Internet

1. Internet Foreleser: Carsten Griwodz Email: griff@ifi.uio.no 1

2. SMTP HTTP FTP TELNET NFS RTP TCP UDP IP + ICMP + ARP WANs LLC & MAC LANs ATM physical MANs Internet Protocol Stackand Some Well-known Protocols Application layer Transport layer Network layer Data link and Physical layer

3. IP Routing 3

4. 40.0.0.7 30.0.0.6 20.0.0.5 20.0.0.6 30.0.0.7 10.0.0.5 To reach hoston network Route to this address Routing table of G 20.0.0.0 Deliver direct 30.0.0.0 Deliver direct 10.0.0.0 20.0.0.5 Network 10.0.0.0 Network 20.0.0.0 40.0.0.0 Network 30.0.0.0 30.0.0.7 Network 40.0.0.0 F G H IP Routing • Routing tables • Routers may have incomplete information • Default paths

5. IP Routing: Historical • Routers: “Core Gateways” • Connect LANs to the backbone, know the routes to all networks • Exchange routing information with each other • Gateway-to-Gateway Protocol (GGP): • Distance vector routing • metric: physical distance • Problems • Today several backbones • Today not all networks are connected directly to the backbone • In GGP all gateways communicate with each other Original implementation ARPANET G1 Gn G2 … Local net n Local net 1 Local net 2

6. IP Routing: Autonomous Systems • Hidden networks Core gateways AS boundary router G1 Autonomous System Local net 1 G2 G3 Local net 4 Local net 2 Local net 3 G4 • Core gateways have to be informed about hidden networks • Autonomous systems (AS)Internet domains • Boundary routers are also called Exterior gateways

7. AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS IP Routing: Autonomous Systems • Many autonomous systems (~70000) • Have different sizes • Exchange services with each other as equals or as provider/customer • Have different relations to each other • Every AS has a unique number • Every AS must know a route to every network

8. IP Routing: Autonomous Systems AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS • Stub domain • One AS, several networks • Networks may have different owners, but in the same AS • Multiconnected domain • Like stub domain • Connected to more than one other AS • No through traffic AS AS AS

9. IP Routing: Autonomous Systems AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS • Peering • Bi-lateral agreement between two directly connected ASes • Exchange routes to all subnetworks • Typically don’t offer global routes to each other • Transit domains • Offer connection service to customer ASes • Offer global routes to customer AS AS AS AS

10. IP Routing: Autonomous Systems AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS • Tier-1 domain • Top level networks • Advertise all global routes • Customer to no-one • No-pay agreements with their peers • Internet Exchange Point • Non-profit organisation • Large centers for interconnecting ASes • Keeps peering costs low for smaller ASes AS AS AS

11. AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS IP Routing: Autonomous Systems • Every AS has a unique number • Every AS must know a route to every network Stub domain Multiconnected domain Peering Internet Exchange Point Tier-1 domains Transit domains

12. IP Routing: Internal and External Routing • Direct Routing/ Interior Protocols: • Both source and destination end systems are located in the same subnetwork • source end system sends datagram to the destination end system • identification done by the local address  mapping • routing is completely defined by the subnetwork routing algorithm N0 N1 N4 N5 N2 N3 • Indirect Routing/Exterior Protocols: • Source and destination end system are located on different networks • source end system sends datagram to the next router • each router determines the next router on the path to the destination end system • routing decision is based only on • the network and subnetwork part of the Internet address, i.e. host part not used

13. IP Routing: Autonomous Systems EGP G1 Autonomous System x Autonomous System 1 Gx Place physically close to each other • ASs are administrative entities • Collects routing information on networks in the AS • Defines boundary routers that transmit routing information to other ASs • Boundary routers will filter routes • Expose information about network reachability to other ASs • May transmit information about other reachable ASs (tier-1 domains, transit domains) • ISP will offer customers access to routes its sees via peerings and transits • ISP will offer peers routes to customers, no routes from transits or other peers

14. AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS AS Exterior Gateway Protocol • Requirements, basic conditions • political • economical • security-related • Requirement examples • to avoid certain autonomous systems • to avoid certain countries • to stay within one country (before going via foreign country) • data of company A should not to pass through company B

15. Border Gateway Protocol (BGP) • Previously: Internet Exterior Gateway Protocol (RFC 1654) • Now: Border Gateway Protocol (RFC 1771, 1772, 1773) is de-facto standard • BGP uses distance path mechanism • Related to distance vector routing • But without count-to-infinity problem • IS sends periodically a list to its neighbours containingestimated distance and preferred Path from itself to each destination for a specified block of reachable IP addresses • Receiving IS evaluates path • Distance • Policy compliance  notion of a path / of how to reach other routers is distributed  but, no criteria for selecting a route is distributed • Each BGP router must have its own criteria, i.e. policy • Remarks • Big updates • But only a limited number of routers

16. Interior Gateway Protocol IGP1 IGPx EGP G1 Autonomous System x Autonomous System 1 Gx IGP1 IGPx • In general: intradomain routing • individual solutions possible • Presently preferred procedures • Routing Information Protocol (RIP): old, retiring • Intermediate System – Intermediate System (IS-IS): long time favorite • Open Shortest Path First (OSPF): scales better than IS-IS • Interior Border Gateway Protocol (iBGP): combined with IS-IS and OSPF

17. Routing Information Protocol (RIP) • Background (regarding the originally used protocol) • developed as a part of Berkeley UNIX • since 1988, RIP Version 1, RFC 1058 • Principle • Distance Vector Routing • Distance in number of hops, 15 is ∞ • Periodic updates: 30 sec cycle, 180 sec with update  ∞ • RIP Version 2 • G. Malkin, RFC 1387, 1388 and 1389 (RIP-MIB) • Uses multicast if necessary to distribute data • Not broadcast • Networks without broadcast or multicast (ISDN, ATM) • “Triggered" updates • To be sent only if the routing table changes

18. OSPF no. Meaning 0 Normal service 2 Minimize financial cost 4 Maximize reliability 8 Maximize throughput 16 Minimize delay Open Shortest Path First (OSPF) • Background: since 1990 Internet Standard, RFCs 1247, 2178 • Transition from DVR to LSR • Principle • Link State Routing • Several possible distance metrics • Metric selection per update packet possible (RFC 1349) • Distribute updates using flooding • Routing tables created using Dijkstra’s "shortest path first" algorithm • Name "Open Shortest Path First“

19. For large autonomous systems AS substructure AS AS backbone area Area Router classes AS boundary routers Backbone routers Area border routers Internal routers To other AS To other AS Open Shortest Path First (OSPF)

20. transform to graph H D E G H B I D E G B I A C F A C LAN F Open Shortest Path First (OSPF) • Adjacency • LSR measures distance to all neighbors • OSPF measures distance to all adjacent nodes • If several routers are connected by a LAN • One is designated router • All other routers on the LAN are adjacent only to it • It is adjacent to all others • Abstraction leads to point-to-point links • Required for Dijkstra’s algorithm

21. Final remarks • IS-IS is similar to OSPF without (working support for) areas • iBGP is often used to distribute tables for routing among ASs inside an AS • Separate the issue from dynamics of IGP • Not all routers inside an AS must carry the full external routing table • Some routers talk iBGP and have the full routing table • Called route reflectors • All route reflectors of an AS must be connected at all times • They have route reflector clients that route all external traffic through them • Multiconnected ASs want to save resources • If two routes to a target AS exist … • … and policies allow it • Hot potato routing

22. Internet Protocol • IP • Defined for the first time in 1981 • J. Postel • RFC 791, September 1981 • Connectionless service • Provide best-efforts service • Without regard to whether • these machines are on the same network • there are other networks in between • Packet length • In theory: up to 64 kBytes • In real life mostly approx. 1500 Bytes

23. Version IPv4: dominant version IPv6: upcoming successor to IPv4 Protocol specific fields IPv4 Datagram Format Internet Network Layers Headers Version 0 Not in use 1 Not in use 2 Not in use 3 Not in use 4 Internet Protocol, version 4 5 Stream Protocol (ST, ST-II) 6 Internet Protocol, version 6 7 IPv77, TP/IX, CATNIP 8 PIP 9 TUBA 10 Not in use 11 Not in use 12 Not in use 13 Not in use 14 Not in use 15 Not in use

24. IPv4 Datagram Format Version IHL Type of service D T R C • 1 bit unused • C (1 bit): low cost • R (1 bit): high reliability • T (1 bit): high throughput • D (1 bit): low delay • OLD definition • Was ignored by routers • Redefined by DiffServ • Precedence (3 bit) • priority 0 (normal) ...7 (network control) • influences the queuing scheme (and not routing)

25. IPv4 Datagram Format • DS Field • Differentiated Services Field • New definition Version IHL DS 0 0 • Class selector codepoints • If of the form xxx000 • Differentiated Services Codepoint • xxxxx0 reserved for standardization • xxxx11 reserved for local use • xxxx01 open for local use, may be standardized later • NEW definition • DiffServ compliant • Not widely deployed yet

26. IPv4 Datagram Format • Protocol type of higher level protocol for transmission • 1 – ICMP Internet Control Message Protocol • 2 – IGMP Internet Group Management Protocol • 3 – GGP Gateway to Gateway Protocol • 4 – IP IP in IP tunneling • 5 – ST ST–II in IP tunneling • 6 – TCP TCP • … Version IHL DS Total length Identification D M Fragment offset Time to live Protocol Header checksum Source address Destination Address

27. IP routers IPv4 Segmentation/Reassembly • Transparent segmentation • Non-transparent segmentation • Used in the Internet

28. IPv4 Segmentation/Reassembly • Total length • Length of the unsegmented datagram in bytes • ≥576 bytes≤65535 bytes • Identification • Unique for all segments of a datagram with same src/dst pair • Flags • DF (1 bit): don’t fragment • MF (1 bit): more fragments • Fragment offset • Offset of this fragment in the datagram in multiples of 8 bytes

29. Options (0 or more) Data IPv4 Datagram Format Version IHL DS Total length Identification D M Fragment offset Time to live Protocol Header checksum Source address Destination Address Padding

30. IP Version 6 Objectives • To support billions of end systems • longer addresses • To reduce routing tables • To simplify protocol processing • simplified header • To increase security • security means integrated • To support real-time data traffic • flow label, traffic class • To provide multicasting • To support mobility (roaming) • To be open for change (future) • extension headers • To coexist with existing protocols Scalability Addressing IPv4 limitations Coexistance

31. Options (0 or more) Source address (128 bit) Destination Address (128 bit) IPv6 vs. IPv4 IPv4 Header Version IHL PRE Type of service ToS Total length Identification D M Fragment offset Time to live Protocol Header checksum Source address (32 bit) Destination Address (32 bit) Version Priority Flow label Payload length Next header Hop Limit IPv6 Header

32. Source address Destination Address IPv6 Header Fields • Priority • differentiation of sources • lower number < lower priority IPv6 Header Version Priority Flow label Payload length Next header Hop Limit With flow control Without flow control 0 Not characterized 8 Continuous rate traffic 1 Filler 9 2 Unattended 10 3 Reserved 11 4 Attended bulk transfer 12 5 Reserved 13 6 Interactive 14 7 Internet management 15

33. Internet Control Message Protocol (ICMP) • History • J. Postel • RFC 792, Sept. 1981 • Purpose • to communicate network layer information • mostly error reportinge.g. in ftp, telnet, http appears "destination network unreachable" • ICMP origin, e.g.: • a router was unable to find the given destination address • router sent back ICMP (Type 3) packet • sending host received the packet, returned error code to TCP • TCP returned error code to application (e.g. ftp, telnet, http) • between hosts, routers (and gateways) • ICMP messages are sent as IP packets • i. e. the first 32 bits of the IP data field are ICMP headers

34. Type Code Checksum Internet Control Message Protocol (ICMP) • Header structure • Type • 16 types, a. o. • destination or port or protocol unreachable • fragmentation necessary but DF (don’t fragment) DF is set • source route failed, redirect (for routing) • echo-request and echo-reply (e.g. for "ping" program) • source quench (packet for congestion control) • Code • states cause if type is "destination unreachable" • e. g. net, host, protocol, port unreachable or • fragmentation needed, source route failed

35. 7 24 A 0 Network Host 14 16 B 1 0 Network Host 21 8 C 1 1 0 Network Host 28 1 1 1 0 Multicast address 28 1 1 1 1 Reserved IPv4 Addresses andInternet Subnetworks • Original global addressing concept for the Internet • For addressing end systems and intermediate systems • each network interface (not end system) has its own unique address • 5 classes

36. IPv4 Address andInternet Subnetworks • Networks grow and should be somehow structured • several networks instead of one preferable • but getting several address areas is hard • since address space is limited • e.g., university may have started with class B address, doesn’t get second one • Problem • class A, B, C refer to one network, not collection of LANs  Allow a network to be split into several parts • for internal use • still look like single network to outside world

37. & & 1 1 1 0 1 0 0 1 0 0 1 0 1 0 0 0 0 1 0 0 1 1 1 1 0 0 1 1 0 0 1 0 0 0 1 0 1 1 1 1 0 0 0 1 0 1 0 0 0 1 0 1 0 0 1 0 0 0 1 0 0 0 1 1 1 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 6 10 IPv4 Address andInternet Subnetworks • Idea • local decision for subdividing host shareinto subnetwork portion and end system portion 14 16 e.g. address 129.8.7.2: 1 0 Network Subnet Host Host To write down subnet addresswith subnet mask use either 129.8.4.0/255.255.252.0 or 129.8.4.0/22 Subnet mask: Subnet address: • Use “subnet mask” to distinguish network and subnet part from host part • Routing with 3 levels of hierarchy • Algorithm in router(by masking bits: AND between address and subnet mask): • packet to another network (yes, then to this router) • packet to local end system (yes, then deliver packet) • packet to other subnetwork (yes, then reroute to appropriate router)

38. CIDR: Classless InterDomain Routing • Subnetting not good enough • Too many organizations require addresses • in principle many addresses due to 32-bit address space • but inefficient allocation due to class-based organization • class A network with 16 million addresses too big for most cases • class C network with 256 addresses is too small • most organizations are interested in class B network, but there are only 16384 (in reality, class B too large for many organizations) • Large number of networks leads to large routing tables  Introduction of CIDR (Classless InterDomain Routing) (RFC1519) • CIDR Principle • to allocate IP addresses in variable-sized blocks • (without regard to classes) • e.g., request for 2000 addresses would lead to • assignment of 2048 address block starting on 2048 byte boundary • but, dropping classes makes forwarding more complicated

39. 194.24.0.0/21 Router 194.24.8.0/22 Router 194.24.0.0/19 Router Unassigned 194.24.12.0/22 194.24.16.0/20 Router CIDR: Classless InterDomain Routing • Search for longest matching prefix • if several entries with different subnet mask length may match • then use the one with the longest mask • i.e., AND operation for address & mask must be done for each table entry • Entries may be aggregated to reduce routing tables

40. IPv6 Addresses Prefix (binary) Usage Fraction 0000 0000 Reserved (including IPv4) 1/256 0000 0001 Unassigned 1/256 0000 001 OSI NSAP address 1/128 0000 010 Novell Netware IPX addresses 1/128 0000 011 Unassigned 1/128 0000 1 Unassigned 1/32 0001 Unassigned 1/16 001 Unassigned 1/8 010 1/8 Provider-based addresses 011 1/8 Unassigned 100 1/8 Geographic-based addresses 101 Unassigned 1/8 110 Unassigned 1/8 1110 Unassigned 1/16 Unassigned 1111 0 1/32 Unassigned 1/64 1111 10 1111 110 Unassigned 1/128 1111 1110 0 Unassigned 1/512 1111 1110 10 Link local use addresses 1/1024 1111 1110 11 Site local use address 1/1024 1111 1111 Multicast 1/256

41. IPv6 Addresses and Anycast • Provider based: approx. 16 mio. companies allocate addresses • Geographically based: allocation as it is today • Link, site-used: address has only local importance (security, Firewall concept) • Should make NAT (network address translation) useless • Anycast definition • previously • unicast, broadcast and multicast • now (new) • anycast • send data to one member of a group • for example to the member which is the nearest one geographically • i.e. a system within a pre-defined group is to be accessed • Anycast application • To search for the nearest web-server • To locate the nearest router of a multicast group • in order to participate in group communication