Internet Addressing and NamingToday: Addressing and NamingBootstrapping: Networks of InterfacesARP: IP Addresses to MAC addressesInterconnecting LANs: BridgingLearning BridgesVirtual LANs (VLANs)IPv4 Addresses: Networks of NetworksPre-1994: Classful AddressingProblem: Routing Table GrowthRouting Table Growth: Who Cares?Possible SolutionsClassless Interdomain Routing (CIDR)Benefits of CIDRForwarding: Longest Prefix Match1994-1998: Linear GrowthAround 2000: Fast Growth ResumesFast growth resumesMultihoming Can Stymie AggregationHacky Hack: LPM to Control TrafficThe Address Allocation Process/8 Allocations from IANAAddress Space OwnershipDo Prefixes Reflect Topology?Two ProblemsCase #1: Coarse-Grained PrefixesCase #2: Fine-Grained PrefixesTake-home lessonsIPv6 and Address Space ScarcityIPv6: Claimed BenefitsIPv6: Deployment OptionsIPv6 Deployment StatusIPv6 over IPv4 TunnelsDNS: Mapping Names to AddressesSome Record TypesCachingRoot ZoneSome Recent gTLDsDo you trust the TLD operators?Protecting the Root NameserversDefense: Replication and CachingDNS Hack #1: Reverse LookupDNS Hack #2: Load BalanceDNS Hack #3: Blackhole ListsHighlights from Today’s PaperHighlights and Thought QuestionsInternet Addressing and Naming(Nick Feamster)January 23, 20082Today: Addressing and Naming•Internet Addressing–Step 1: Connecting a single network–Step 2: Connecting networks of networks•IPv4 Addressing–Structure–Scaling problems and CIDR (1994)–Allocation and ownership–Longest prefix match and Traffic Engineering–Issues and design questions–More scaling problems and solutions•Internet Naming–Today: DNS and the naming hierarchy–Research: Flat names•Paper discussion: Jung et al.3Bootstrapping: Networks of Interfaces•LAN/Physical/MAC address–Unique to physical interface (no two alike)–Flat structuresenderframereceiverdatagramframeadapteradapterlink layer protocolWhat are the advantages to separating network layer from MAC layer?•Frames can be sent to a specific MAC address or to the broadcast MAC address4ARP: IP Addresses to MAC addresses•Query is IP address, response is MAC address•Query is sent to LAN’s broadcast MAC address•Each host or router has an ARP table–Checks IP address of query against its IP address–Replies with MAC address if there is a matchPotential problems with this approach?•Caching is key!–Try arp –a to see an ARP table5Interconnecting LANs: Bridging•Receive & broadcast (“hub”)•Learning•Spanning tree (RSTP, MSTP, etc.)6Learning Bridges•Bridge builds mapping of which port to forward packets for a certain MAC addressLAN ALAN BLAN CABC•If has entry, forward on appropriate port•If no entry, flood packetPotential problems with this approach?7Virtual LANs (VLANs)•A single switched LAN can be partitioned into multiple “colors”•Each color behaves as a separate LAN•Better scaling properties–Reduce the scope of broadcast storms–Spanning tree algorithms scale better•Better security properties8IPv4 Addresses: Networks of Networks•32-bit number in “dotted-quad” notation–www.cs.duke.edu --- 152.3.140.510011000 0000001110011000 00000101Network (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–152.3.0.0/16 is a 16-bit prefix with 216 IP addressesTopological Addressing9Pre-1994: Classful AddressingNetwork ID Host ID8 16Class A320Class B10Class C110Multicast AddressesClass D1110Reserved for experimentsClass E111124/8 blocks (e.g., MIT has 18.0.0.0/8)/16 blocks (e.g., Duke has 152.3.0.0/16)/24 blocks (e.g., AT&T Labs has 192.20.225.0/24)Simple Forwarding: Address range specifies network ID length10Problem: 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 horizonSource: Geoff Huston11Routing Table Growth: Who Cares?•On pace to run out of allocations entirely•Memory–Routing tables –Forwarding tables•“Churn”: More prefixes, more updates12Possible Solutions•Get rid of global addresses–NAT•Get more addresses–IPv6•Different aggregation strategy–Classless Interdomain routing13Classless Interdomain Routing (CIDR)IP Address: 65.14.248.0 “Mask”: 255.255.252.001000001 0000111011111000 0000000011111111 1111111111111100 00000000Use two 32-bit numbers to represent a network. Network number = IP address + Mask Example: BellSouth Prefix: 65.14.248.0/22Address no longer specifies network ID range.New forwarding trick: Longest Prefix Match14Benefits 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 1Customer 2AT&T Internet12.20.249.0/2412.20.231.0/2412.0.0.0/815Forwarding: Longest Prefix Match•Forwarding tables in IP routers–Maps each IP prefix to next-hop link(s)•Destination-based forwarding–Each packet has a destination address–Router identifies longest-matching prefix…68.208.0.0/1268.211.0.0/1768.211.128.0/1968.211.160.0/1968.211.192.0/18…68.211.6.120destination addressforwarding tableMore on construction of forwarding tables in next lecture.161994-1998: Linear Growth•About 10,000 new entries per yearSource: Geoff Huston17Around 2000: Fast Growth ResumesClaim: remaining /8s will be exhausted within the next 5-10 years.T. Hain, “A Pragmatic Report on IPv4 Address Space Consumption”, Cisco IPJ, September 200518Fast growth resumesRapid growth in routing tablesDot-Bomb HiccupSignificant contributor: MultihomingSource: Geoff Huston19Multihoming Can Stymie Aggregation•“Stub AS” gets IP address space from one of its providers•One (or both) providers cannot aggregate the prefix12.20.249.0/24AT&T VerizonVerizon does not “own” 12.20.0.0/16. Must advertise the more specific route.Mid-Atlantic Corporate Federal Credit Union (AS 30308)12.20.249.0/2412.20.249.0/2420Hacky Hack: LPM to Control TrafficA10.1.0.0/1710.1.128.0/1710.1.0.0/1610.1.0.0/16BCD10.1.0.0/1710.1.0.0/1610.1.128.0/1710.1.0.0/16Traffic for 10.1.0.0/17Traffic for 10.1.128.0/1721The Address Allocation Process•Allocation policies of RIRs affect pressure on IPv4 address spaceIANAAfriNIC APNIC ARIN LACNIC RIPEhttp://www.iana.org/assignments/ipv4-address-spaceDuke22/8 Allocations from IANA•MIT, Ford, Halliburton, Boeing, Merck•Reclaiming space is