Understanding Internet Architecture and Addressing

1
Understanding Internet Architecture and Addressing

• Prof. Gao
• ECE697J Spring 2005
• Advanced Computer Networks

2
Outline

• Internet Architecture
• Classless Inter-Domain Routing (CIDR)
• Scaling IP address space

3
Whats the Internet nuts and bolts view

• millions of connected computing devices hosts,
  end-systems
• PCs workstations, servers
• PDAs, phones, toasters
• running network apps
• communication links
• fiber, copper, radio, satellite
• routers forward packets (chunks) of data thru
  network

4
Internet protocol stack

• application supporting network applications
• ftp, smtp, http
• transport host-to-host data transfer services
• tcp, udp
• network routing of datagrams from source to
  destination
• ip, routing protocols
• link data transfer between neighboring network
  elements
• ppp, ethernet
• physical bits on the wire

5
Network layer functions

• transport packet from sending to receiving hosts
• network layer protocols in every host, router
• two important functions
• path determination route taken by packets from
  source to dest. Routing algorithms
• switching move packets from routers input to
  appropriate router output

6
Datagram networks the Internet model

• no call setup at network layer
• routers no state about end-to-end connections
• no network-level concept of connection
• packets typically routed using destination host
  ID
• packets between same source-dest pair may take
  different paths

1. Send data
2. Receive data
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Network Core Packet Switching

• resource contention
• aggregate resource demand can exceed amount
  available
• congestion packets queue, wait for link use
• store and forward packets move one hop at a time
• transmit over link
• wait turn at next link

• each end-end data stream divided into packets
• user A, B packets share network resources
• each packet uses full link bandwidth
• resources used as needed,

8
Network Core Packet Switching
10 Mbs Ethernet
C
A
statistical multiplexing
1.5 Mbs
B
queue of packets waiting for output link
45 Mbs

• Packet-switching versus circuit switching human
  restaurant analogy
• other human analogies?

9
Evolution of the Internet
1986-1995
Regional Backbone
Regional Backbone
Campus Network

NSFNET Backbone
Regional Backbone
Regional Backbone
10
Internet Today
NSFNET decommissioned in 1995 commercialization
of the Internet
(Inter)National Provider
NAP
Private Peering
Regional Provider
(Inter)National Provider
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Network Access Point (NAP)

• MAE-East
• MAE-West
• Sprint NAP

ATT
MCI
FDDI Ring/ATM Switch
vBNS
12
Private Peering
Exchange Traffic
ATT
MCI
13
Internet Architecture

• Segregated to Autonomous Systems (ASes) belong to
  
• ISPs
• Companies
• Universities
• One ISP might own several ASes
• ISP Merger

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Inter-AS and Intra-AS Routing
AS2
AS1
Inter-AS routing
Intra-AS routing
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Why different Inter-AS and Intra-AS routing
protocols?

• Administrative each AS runs different intra-AS
  routing protocol
• Policy AS has commercial agreement that
  determines routing policy
• Scalability or hierarchy hiding information
  within AS reduces the routing message size.

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Forwarding Table
Inter-AS Routing
Routing Table
Intra-AS Routing
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Inter-AS Routing Protocols

• Use EGP in NSFNET
• Border Gateway Protocol (BGP)
• BGP-4 de facto standard
• Path Vector Algorithm

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Intra-AS Routing

• Routing Information Protocol (RIP)
• Distance Vector Algorithm
• Open Shortest Path First (OSPF)
• Link State Algorithm
• IS-IS
• Link State Algorithm

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Border Gateway Protocol (BGP)

• Exchange reachability information
• Apply local policies for announcing and
  selecting route
• Avoid Route Loops
• Incremental Update
• Use TCP

AS701
(1), (7018,1)
MCI
AS7018
AS1
(1), (701, 1)
ATT
BBN
1.2.3.0/24
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What is IP Address?
cnn.com
Host 3
HTTP, FTP, SMTP, TELNET, etc
TCP, UDP
IP
PPP, Ethernet
www.ecs.umass.edu 128.119.91.192
Host 2
Host 1
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IP Address

• Represent network interface
• IPv4, defined by 4 bytes (32 bits)
• Dotted-Decimal Notation
• 128.119.91.173 (sisko.ecs.umass.edu)
• 66.218.71.198 (www.yahoo.com)
• Address spaces
• 0.0.0.0 255.255.255.255
• 232 4,294,967,296 hosts

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History

• Classful IP address
• DEC 128 . 119 . 91 . 173
• BIN 10000000 . 01110111 . 01011011 . 10101101
• Class A
• 0xxxxxxx . yyyyyyyy . yyyyyyyy . yyyyyyyy
• Class B
• 10xxxxxx . xxxxxxxx . yyyyyyyy . yyyyyyyy
• Class C
• 110xxxxx . xxxxxxxx . xxxxxxxx . yyyyyyyy
• Class D and Class E
• Class D starts with 1110xxxx..., used for
  multicast
• Class E starts with 1111xxxx..., used for
  experiments
• Note xxxx network number yyyy host number

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Reserved IP Addresses

• 0.0.0.0
• Default route
• 127.0.0.1
• Loopback IP address
• Test IPC on local machine
• All bits are 0 in host number
• Denote this network
• All bits are 1 in host number
• Broadcast address in this network
• Private IP addresses
• 10.xxx.xxx.xxx, 192.168.xxx.xxx

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Prefixes and Partition of IP Addresses

• Class A networks (/8) 8-bit network prefix
• Prefix 3.0.0.0/8
• Hosts 3.0.0.0 3.255.255.255
• 16,777,216 hosts (Too big?)
• Class B networks (/16) 16-bit network prefix
• Prefix 128.119.0.0/16
• Hosts 128.119.0.0 128.119.255.255
• Class C networks (/24) 24-bit network prefix
• Prefix 202.63.28.0/24
• Hosts 202.63.28.0 202.63.28.255
• Only 255 hosts (Too small?)

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Problems with Classful Addresses
Growth of Internet Routing tables
Allocated network numbers

• Running out of IP address space?
• Exponential growth of networks and inefficient
  allocation of IP addresses
• Class A 16777215 hosts/network too big
• Class C 254 hosts/network too small

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Challenge and Solution

• For large ISPs
• Own class A address blocks
• Hard to organize IP addresses
• For small enterprises
• Own a bunch of class C address blocks
• Hard to manage so many prefixes
• Two approaches
• Classless Inter-Domain Routing (CIDR)
• Subneting and Variable Length Subnet Masks (VLSM)

27
Classless Inter-Domain Routing (CIDR)

• No concept of Class A, Class B, and Class C
  network addresses
• Rapid deployed in 1994/95
• Prefixes are not restricted to /8, /16 and /24
• Prefixes could be any length from 1 to 32
• xxx.xxx.xxx.xxx/masklength
• 1lt masklength lt32

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Prefixes and Hosts

• For example, prefix 128.119.96.0/20
• 10000000.01110111.11000000.00000000
• network number host number
• First 20 bits denote network number
• 128.119.96.0
• There are 212 4096 Hosts
• From 128.119.96.0 to 128.119. 207.255
• 10000000.01110111.11000000.00000000
  10000000.01110111.11001111.11111111

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Benefit of CIDR (1)

• CIDR promotes the efficient allocation of the
  IPv4 address space
• Divide old class A IP address into several
  reasonable size of IP prefixes
• 3.0.0.0/8 ? 3.1.10.0/24, 3.2.96.0/20,
• Aggregate several class C IP addresses into one
  reasonable sized prefix
• 202.64.28.0/24, 202.64.29.0/24
• 202.64.28.0/23
• 203.72.174.0/24, 203.72.175.0/24,
  203.72.176.0/24, 203.72.177.0/24
• 203.72.172.0/22

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Benefit of CIDR (2)

• Controlling the Growth of Internet's Routing
  Tables
• Route 1 longest prefix most specific

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Several Basic Questions

• Who manages the IP address?
• Three regional routing registries.
  
• North and South America American Registry for
  Internet Number (ARIN)
• Europe Reseaux IP Europeans (RIPE)
• Asia Asia Pacific Network Information Center
  (APNIC)
• How do you obtain IP addresses?
• ISP buys from registries or from their provider
• Buy IP addresses from your provider
• Keep your IP address when you switch to another
  provider
• Rent IP address from your provider
• Return the IP address to your provider when you
  switch to another provider

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Advantage of Hierarchical Address Allocation
Routing Aggregation, Reduce growth of routing
table size.
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Switching ISP

• Once organization A switchs its provider, it
  returns IP addresses Provider 1 and obtains a
  new address from Provider 2.
• No impact to global routing table
• But renumbering in organization A can be
  difficult

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Switching ISP without renumbering

• Retain old address, Provider 2 advertises
  exception
• No need to renumber in organization A
• But it increases the size of routing tables.

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Multihoming

• Having multiple providers

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Longest Prefix Matching

• Routes in routing table
• 1st 0.0.0.0/0 eth0 (default)
• 2nd 128.119.0.0/16 eth1
• 3rd 128.119.96.0/20 eth2
• 4st 3.0.0.0/8 eth0
• 2nd prefix covers 3rd prefix
• 3rd prefix is more specific than 2nd prefix
• For destination IP address
• 128.119.0.203, choose eth1
• 128.119.96.47, choose eth2
• Longest prefix matching
• Choose route of more specific matching prefix
• Otherwise, it choose default route

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Second-level of Address Hierarchy Subnetting

• Idea Add one more level (subnet number) to the
  class hierarchy
• Divide host number into smaller pieces

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Subnetting

• Goal
• Simple to Manage IP address in one enterprise
• Umass owns IP space 128.119.0.0/16
• Many departments
• ECS, CS, Physics, OIT
• Host IP address
• From 10000000.01110111.00000000.00000000
• To 10000000.01110111.11111111.11111111
• Define subnet
• 10000000.01110111.xxxxx000.00000000
• subnet

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Subneting

• Mapping subnet to different departments
• 01010 gt ECS department
• 10000000.01110111.01010000.00000000
• Subnet 128.119.80.0/21
• 00101 gt CS department
• 10000000.01110111.00101000.00000000
• Subnet 128.119.40.0/21

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Benefit of Subnetting

• Control routing table size
• Flexible for local network administrator
• Hide route flapping from outside routers

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Variable Length Subnet Masks(VLSM)

• ECS owns more computers than physics department
• VLSM scheme
• ECS department
• 10000000.01110111.01010000.00000000
• Prefix 128.119.80.0/21
• Physics Science department
• 10000000.01110111.11011000.00000000
• Prefix 128.119.216.0/26
• Food Science department
• 10000000.01110111.11011000.01100000
• Prefix 128.119.216.96/27

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Benefit of VLSM (1)

• Efficiency
• Easy to organize IP address space
• Recursively divided into sub-2 nets and so on
• Minimize the impact of broadcast traffic

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Benefit of VLSM (2)

• Reduce Routing Table Size
• Route Aggregation
• Summarize all its lower level hierarchies into a
  single advertisement

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Subnet Design Example

• An organization has been assigned the network
  number 140.25.0.0/16
• Needs to create a set of subnets that supports up
  to 60 hosts on each subnet
• Step 1 Define the Subnet Mask / Extended-Prefix
  Length
• 26-2 62, no room for expansion 27-2 126
• Step 2 Define subnet length and subnet numbers
• Step 3 Define Hosts addresses for each subnet
• Step 4 Define the broadcast address for each
  subnet

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Requirements of VLSM

• Routing protocol must carry extended-network
  prefix information
• OSPF, I-IS-IS, IGP, RIP2
• RIP1 does not support this
• Forwarding algorithm based on the longest
  prefixes match

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VLSM vs. CIDR

• Similarity
• Recursively dividing network into small sub
  networks
• Differences
• VLSM
• Recursion is performed on the address space
  previously assigned to an organization
• Invisible to the global Internet
• CIDR
• Recursive allocation of an address block by an
  Internet Registry to any large ISP or small
  companies
• Visible to the global Internet

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Growth of Routing Tables
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Growth of Routing Tables

• CIDR is deployed in 19941995
• The growth around 19971998 is significant slow
• Since 1998, routing table grows quickly
• Reachability and Connectivity
• Multi-Homing
• Traffic Engineering
• Load balancing
• More specific prefixes
• Failure to aggregation
• Any other reasons ?

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Multi-Homing

• Network A has two ISPs
• Once route R1 fails, network A still can connect
  to Internet through R2.

R
64.73.0.0/18 130.23.56.0/24
130.23.0.0/16
Backup Provider 64.73.0.0/18
Primary Provider 130.23.0.0/16
R1
R2
A 130.23.56.0/24
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Traffic Engineering

• Network A announces two routes to Provider B
• For route R, traffic to 130.23.0.0/16 -
  130.23.80.0/20 goes through A
• But for traffic to 130.23.82.0/24, it goes
  through B

64.73.0.0/18 130.23.80.0/20 130.23.82.0/24
R
130.23.0.0/16
Provider B 64.73.0.0/18
Provider A 130.23.0.0/16
R1
R2
130.23.80.0/20
130.23.80.0/20 130.23.82.0/24
130.23.82.0/24
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Some Solutions to IP addressExhaustion

• IPv6 or IPng
• 16 bytes (128-bits) IP address
• Appeal to Return Unused IP Network Prefixes
• Address Allocation for Private Internets
• 10.0.0.0 10.255.255.255
• 172.16.0.0 172.31.255.255
• 192.168.0.0 192.168.255.255
• Implications of Address Allocation Policies
• Procedures for Internet/Enterprise Renumbering
  (PIER)
• Market-Based Allocation of IP Address Blocks

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Network Address Translations (NAT)

• Private IP address can be re-used by different
  organization
• R1 and R2 translate private IP addresses into
  their own IP address
• Problem Break down End-to-End principle in
  Internet

Global IP address
R1
192.168.0.0/16
R2
192.168.0.0/16
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Translating MAC/IP/Domain-Name

• Mapping between IP address and MAC address
• MAC address
• 48-bit Ethernet address
• ARP protocol
• Broadcast IP packet to get MAC address from IP
  address
• Documented in RFC 826
• Mapping between domain name and IP address
• Domain Name www.ecs.umass.edu
• IP address 128.119.91.192
• DNS
• Internet directory service
• Translate between domain names and IP addresses

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Summary

• IP Address
• Universal ID
• Scalability
• Address aggregation
• two level hierarchy with physical constraints
• Management
• Data forwarding performance
• Other proposals
• Separate IP level name from IP address
• Multiple addresses for multihomed hosts