1、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,Network (16 bits),Host (16 bits),130,207,7,36,Problem: 232 addresses is a lot of table entries So
2、lution: Routing based on network and host 130.207.0.0/16 is a 16-bit prefix with 216 IP addresses,Topological Addressing,Pre-1994: Classful Addressing,Network ID,Host ID,8,16,Class A,32,0,Class B,10,Class C,110,Multicast Addresses,Class D,1110,Reserved for experiments,Class E,1111,24,/8 blocks (e.g.
3、, 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,Problem: Routing Table Growth,Growth rates exceeding advances in hardware and software capabilities Primarily due to
4、Class C space exhaustion Exhaustion of routing table space was on the horizon,Source: Geoff Huston,Routing Table Growth: Who Cares?,On pace to run out of allocations entirelyMemory Routing tables Forwarding tables“Churn”: More prefixes, more updates,Possible Solutions,Get rid of global addresses NAT
5、Get more addresses IPv6Different aggregation strategy Classless Interdomain routing,Classless Interdomain Routing (CIDR),IP Address: 65.14.248.0 “Mask”: 255.255.252.0,Use two 32-bit numbers to represent a network. Network number = IP address + Mask,Example: BellSouth Prefix: 65.14.248.0/22,Address n
6、o longer specifies network ID range. New forwarding trick: Longest Prefix Match,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.
7、20.249.0/24,12.20.231.0/24,12.0.0.0/8,1994-1998: Linear Growth,About 10,000 new entries per year In theory, less instability at the edges (why?),Source: Geoff Huston,Around 2000: Fast Growth Resumes,Claim: remaining /8s will be exhausted within the next 5-10 years.,T. Hain, “A Pragmatic Report on IP
8、v4 Address Space Consumption”, Cisco IPJ, September 2005,Fast growth resumes,Rapid growth in routing tables,Dot-Bomb Hiccup,Significant contributor: Multihoming,Source: Geoff Huston,Multihoming Can Stymie Aggregation,“Stub AS” gets IP address space from one of its providers One (or both) providers c
9、annot 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,The Address Allocation Process,Allocation policies of RIRs affect pressure on IPv4 a
10、ddress space,IANA,AfriNIC,APNIC,ARIN,LACNIC,RIPE,http:/www.iana.org/assignments/ipv4-address-space,Georgia Tech,/8 Allocations from IANA,MIT, Ford, Halliburton, Boeing, Merck Reclaiming space is difficult. A /8 is a bargaining chip!,Address Space Ownership,% whois -h 130.207.7.36 Querying OrgName:
11、 Georgia Institute of Technology OrgID: GIT Address: 258 Fourth St NW Address: Rich Building City: Atlanta StateProv: GA PostalCode: 30332 Country: USNetRange: 130.207.0.0 - 130.207.255.255 CIDR: 130.207.0.0/16 NetName: GIT NetHandle: NET-130-207-0-0-1 Parent: NET-130-0-0-0-0 NetType: Direct Assignm
12、ent NameServer: TROLL-GW.GATECH.EDU NameServer: GATECH.EDU Comment: RegDate: 1988-10-10 Updated: 2000-02-01,RTechHandle: ZG19-ARIN RTechName: Georgia Institute of TechnologyNetwork Services RTechPhone: +1-404-894-5508 RTechEmail: hostmastergatech.eduOrgTechHandle: NETWO653-ARIN OrgTechName: Network
13、Operations OrgTechPhone: +1-404-894-4669,- Regional Internet Registries (“RIRs”) - Public record of address allocations - ISPs should update when delegating address space - Often out-of-date,IPv6 and Address Space Scarcity,128-bit addresses Top 48-bits: Public Routing Topology (PRT) 3 bits for aggre
14、gation 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 bitsPure provider-based addressing Changing ISPs requires renumbering,Header Formats,IPv4,Summary of Fields,Version (4 bits) onl
15、y 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) D
16、estination address (128 bits),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),IPv6 Flows,Traffic can be lab
17、eled with particular flow identifier for which a sender can expect special handling (e.g., different priority level),IPv6: Deployment Options,IPv4 Tunnels Dual-stack Dedicated Links MPLS,Routing Infrastructure,Applications,IPv6-to-IPv4 NAPT Dual-stack servers,IPv6 Deployment Status,Big users: German
18、y (33%), EU (24%), Japan (16%), Australia (16%),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,Transitioning: IPv6
19、over IPv4 Tunnels,http:/ trick for mapping IPv6 addresses: embed the IPv4 address in low bits,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 wont necessa
20、rily 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 dont fully support all IPv6 features in hardware,Another extension: Security (IPSec),Backwards compatible with IPv4 Transport mode
21、: 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,Architectural Discontents,Lack of features End-to-end QoS, host control over routing
22、, end-to-end multicast,Lack of protection and accountability Denial-of-service (DoS)Architecture is brittle,Architectural Brittleness,Hosts are tied to IP addresses Mobility and multi-homing pose problemsServices are tied to hosts A service is more than just one host: replication, migration, composi
23、tionPackets might require processing at intermediaries before reaching destination “Middleboxes” (NATs, firewalls, ),Internet Naming is Host-Centric,Two global namespaces: DNS and IP addressesThese namespaces are host-centric IP addresses: network location of host DNS names: domain of host Both clos
24、ely tied to an underlying structure Motivated by host-centric applications,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 Joes Web page www.berkeley.edu/hippie moves to Web links to his page breakFra
25、gile names constrain movement IP addresses are not stable host names DNS URLs are not stable data names,Solution: Name Services and Hosts Separately,Service identifiers (SIDs) are host-independent data namesEnd-point identifiers (EIDs) are location-independent host namesProtocols bind to names, and
26、resolve them Apps should use SIDs as data handles Transport connections should bind to EIDs,The Naming Layers,User-level descriptors (e.g., search),App session,App-specific search/lookup returns SID,Transport,Resolves SID to EID Opens transport conns,IP,Resolves EID to IP,SIDs and EIDs should be Fla
27、t,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., DHTsFlat names can be used to name anything Once you have a large flat namespace, you never need other global “handles”,Resolution S
28、ervice,Flat Names: Flexible Migration,here is a paper,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) dont break,Domain H,Domain Y,
