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Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

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Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008
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Page 1: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Addressing: IPv4, IPv6, and Beyond

CS 4251: Computer Networking IINick FeamsterSpring 2008

Page 2: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

IPv4 Addresses: Networks of Networks

• 32-bit number in “dotted-quad” notation

– www.cc.gatech.edu --- 130.207.7.36

10000010 11001111 00000111 00100100

Network (16 bits) Host (16 bits)

130 207 7 36

• Problem: 232 addresses is a lot of table entries

• Solution: Routing based on network and host

– 130.207.0.0/16 is a 16-bit prefix with 216 IP addresses

Topological Addressing

Page 3: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Pre-1994: Classful Addressing

Network ID Host ID

8 16

Class A

32

0

Class B 10

Class C 110

Multicast AddressesClass D 1110

Reserved for experimentsClass E 1111

24

/8 blocks (e.g., MIT has 18.0.0.0/8)

/16 blocks (e.g., Georgia Tech has 130.207.0.0/16)

/24 blocks (e.g., AT&T Labs has 192.20.225.0/24)

Simple Forwarding: Address range specifies network ID length

Page 4: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Problem: Routing Table Growth

• Growth rates exceeding advances in hardware and software capabilities

• Primarily due to Class C space exhaustion• Exhaustion of routing table space was on the horizon

Source: Geoff Huston

Page 5: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Routing Table Growth: Who Cares?

• On pace to run out of allocations entirely

• Memory– Routing tables – Forwarding tables

• “Churn”: More prefixes, more updates

Page 6: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Possible Solutions

• Get rid of global addresses– NAT

• Get more addresses– IPv6

• Different aggregation strategy– Classless Interdomain routing

Page 7: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Classless Interdomain Routing (CIDR)

IP Address: 65.14.248.0 “Mask”: 255.255.252.0

01000001 00001110 11111000 00000000

11111111 11111111 11111100 00000000

Use two 32-bit numbers to represent a network. Network number = IP address + Mask

Example: BellSouth Prefix: 65.14.248.0/22

Address no longer specifies network ID range.New forwarding trick: Longest Prefix Match

Page 8: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Benefits of CIDR

• Efficiency: Can allocate blocks of prefixes on a finer granularity

• Hierarchy: Prefixes can be aggregated into supernets. (Not always done. Typically not, in fact.)

Customer 1

Customer 2

AT&T Internet

12.20.249.0/24

12.20.231.0/2412.0.0.0/8

Page 9: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

1994-1998: Linear Growth

• About 10,000 new entries per year• In theory, less instability at the edges (why?)

Source: Geoff Huston

Page 10: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Around 2000: Fast Growth Resumes

Claim: remaining /8s will be exhausted within the next 5-10 years.

T. Hain, “A Pragmatic Report on IPv4 Address Space Consumption”, Cisco IPJ, September 2005

Page 11: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Fast growth resumes

Rapid growth in routing tables

Dot-Bomb Hiccup

Significant contributor: Multihoming

Source: Geoff Huston

Page 12: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Multihoming Can Stymie Aggregation

• “Stub AS” gets IP address space from one of its providers• One (or both) providers cannot aggregate the prefix

12.20.249.0/24

AT&T Verizon

Verizon does not “own” 10.0.0.0/16. Must advertise

the more-specific route.

Mid-Atlantic Corporate Federal

Credit Union (AS 30308)

12.20.249.0/24

12.20.249.0/24

Page 13: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

The Address Allocation Process

• Allocation policies of RIRs affect pressure on IPv4 address space

IANA

AfriNIC APNIC ARIN LACNIC RIPE

http://www.iana.org/assignments/ipv4-address-space

Georgia Tech

Page 14: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

/8 Allocations from IANA

• MIT, Ford, Halliburton, Boeing, Merck• Reclaiming space is difficult. A /8 is a bargaining chip!

Page 15: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Address Space Ownership% whois -h whois.arin.net 130.207.7.36[Querying whois.arin.net][whois.arin.net]

OrgName: Georgia Institute of TechnologyOrgID: GITAddress: 258 Fourth St NWAddress: Rich BuildingCity: AtlantaStateProv: GAPostalCode: 30332Country: US

NetRange: 130.207.0.0 - 130.207.255.255CIDR: 130.207.0.0/16NetName: GITNetHandle: NET-130-207-0-0-1Parent: NET-130-0-0-0-0NetType: Direct AssignmentNameServer: TROLL-GW.GATECH.EDUNameServer: GATECH.EDUComment:RegDate: 1988-10-10Updated: 2000-02-01

RTechHandle: ZG19-ARINRTechName: Georgia Institute of TechnologyNetwork ServicesRTechPhone: +1-404-894-5508RTechEmail: [email protected]

OrgTechHandle: NETWO653-ARINOrgTechName: Network OperationsOrgTechPhone: +1-404-894-4669

- Regional Internet Registries (“RIRs”)- Public record of address allocations- ISPs should update when delegating address space- Often out-of-date

Page 16: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

IPv6 and Address Space Scarcity

• 128-bit addresses– Top 48-bits: Public Routing Topology (PRT)

• 3 bits for aggregation• 13 bits for TLA (like “tier-1 ISPs”)• 8 reserved bits• 24 bits for NLA

– 16-bit Site Identifier: aggregation within an AS– 64-bit Interface ID: 48-bit Ethernet + 16 more bits

– Pure provider-based addressing• Changing ISPs requires renumbering

Page 17: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Header Formats

IPv4

Page 18: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Summary of Fields

• Version (4 bits) – only field to keep same position and name• Class (8 bits) – new field• Flow Label (20 bits) – new field• Payload Length (16 bits) – length of data, slightly different from

total length• Next Header (8 bits) – type of the next header, new idea• Hop Limit (8 bits) – was time-to-live, renamed• Source address (128 bits)• Destination address (128 bits)

Page 19: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

IPv6: Claimed Benefits

• Larger address space• Simplified header• Deeper hierarchy and policies for network

architecture flexibility • Support for route aggregation • Easier renumbering and multihoming• Security (e.g., IPv6 Cryptographic Extensions)

Page 20: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

IPv6 Flows

• Traffic can be labeled with particular flow identifier for which a sender can expect special handling (e.g., different priority level)

Page 21: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

IPv6: Deployment Options

• IPv4 Tunnels• Dual-stack• Dedicated Links• MPLS

Routing Infrastructure

Applications

• IPv6-to-IPv4 NAPT• Dual-stack servers

Page 22: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

IPv6 Deployment Status

Big users: Germany (33%), EU (24%), Japan (16%), Australia (16%)

Page 23: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Transitioning: Dual-Stack

• Dual-Stack Approach: Some nodes can send both IPv4 and IPv6 packets– Dual-stack nodes must determine whether a node is

IPv6-capable or not– When communicating with an IPv4 node, an IPv4

datagram must be used

Page 24: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Transitioning: IPv6 over IPv4 Tunnels

http://www.cisco.com/en/US/tech/tk872/technologies_white_paper09186a00800c9907.shtml

One trick for mapping IPv6 addresses: embed the IPv4 address in low bits

Page 25: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Reality: “96 More Bits, No Magic”

• No real thought given to operational transition• IPv6 is not compatible with IPv4 on the wire

– Variable-length addressing could have fixed this, but…

• Routing load won’t necessarily be reduced– TE Model is the same– Address space fragmentation will still exist

• The space is not infinite: 64 bits to every LAN• Not necessarily better security• Routers don’t fully support all IPv6 features in hardware

Page 26: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Another extension: Security (IPSec)

• Backwards compatible with IPv4• Transport mode: Can be deployed only at

endpoints (no deployment at routers needed)– Encrypted IP payload encapsulated within an

additional, ordinary IP datagram

• Provides– Encryption of datagram– Data Integrity– Origin authentication

Page 27: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Architectural Discontents

• Lack of features– End-to-end QoS, host control over routing, end-to-

end multicast,…

• Lack of protection and accountability– Denial-of-service (DoS)

• Architecture is brittle

Page 28: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Architectural Brittleness

• Hosts are tied to IP addresses– Mobility and multi-homing pose problems

• Services are tied to hosts– A service is more than just one host: replication,

migration, composition

• Packets might require processing at intermediaries before reaching destination– “Middleboxes” (NATs, firewalls, …)

Page 29: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Internet Naming is Host-Centric

• Two global namespaces: DNS and IP addresses

• These namespaces are host-centric– IP addresses: network location of host– DNS names: domain of host– Both closely tied to an underlying structure– Motivated by host-centric applications

Page 30: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Trouble with Host-Centric Names

• Host-centric names are fragile– If a name is based on mutable properties of its

referent, it is fragile– Example: If Joe’s Web page

www.berkeley.edu/~hippie moves to www.wallstreetstiffs.com/~yuppie, Web links to his page break

• Fragile names constrain movement– IP addresses are not stable host names– DNS URLs are not stable data names

Page 31: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

Solution: Name Services and Hosts Separately

• Service identifiers (SIDs) are host-independent data names

• End-point identifiers (EIDs) are location-independent host names

• Protocols bind to names, and resolve them– Apps should use SIDs as data handles– Transport connections should bind to EIDs

Page 32: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

The Naming Layers

User-level descriptors(e.g., search)

App session

App-specific search/lookupreturns SID

Transport

Resolves SID to EIDOpens transport conns

IP

Resolves EID to IP

Bind to EID

Use SID as handle

IP hdr EID TCP SID …IP

Transport

App session

Application

Page 33: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

SIDs and EIDs should be Flat

• Flat names impose no structure on entities– Structured names stable only if name structure matches

natural structure of entities– Can be resolved scalably using, e.g., DHTs

• Flat names can be used to name anything– Once you have a large flat namespace, you never need

other global “handles”

Page 34: Addressing: IPv4, IPv6, and Beyond CS 4251: Computer Networking II Nick Feamster Spring 2008.

ResolutionService

Flat Names: Flexible Migration

<A HREF=http://f012012/pub.pdf>here is a paper</A>

<A HREF=http://f012012/pub.pdf>here is a paper</A>

HTTP GET:

/docs/pub.pdf

10.1.2.3

/docs/

20.2.4.6

HTTP GET:

/~user/pubs/pub.pdf(10.1.2.3,80,/docs/)(20.2.4.6,80,

/~user/pubs/)/~user/pubs/

• SID abstracts all object reachability information• Objects: any granularity (files, directories)• Benefit: Links (referrers) don’t break

Domain H

Domain Y


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