Networks. an overview. dr. C. P. J. Koymans. Informatics Institute University of Amsterdam. February 4, 2008

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1 Networks an overview dr. C. P. J. Koymans Informatics Institute University of Amsterdam February 4, 2008 dr. C. P. J. Koymans (UvA) Networks February 4, / 53

2 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

3 Outline Network modeling 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

4 Outline Network modeling Layered networks 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

5 Network modeling Layered networks OSI model Obligatory 7-layer view, in particular for TCP/IP Link layer (2): switching mostly connectionless (Ethernet) Network layer (3): routing connectionless (IP) Transport layer (4) connection-oriented on layer 4 (TCP) also connectionless on layer 4 (UDP) dr. C. P. J. Koymans (UvA) Networks February 4, / 53

6 Network modeling Layered networks Interfaces and Protocols Interfaces Same computer Different layer Vertical: SDU (Service Data Unit) via SAP (Service Access Point) to/from lower layer Protocols Different computer Same layer Horizontal: PDU (Protocol Data Unit) to/from peer mostly through a lower layer dr. C. P. J. Koymans (UvA) Networks February 4, / 53

7 4 Interfaces and Protocols illustration Layer N+1 PDU Layer N+1 SDU +Control -Control SDU Layer N PDU Layer N

8 Network modeling Layered networks Headers Layer N adds control (header/trailer/...) to Layer N+1 Encapsulation Multiplexing Demultiplexing Decapsulation dr. C. P. J. Koymans (UvA) Networks February 4, / 53

9 5 PDU encapsulation and multiplexing Headers Layer N adds control (header/trailer/...) to Layer N+1 Encapsulation Multiplexing Demultiplexing Decapsulation PDU n = Control PDU n+1 =SDU n

10 Outline Network modeling Networks as graphs 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

11 6 Host Pictures (1) Host

12 7 Two hosts and a network Pictures (2) Host Network Host

13 8 Two hosts, two networks and a router Pictures (3) Host Network Router Network Host

14 Networks with a WAN-connection The Internet Pictures (4) Host Network Router Network Host WAN Link Host Network Router Network Host The Internet 9

15 Outline Network modeling Addressing in graphs 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

16 Network modeling Addressing in graphs Addresses Missing in the pictures are some fundamental concepts Addresses Locators Used in routing Explicit network elements As nodes Not as edges dr. C. P. J. Koymans (UvA) Networks February 4, / 53

17 11 Host with interface Pictures (1bis) Host Host has an interface Interface has an address

18 12 Network as a node Pictures (2bis) Host Network Host Host Network Host

19 13 Router has multiple interfaces Picture (3bis) Host Network Router Network Host

20 14 Duality of nodes and networks Bipartite Graphs Nodes Interfaces Networks

21 15 Abstraction of layers Refinement H H Layer 3 Layer 3 N H Layer 2 N Layer 2 B H Layer 2 N Layer 2

22 Outline Routing 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

23 Outline Routing Basic Routing 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

24 Routing Basic Routing Basic routing Delivering packets to an address Using a number of hops through intermediate networks (using wires, air, devices,... ) Can be done at all layers, not only the network layer Based on table lookup of next hop dr. C. P. J. Koymans (UvA) Networks February 4, / 53

25 Outline Routing Locations and Endpoints 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

26 Routing Locations and Endpoints Locations versus endpoints Addresses are the locators for locations They are the names for the locations Names for endpoints are missing Hosts, processes, communication endpoints Is this an architectural flaw? dr. C. P. J. Koymans (UvA) Networks February 4, / 53

27 Routing Locations and Endpoints Overloading of A records in DNS Host with multiple interfaces... Overloaded A records router.students.os3.nl. A router.studlab.os3.nl. A router.os3.nl. A A Corresponding PTR records in-addr.arpa. PTR router.students.os3.nl in-addr.arpa. PTR router.studlab.os3.nl. dr. C. P. J. Koymans (UvA) Networks February 4, / 53

28 Outline Routing IP addressing 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

29 Routing IP addressing IP (layer 3) addresses IP version 4 32 bit addresses Network part (first), host part (last) Decimal dotted notation dr. C. P. J. Koymans (UvA) Networks February 4, / 53

30 Routing IP addressing Address classes Definition An IP address is a function f : 32 2(= {0, 1}) Class A: f (0) = 0; f (0),..., f (7) network part Class B: f (0) = 1; f (1) = 0, f (0),..., f (15) network part Class C: f (0) = f (1) = 1; f (2) = 0, f (0),..., f (23) network part Class D: f (0) = f (1) = f (2) = 1; f (3) = 0 multicast Class E: f (0) = f (1) = f (2) = f (3) = 1 reserved dr. C. P. J. Koymans (UvA) Networks February 4, / 53

31 Routing IP addressing Special addresses Definition (Special addresses) IP address unknown loopback address (anycast?) Host part all 0 Network identification Host part all 1 Directed broadcast Local broadcast dr. C. P. J. Koymans (UvA) Networks February 4, / 53

32 Routing IP addressing Private addresses Definition (Private addresses) Class Address Range # of nets CIDR notation A /8 B /12 C /16 B /16 (Link local dynamic configuration) dr. C. P. J. Koymans (UvA) Networks February 4, / 53

33 Intermezzo The Routing Tree λ and so on

34 Outline Routing Subnetting 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

35 Routing Subnetting Subnetting Original RFC 950 subnetting Only one level of subnets All subnets are the same size (RIPv1 friendly) Subnets all-zeroes and all-ones are not allowed This has been obsoleted in the all-cidr era Example subnet scheme Divide the class B net /16 into 254 class C nets /24,..., /24 dr. C. P. J. Koymans (UvA) Networks February 4, / 53

36 Routing Subnetting Masks Not necessarily contiguous according to RFC 950 Silly subnetting example Netmask (in a class C scenario) 88 = (explain... ) subnets with 30 (explain... ) hosts each This is really obsolete, because humans can t handle it well Nowadays masks are contiguous (33 options) And all-zeroes and all-ones subnets are allowed dr. C. P. J. Koymans (UvA) Networks February 4, / 53

37 Routing Subnetting Possible Masks Definition (Possible masks) Prefix length Subnet mask CIDR notation (for first non-zero net) / / / / /32 dr. C. P. J. Koymans (UvA) Networks February 4, / 53

38 Routing Subnetting Variable Length Subnet Masks Definition (VLSM) Variable length subnet masks (VLSM) is the idea to use subnets that are not necessarily all the same size. Not possible with RIPv1 Subnets can be subnetted again, and again, and again Used to organize and subdivide larger organizations (universities, enterprises) dr. C. P. J. Koymans (UvA) Networks February 4, / 53

39 Routing Subnetting network and subnetwork disappears. dr. C. P. J. Koymans (UvA) Networks February 4, / 53 CIDR Definition (CIDR) Classless Inter-Domain Routing (CIDR) is the idea to put the division between network part and host part of addresses on arbitrary bit positions, not only on 8, 16 or 24 bit positions as in classful A/B/C-networks. This idea comes from the need for supernetting It is also used to aggregate routes Routing is based on longest match (which is most specific) A-, B-, C-classes are abandoned Together with VLSM, the difference between

40 Routing Subnetting Point to Point links Usually the interface at both ends each have an IP address Often a /30 is used for that Point to Point links may be unnumbered Or may use a /31 (RFC 3021) Or may use two /32 s (within PPP, RFC 1332) dr. C. P. J. Koymans (UvA) Networks February 4, / 53

41 Outline Routing IPv6 addressing 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

42 Routing IPv6 addressing IPv6 addresses IP version bit addresses 4 times as many bits as IPv times as many addresses Much more hierarchical addressing See also the IPv6_intro presentation dr. C. P. J. Koymans (UvA) Networks February 4, / 53

43 Outline Packet formats 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

44 Outline Packet formats IPv4 packets 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

45 IPv4 header Version IHL Type of Service Total Length Identification Flags Fragment offset Time to Live Protocol Header Checksum Source IP Destination IP Options (optional; padded)

46 Packet formats IPv4 packets IPv4 header fields IPv4 header fields Version 4 IHL Total header length in 32-bit words (5-15) Type of Service Now used for DiffServ and ECN Total Length Including header, in bytes (max 65535) Identification Used with fragmentation Flags DF (Don t Fragment) and MF (More Fragments) Fragment offset First packet has offset 0 dr. C. P. J. Koymans (UvA) Networks February 4, / 53

47 Packet formats IPv4 packets IPv4 header fields (continued) IPv4 header fields (continued) Time to Live Really a hop count Protocol Upper layer protocol differentiation Header Checksum One s complement of one s complement sum Source Address IP address of sender Destination Address IP address of receiver Options Source routing, timestamp,... dr. C. P. J. Koymans (UvA) Networks February 4, / 53

48 Packet formats IPv4 packets Protocol Common protocols 1 ICMP 2 IGMP 4 IP in IP 6 TCP 17 UDP Less common protocols 41 IPv6 in IP 47 GRE 89 OSPF 111 IPX in IP 115 L2TP dr. C. P. J. Koymans (UvA) Networks February 4, / 53

49 Outline Packet formats IPv6 packets 1 Network modeling Layered networks Networks as graphs Addressing in graphs 2 Routing Basic Routing Locations and Endpoints IP addressing Subnetting IPv6 addressing 3 Packet formats IPv4 packets IPv6 packets dr. C. P. J. Koymans (UvA) Networks February 4, / 53

50 Packet formats IPv6 packets IPv6 header Vers. Traffic Class Flow Label Payload Length Next Header Hop Limit Source Address Destination Address dr. C. P. J. Koymans (UvA) Networks February 4, / 53

51 Packet formats IPv6 packets IPv6 header fields IPv6 header fields Version 6 Traffic Class Flow Label Payload Length Next Header Hop Limit Source Address Destination Address Type of Service management Identify flows with special requirements Including extension headers Type of following header Forwarding count and loop protection IPv6 address of sender IPv6 address of recipient dr. C. P. J. Koymans (UvA) Networks February 4, / 53

52 Packet formats IPv6 packets Next Header protocol type Header types Number Name Meaning 0 HOPOPT Hop-by-hop Option 6 TCP Upper layer Transmission Control 17 UDP Upper layer User Datagram 41 IPv6 IPv6 (in IPv6) 43 IPv6-Route Routing Header 44 IPv6-Frag Fragment Header dr. C. P. J. Koymans (UvA) Networks February 4, / 53

53 Packet formats IPv6 packets Next Header protocol type Header types (continued) Number Name Meaning 50 ESP Encap Security Payload 51 AH Authentication Header 58 IPv6-ICMP ICMP for IPv6 59 IPv6-NoNxt No Next Header 60 IPv6-Opts Destination Options See dr. C. P. J. Koymans (UvA) Networks February 4, / 53

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