Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 521Host Naming15-441, Computer NetworksMarch 20, 2006Dave Eckhardtsome slides from Dave Maltz1Overview●Three names for your PC–Why?●Two “resolution” protocols–DNS, ARP●Turning on–DHCP1Three names for your my PC●PIPER.NECTAR.CS.CMU.EDU–What's a “nectar”?–What's a “piper”?●128.2.194.80●00-20-AF-D9-FD-CAAll are globally unique–Isn't one globally unique name enough?1Questions about names●Who uses the name?–For what?●Who owns/defines the namespace?●How long is the name valid?1PIPER.NECTAR.CS.CMU.EDU●Who?–Human beings●What?–Remembering a name for each box–Crude service-location mechanism●www.<organization>–Crude device-location registry●dsl093-172-001.pit1.dsl.speakeasy.net●110.ge-0-0-0.cr1.wdc1.speakeasy.net1Fun break – hostname schemes●Animals, birds, dinosaurs●Cars, wines●CMU SCS Facilities–Desktop machines: astronomical entities–Servers: fruits, nuts, vegetables●NECTAR Project: self-destructive celebrities●Wean cluster: medication●MIT AI Lab: Breakfast cereals1PIPER.NECTAR.CS.CMU.EDU●Who owns the namespace?–Broadly, CMU School of Computer Science (see below)●How long is it valid?–Lifetime of “the machine”●What does it “mean” (bind to?)–How long is the binding valid?●See below1128.2.194.80●Who/what pairs–Who=IP router, usage=...–Who=end-system hosts, usage=1IP Routers●Usage=“Which link does the packet leave on?”–“Definition” of IP router:●Box computing “IP address departure link”–Used as table lookup key●Addresses should be short, mostly fixed length●String would not do–IP address structure●“Network ID”: top bits●“Host ID”: bottom bits●Network/host division depends on frame of reference1IP routers●Usage=Link parameters (some optional)–IP address link/station address (ARP, see below)–IP address link-level encryption state (802.11)–IP address link-level scheduling policy (rare today)–Again, IP address is table-lookup key1End-system hosts●Usage=connection management–TCP connection defined by (IP1, port1, IP2, port2)●“only” 65536 TCP connections per host pair–Client: my ____ server is x.y.z.w–IPsec security layer: IP address security state●For end-to-end security, independent of link-level security●Usage=access control–Trust certain IP addresses more than others●Very weak “security”; you must add something more1128.2.194.80●Who owns the namespace?–Roughly, CMU School of Computer Science●How long is it valid?–Historically: “a long time”●128.2 = CMU.EDU●194 = some chunk of CS●80 = random selection●No need to change for “lifetime of machine”–But...1128.2.194.80●Nothing fails like success–Internet popularity IP router table size explosion●CIDR compresses via hierarchy–12.0.0.0/8 (12.*) belongs to ATT.net–216.218.128.0/17 belongs to he.net (Hurricane Electric)–216.218.132.24/29 belongs to Panasas.com●Change ISPs, your netblock changes–... “ISP” can be Starbucks 802.111128.2.194.80●Who owns the namespace?–Your ISP, probably●How long is the name good for?–At least a couple of minutes100-20-AF-D9-FD-CA●Who assigns?–IEEE http://standards.ieee.org/regauth/oui/–00-20-AF assigned to 3Com–D9-FD-CA assigned by factory1IEEE 802 MAC address●Globally unique address●For every “Ethernet” “card”●“Ethernet”–Or 802.11, or ATM, or Frame Relay, or ...●“card”–Semi-permanent expansion card–PCMCIA/CompactFlash card–Chip on motherboard1IEEE 802 MAC address - Usage●“Station” identification on “a network”●Cooperating set of bridges agree on location–Which bridge owns which stations–Dynamic “spanning tree” algorithm●Not “routable” outside that network–If somebody steals my laptop, knowing the Ethernet address does not generally help me find the laptop.–Then why is it globally unique?1Must IP routers know MAC addresses?●Why do we need a MAC address?–Can't IP-layer entity ignore link-level addresses?●IP was designed to be subnet-independent–ARPAnet, SATnet, ARPA mobile radio network–DIX Ethernet, IBM Token Ring, Corvus Omninet, PPP–Each link has its own kind of address●Differ in size, meaning●“In theory” IP forwarding is “about” IP addresses, doesn't involve link addresses1Must IP routers know MAC addresses?●Link layers are designed to be network-independent●It is a feature that Ethernet can carry–PUP, IP, XNS, Banyan Vines, DECnet, SNA–Each network layer has its own kind of address●Differ in size, meaning●Link layers use MAC addresses for efficiency–Each station can ignore not-for-it traffic in hardware●“In theory” MAC frames can contain any IP address–or none!1Which Addresses Are In The Packet?PLNTA00:FE:F31.1.1.8GRACKLEPLNTA00:FE:F47.7.7.8VORTEXPLN98:FE:221.1.1.1WHIZ98:FE:237.7.7.1????1Frame MAC AddressesPLNTA00:FE:F31.1.1.8GRACKLEPLNTA00:FE:F47.7.7.8VORTEXPLN98:FE:221.1.1.1WHIZ98:FE:237.7.7.198:FE:23 00:FE:F41Packet IP AddressesPLNTA00:FE:F31.1.1.8GRACKLEPLNTA00:FE:F47.7.7.8VORTEXPLN98:FE:221.1.1.1WHIZ98:FE:237.7.7.11.1.1.8 7.7.7.81Address “Mismatch”PLNTA00:FE:F31.1.1.8GRACKLEPLNTA00:FE:F47.7.7.8VORTEXPLN98:FE:221.1.1.1WHIZ98:FE:237.7.7.1MAC: WHIZ VORTEX IP: GRACKLE VORTEX1Must IP routers know MAC addresses?●Result: router-level entities must know MAC addresses●To forward toward destination–Know MAC address of next-hop router●To deliver to final destination–Know MAC address of end-system host1Three names for my PC●PIPER.NECTAR.CS.CMU.EDU–For human use–Good for “a long time”–Maps to IP address for IP routers efficiency●128.2.194.80–For use by IP routers and IP protocols–Good while attached via a given ISP–Mapped to link-level address for link-level efficiency●(not point-to-point links)1Three names for my PC●00-20-AF-D9-FD-CA–Address used by Ethernet link hardware–Good for lifetime of interface card–Binding to machine is variable●Motherboard: pretty permanent●PCI card: rarely
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