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There are 232 possible IPv4 addresses.
When the predecessor of the Internet started in the 1970s it did not seem possible that this address space would ever be exhausted.
No effort was made to allocate IP addresses carefully.
In particular:
● The classful addressing system was wasteful(224 addresses to MIT)
Background to Chapter 9 - Classless and Subnet Address Extensions (CIDR)
and Chapter 31 – A Next-Generation IP
● Every physical network had to have a unique network prefix
● Network prefixes were not allocated geographically(example – 138.26.0.0 is UAB 138.25.0.0 is in Australia)
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Comer: “In the early 1980s, as Ethernet gained popularity, it became apparent that the classful addressing scheme would have insufficient network addresses, especially class B prefixes.”
1985: Subnetting allowed organizations to share a single network prefix over multiple physical networks, which helped conserve the IPv4 address space (Comer, Chapter 9A).
1993: Shortage of IPv4 network addresses threatens, especially class B.Some geographical allocation of class-C addresses
Present situation:
● The IPv4 address space is exhausted – no new large blocks left
● Forwarding tables in the Internet backbone are very large (200,000 entries).
Supernetting/CIDR comes to the rescue, superseding “classfull” addressing (Comer, Chapter 9B).
2012 Large-scale adoption of IPv6 (Comer chapter 31)
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Figure 4.1
Figure 9.3
Subnetting class B network
Recall:
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9.16 Classless Addressing and Supernetting
Under the original “classful” addressing system IPv4 address space was becoming exhausted.
The rigid class scheme made allocation of IP addresses inefficient.
Subnet addressing (1987) helped, but problem remained.
“Temporary” solution (1993) was to abandon classes completely and let the network prefix be any length.
This is called classless IP addressing, or supernetting.
We already had the ability to do this, in the address mask!
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9.16 Classless Addressing and Supernetting - continued
Example:
Organization wants a class-B network address – none available.
256 class-C networks would have the same total number of addresses.
Problem with implementation of this: software on all external routers had to be modified.
Problem:
Outsiders would need 256 entries in their routing tables, instead of one (contrast subnetting, which is invisible to outsiders).
Solution:
Classless Inter-Domain Routing aggregates 256 contiguous class-C networks together by carrying along a netmask of 255.255.0.0 (“treat these 256 contiguous class-C networks like a class-B network”)
The network address is never mentioned without also stating the netmask.
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9.17 CIDR Address Blocks and Bit Masks
The netmask 255.255.0.0 is just one example.
The division between the network part and the host part of the IP address can be placed (almost) anywhere by an appropriate address mask.
CIDR notation:State number of bits in network part.
e.g. address mask 255.255.255.0 is CIDR /24
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9.17 CIDR Address Blocks and Bit Masks – continued
The revised forwarding algorithm remains unchanged, but is now used both internally and externally.
Figure 9.7
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9.17 CIDR Address Blocks and Bit Masks – continued
CIDR allows allocation of different sizes of address blocks.
It was introduced in the context of privatization of the Internet, which introduced Internet Service Providers (ISPs).
Using CIDR, large ISPs are allocated large address blocks, which they can then divide (using CIDR) into
smaller blocks to allocate to their customers.
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9.17 CIDR Address Blocks and Bit Masks – continued
Example:
Organization is assigned a block of 2048 addresses, based on 128.211.168.0
(notice ambiguous class – under classful system 128.211 is class-B
64K addresses allocated as a single block)
Block size is 211 addresses, which would have been 8 class C networks.
Netmask for this block is
11111111 11111111 11111000 00000000
255 . 255 . 248 . 0
CIDR /21
Refer to this allocation as 128.211.168.0 /21
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9.17 CIDR Address Blocks and Bit Masks - continued
Figure 9.9
1111
9.18 Address Blocks and CIDR Notation
Figure 9.10
Possible address masks:
Class A
Class B
Class C
/31 and /32 useless!
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9.19 A Classless Addressing Example
A large ISP has been allocated the entire class-B address 128.211.0.0
i.e. 128.211.0.0 /16
Large ISP has allocated the address block shown previously to a smaller ISP,
i.e. 128.211.168.0 /21
So smaller ISP has available
128.211.168.0128.211.169.0128.211.170.0128.211.171.0128.211.172.0128.211.173.0128.211.174.0128.211.175.0
128.211.10101000.00000000
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9.19 A Classless Addressing Example - continued
128.211.168.0 /21
Expands to:
3rd octet 4th octet
128.211.168.0 10101 000 00000000
128.211.169.0 10101 001
128.211.170.0 10101 010
128.211.171.0 10101 011
128.211.172.0 10101 100
128.211.173.0 10101 101
128.211.174.0 10101 110
128.211.175.0 10101 111
128.211.168.0/22
128.211.172.0/23
/24
/24
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1024 addresses
128.211.168.0/22
512 addresses
128.211.172.0/23
256 addresses
128.211.174.0/24
256 addresses128.211.175.0/24
The smaller ISP could further partition 128.211.175.0/24
Smaller ISP has been allocated 128.211.168.0/21 Can allocate partitions to customers:
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9.19 A Classless Addressing Example - continued
Figure 9.11
An ISP owning 128.211.0.0/16 might assign an individual needing only two IP addresses
128.211.176.212 /30
The two IP usable addresses are:
128.211.176.213
and 128.211.176.214
(note that this is not in the range of the previous example)
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9.19 A Classless Addressing Example - continued
Classless addressing, which is now used throughout the Internet, treats IP addresses as arbitrary integers, and allows a network administrator to partition addresses into contiguous blocks, where the number of addresses in a block is a power of 2.
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9.21 Longest-Match and Mixtures of Route Types
Consider the smaller ISP’s routers – entry router is R0
From R0 assume that all networks except 128.211.175.0 /24 are reached
through router R1 and 128.211.175.0 /24 is reached through R2
Fwd to R1
Fwd to R2
3rd octet 4th octet
128.211.168.0 10101 000 00000000 128.211.169.0 10101 001 128.211.170.0 10101 010 128.211.171.0 10101 011 128.211.172.0 10101 100 128.211.173.0 10101 101 128.211.174.0 10101 110
128.211.175.0 10101 111
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1024 addresses
128.211.168.0/22
512 addresses
128.211.172.0/23
256 addresses
128.211.174.0/24
256 addresses128.211.175.0/24
9.19 A Classless Addressing Example – continued Smaller ISP has been allocated 128.211.168.0/21
R2
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3rd octet R0 table entry
128.211.168.0 10101 000128.211.169.0 10101 001128.211.170.0 10101 010128.211.171.0 10101 011128.211.172.0 10101 100128.211.173.0 10101 101128.211.174.0 10101 110
9.21 Longest-Match and Mixtures of Route Types – continued
128.211.175.0 10101 111
128.211.168.0/21 to R1
128.211.175.0/24 to R2
Nothing gets forwarded to R2
2020
9.21 Longest-Match and Mixtures of Route Types – continued
Figure 9.14
All traffic will be sent to 10.0.0.2
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9.21 Longest-Match and Mixtures of Route Types – continued
Conclusion:
We need another modification to the forwarding algorithm:
Forward on basis of longest match in routing table
Can help by putting the most specific routes first.
2222
9.22 CIDR Blocks Reserved for Private Networks
Figure 9.15
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Regional Internet Registries
IP Address Allocation: Internet Assigned Numbers Authority
“owns” the entire IPv4 and IPv6 address space!
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Allocation of IP addresses (IPv4 and IPv6)
mentioned briefly in Comer’s chapter 4
ARIN
Large ISP
Large end-user or small ISP
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Exhaustion of IPv4 Address Space
February 01, 2011
The Internet Assigned Numbers Authority (IANA) assigned two of the remaining blocks of IPv4 addresses - each containing 16.7 million addresses - to the Asia Pacific Network Information Centre (APNIC) on Tuesday. This action sparks an immediate distribution of the remaining five blocks of IPv4 address space, with one block going to each of the five Regional Internet Registries (RIR).
The American Registry for Internet Numbers (ARIN), which doles out IPv4 addresses to carriers and other network operators in North America, is expected to receive its last allotment of IPv4 addresses today. Experts say it will take anywhere from three to seven months for the registries to distribute the remaining IPv4 addresses to carriers.
No more new blocks of IPv4 addresses!
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Advent of IPv6: World IPv6 Day, 2011
On 8 June, 2011, top websites and Internet service providers around the world, including Google, Facebook, Yahoo!, Akamai and Limelight Networks joined together with more than 1000 other participating websites in World IPv6 Day for a successful global-scale trial of the new Internet Protocol, IPv6.
By providing a coordinated 24-hour “test flight”, the event helped demonstrate that major websites around the world are well-positioned for the move to a global IPv6-enabled Internet, enabling its continued exponential growth.
World IPv6 Launch, 2012
Major ISPs, home networking equipment manufacturers, and web companies around the world are coming together to permanently enable IPv6 for their products and services by 6 June 2012.
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31.6 Features of IPv6
● Larger Addresses (128-bit)
● Extended Address Hierarchy
● Flexible Header Format
● Improved Options
Not backward compatible with IPv4! Operate Dual stacks
Chapter 31 - A Next Generation IP (IPv6)
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Recall IPv4 Datagram Header Format
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31.7 General Form of an IPv6 Datagram
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4
6
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31.8 IPv6 Base Header Format
Changes from IPv4
● Alignment has been changed from 32-bit to 64-bit
● Header Length field has been replaced by Payload Length (base header fixed length of 40 bytes)
●Address fields now 16 octets (128-bits)
● Fragmentation information moved out of fixed header into extension
● TIME-TO-LIVE replaced by HOP LIMIT
● SERVICE TYPE field renamed TRAFFIC CLASS and extended with a FLOW LABEL field
● PROTOCOL field replaced by NEXT HEADER field
● No HEADER CHECKSUM field
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31.10 Parsing an IPv6 Datagram
Simple case:
Hop-by-hop headers precede end-to-end headers.
If source routing specified:
If Payload Authentication also specified:
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31.11 IPv6 Fragmentation and Reassembly – omit
31.12 Consequences of End-to-End Fragmentation - omit
31.13 IPv6 Source Routing - omit
31.14 IPv6 Options - omit
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31.15 Size of the IPv6 Address Space
296 times bigger than IPv4 address space!
1024 addresses per square meter of the earth’s surface!
Every person on the planet can have a private internet the size of the present global Internet.
Assigning all possible addresses at a rate of one million
million per sec would take 1020 years.
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31.16 IPv6 Colon Hexadecimal Notation
Consider 128-bit address in dotted-decimal form:
104.230.140.100.255.255.255.255.0.0.17.128.150.10.255.255
Same 128-bit address in colon-hexadecimal form:
8 groups of 16 bits
68E6:8C64:FFFF:FFFF:0:1180:96A:FFFF
Compression:
FF05:0:0:0:0:0:0:B3
written as FF05::B3
(left-align what is to left of :: right-align what is to right)
CIDR-like: 12AB::CD30:0:0:0:0 /60
means high-order 60 bits of address are (hexadecimal) 12AB00000000CD3
In binary starts with
0110 1000 . 1110 0110 . 1000 1100 . 0110 0100 . 1111 1111 . 1111 1111 . . .
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31.17 Three Basic IPv6 Address Types
31.18 Duality of Broadcast and Multicast – omit
31.19 Engineering Choice and Simulated Broadcast - omit
● Anycast “The destination is a set of computers, possibly at different locations, that all share a single address; the datagram
should be routed along a shortest path and delivered to exactly one of the group (i.e. the closest member) (used to duplicate DNS root servers under single IP address)
● Multicast
● Unicast
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31.20 Proposed IPv6 Address Space Assignment
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31.21 Embedded IPv4 Addresses and Transition
The 16-bit field contains 0000 if the host also has a “conventional” IPv6 address, FFFF if it does not.
Transition: expect to run dual IPv4 IPv6 stacks for many years
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31.22 Unspecified and Loopback Addresses
0:0:0:0:0:0:0:0 is an unspecified address
(used at startup of a machine that does not yet have
an assigned IPv6 address – same in IPv4)
0:0:0:0:0:0:0:1 is the loopback address
(like 127.0.0.0 in IPv4)
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31.23 Unicast Address Structure
This will be a replacement for Comer’s treatment
The replacement is based on a document by the American Registry for Internet Numbers (ARIN), September 2010.
As stated earlier, authority for allocation of IPv6 addresses flows down the same hierarchy as IPv4:
ARIN
Large ISP
Large end-user or small ISP
Internet Assigned Numbers Authority
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Repeat Figure 31.8 (upper)
The left half (64 bits) of the 128-bit address will be the Global Routing address, the right half of the address will be the Interface Identifier (i.e. MAC address)
We now consider the further assignment of the leftmost 64 bits.
4343
3 bits 61 bits
0 0 1 managed by IANA
3 20 41
Allocated by IANA
0 0 1 to ARIN managed by ARIN
3 20 9 32
Allocated by IANA Allocated by
0 0 1 to ARIN ARIN to large ISP managed by large ISP
3 20 9 16 16
Allocated by IANA Allocated by Assigned by ISP managed by
0 0 1 to ARIN ARIN to large ISP to large end-site end-site
Assignment of IPv6 unicast addresses
/3
/23
/32
/48
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3 20 9 16 16
Allocated by IANA Allocated by Assigned by ISP managed by
0 0 1 to ARIN ARIN to large ISP to large end-site end-site
3 20 9 24 8
Allocated by IANA Allocated by Assigned by ISP mgd. by
0 0 1 to ARIN ARIN to large ISP to small end-site end-site
3 20 9 32
Allocated by IANA Allocated by Assigned by ISP
0 0 1 to ARIN ARIN to large ISP to end-user
/48
/56
/64
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The A-root server provides an example of IPv6 unicast addressing.
IANA allocated ARIN this block of unicast IPv6 addresses:
2001: 400: /23
0010 0000 0000 0001 0000 0100 0000 0000 …..
High-order 23 bits allocated TO ARIN, rest of address assigned BY ARIN
A-root server IPv6 address:
2001: 503: ba3e: [ 0: 0: 0: 2: 30]
0010 0000 0000 0001 0000 0101 0000 0011 1011 1010 0011 1110 …..
The A-root server IPv6 address was assigned by ARIN.
Similarly, the K-root server IPv6 address was assigned by RIPE.
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The expanded address space allows the interface hardware (MAC) address to be embedded in the IPv6 address.
31.24 Interface Identifiers
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31.24 Interface Identifiers – contd.
The EUI-64 standard specifies how a 48-bit Ethernet address can be expanded to 64 bits.
Recall that the high-order 24 bits identify the manufacturer (“company”)
Low order 24 bits are serial number (“manufacturer’s extension”)
Fig 31.11
This is used in IPv6 Link-Local Addresses
F F F E
4848
31.25 Local Addresses
“In addition to the global unicast addresses described above, IPv6 includes prefixes for unicast addresses that have local scope …”
These are link-local addresses restricted to the local network (IPv6 datagrams so addressed cannot cross a router).
The first 10 bits are (from fig. 31.8)
1111 1110 10
If the following 6 bits are zero, this would be hexadecimal FE80
The low-order 64 bits encode the interface’s hardware address
Example from network lab machine F1:
Ethernet address: 00:B0:D0:63:5B:92
Link-local address: FE80::2B0:D0FF:FE63:5B92
No need for ARP in IPv6!
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Ethernet address: 00:B0:D0:63:5B:92Link-local address: FE:80::2B0:D0FF:FE63:5B92
00000010
F F F E 6 3 5 B 9 2B 0 D 0 0 2
So the complete IPv6 address of eth1 on F1 is
FE:80::2B0:D0FF:FE63:5B92
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31.26 Autoconfiguration and Renumbering -omit
END OF COURSE
MATERIAL!!!
5151
Exam #3
Will be held on Tuesday, May 8
From 9:30 to 10:30am
CS 534 term papers due then
