80 - .87
.88 - .95
.96 - 103
---------28
Step 9. Determine Our Subnet Addresses:
# Binary Subnetwork
1
0000 0000
2
0000 1000
3
000 1 0 000
4
0001 1000
5
0010 0000
6
0010 1000
7
0011 0000
8
0011 1000
9
0100 0000
10
0100 1000
11
0101 0000
12
0101 1000
13
0110 0000
..
.…….
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Range of Host #’s
Subnet Address
-----------
201.222.5.8
201.222.5.16
201.222.5.24
201.222.5.32
201.222.5.40
201.222.5.48
201.222.5.56
201.222.5.64
201.222.5.72
201.222.5.80
201.222.5.88
201.222.5.96
----------
---------------
1111 1000
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Step 10. Determine Host Addresses of the Six
Nodes of Each Subnet:
# Subnetwork Range of Host #’s Decimal Host #’s
Subnet Address
Host Address Range
1
00000
2
00001
000 - 111
.8 - .15
201.222.5.8
201.222.5.9 thru 201.222.5.14
3
00010
000 - 111
.16 - .23
201.222.5.16
201.222.5.17 thru 201.222.5.22
4
00011
000 - 111
.24 - .31 201.222.5.24
201.222.5.25 thru 201.222.5.30
5
00100
000 - 111
.32 - .39 201.222.5.32
201.222.5.33 thru 201.222.5.38
6
00101
000 - 111
.40 - .47 201.222.5.40
201.222.5.41 thru 201.222.5.46
7
00110
000 - 111
.48 - .55 201.222.5.48
201.222.5.49 thru 201.222.5.54
8
00111
000 - 111
.56 - .63 201.222.5.56
201.222.5.57 thru 201.222.5.62
9
01000
000 - 111
.64 - .71 201.222.5.64
201.222.5.65 thru 201.222.5.70
10
01001
000 - 111
.72 - .79 201.222.5.72
201.222.5.73 thru 201.222.5.78
11
01010
000 - 111
.80 - .87 201.222.5.80
201.222.5.81 thru 201.222.5.86
12
01011
000 - 111
.88 - .95 201.222.5.88
201.222.5.89 thru 201.222.5.94
13
01100
000 - 111
.96 - 103 201.222.5.96
201.222.5.97 thru 201.222.5.-..
.…….
---------------------------------------------------------------------32
11111
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Step 12: Find New Subnet mask
Based on the Class, determine the
subnet mask for network 201.222.5.0
(remember that 5 bits were borrowed):
11111111.11111111.11111111.11111 000
Network
255.
Network
255.
Network
255.
Subnet Host
248
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YOU DID IT!
NETWORK 201.222.5.0
201.222.5.11
201.222.5.18
201.222.5.10
201.222.5.22
201.222.5.12
Subnetwork
201.222.5.8
E0
201.222.5.9
Subnetwork
Router
E1
201.222.5.16
201.222.5.17
201.222.5.20
201.222.5.13
201.222.5.14
Routing Table
201.222.5.8 E0
201.222.5.16 E1
201.222.5.24 E2
201.222.5.32 E3
201.222.5.19
201.222.5.21
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•
•
•
•
•
African Network Information Centre (AfriNIC)[1] for Africa
American Registry for Internet Numbers (ARIN)[2] for the United States, Canada, and several parts of the Caribbean region.
Asia-Pacific Network Information Centre (APNIC)[3] for Asia, Australia, and neighboring countries
Latin America and Caribbean Network Information Centre (LACNIC)[4] for Latin America and parts of the Caribbean region
RIPE NCC[5] for Europe, the Middle East, and Central Asia
33