3 IPv4 Addresses: Networks of Networks Topological Addressing32-bit number in “dotted-quad” notation130207736Network (16 bits)Host (16 bits)Problem: 232 addresses is a lot of table entriesSolution: Routing based on network and host/16 is a 16-bit prefix with 216 IP addresses
4 Pre-1994: Classful Addressing 3281624Class ANetwork IDHost ID/8 blocks (e.g., MIT has /8)Class B10/16 blocks (e.g., Georgia Tech has /16)Class C110/24 blocks (e.g., AT&T Labs has /24)Class DMulticast Addresses1110Class E1111Reserved for experimentsSimple Forwarding: Address range specifies network ID length
6 Problem: Routing Table Growth Source: Geoff HustonGrowth rates exceeding advances in hardware and software capabilitiesPrimarily due to Class C space exhaustionExhaustion of routing table space was on the horizon
7 Routing Table Growth: Who Cares? On pace to run out of allocations entirelyMemoryRouting tablesForwarding tables“Churn”: More prefixes, more updates
8 Possible Solutions Get rid of global addresses Get more addresses NATGet more addressesIPv6Different aggregation strategyClassless Interdomain routing
9 Classless Interdomain Routing (CIDR) Use two 32-bit numbers to represent a network.Network number = IP address + MaskExample: BellSouth Prefix: /22IP Address: “Mask”:Address no longer specifies network ID range. New forwarding trick: Longest Prefix Match
10 1994-1998: Linear Growth About 10,000 new entries per year Source: Geoff HustonAbout 10,000 new entries per yearIn theory, less instability at the edges (why?)
11 Around 2000: Fast Growth Resumes T. Hain, “A Pragmatic Report on IPv4 Address Space Consumption”, Cisco IPJ, September 2005Claim: remaining /8s will be exhausted within the next 5-10 years.
12 Significant contributor: Multihoming Rapid growth in routing tables Fast growth resumesSignificant contributor: MultihomingDot-Bomb HiccupRapid growth in routing tablesSource: Geoff Huston
13 The Address Allocation Process IANAAfriNICAPNICARINLACNICRIPEGeorgia TechAllocation policies of RIRs affect pressure on IPv4 address space
14 /8 Allocations from IANA MIT, Ford, Halliburton, Boeing, MerckReclaiming space is difficult. A /8 is a bargaining chip!
15 Address Space Ownership % whois -h whois.arin.net[Querying whois.arin.net][whois.arin.net]OrgName: Georgia Institute of TechnologyOrgID: GITAddress: Fourth St NWAddress: Rich BuildingCity: AtlantaStateProv: GAPostalCode: 30332Country: USNetRange:CIDR: /16NetName: GITNetHandle: NETParent: NETNetType: Direct AssignmentNameServer: TROLL-GW.GATECH.EDUNameServer: GATECH.EDUComment:RegDate:Updated:RTechHandle: ZG19-ARINRTechName: Georgia Institute of TechnologyNetwork ServicesRTechPhone:RTechOrgTechHandle: NETWO653-ARINOrgTechName: Network OperationsOrgTechPhone:- Regional Internet Registries (“RIRs”)- Public record of address allocations- ISPs should update when delegating address space- Often out-of-date
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