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TCP/IP Internetworking: Recap of Single Networks (Subnets)

This chapter provides a recap of single networks (subnets) in TCP/IP internetworking, covering topics such as routers, TCP/IP standards, frames and packets, and major TCP/IP standards.

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TCP/IP Internetworking: Recap of Single Networks (Subnets)

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  1. TCP/IP Internetworking Chapter 8 Updated Dec.2009 XU Zhengchuan Fudan University

  2. Recap • Single Networks (Subnets) • Chapters 4 and 5 covered single LANs • Chapters 6 and 7 covered residential Internet access and single WANs • Internets • Connect multiple single networks using routers • 70%-80% of internet traffic follows TCP/IP standards • These standards are created by the IETF • Chapter 10 looks in more detail at TCP/IP management

  3. Figure 2-8: Hybrid TCP/IP-OSI Architecture Recap TCP/IP standards dominate at the internet and transport layers— transmission across an internet

  4. Figure 2-11: Internet and Transport Layer, Cont. Recap Transport Layer end-to-end (host-to-host) TCP is connection-oriented, reliable UDP is connectionless and unreliable Server Client PC Internet Layer (usually IP) hop-by-hop (host-router or router-router) connectionless, unreliable Router 1 Router 2 Router 3

  5. Frames and Packets Recap • Messages at the data link layer are called frames • Messages at the internet layer are called packets • Within a single network, packets are encapsulated in the data fields of frames Frame Trailer Packet (Data Field) Frame Header

  6. Frames and Packets Recap • In an internet with hosts separated by N networks, there will be: • 2 hosts • One packet (going all the way between hosts) • One route (between the two hosts) • N frames (one in each network)

  7. Figure 2-21: Combining Horizontal and Vertical Communication Recap App Transmission Control Protocol (TCP) Or User Datagram Protocol (UDP) Trans Trans Internet Protocol (IP) Int Int Int Int IP DL Phy Destination Host Source Host Switch 2 Router 1 Switch 3 Router 2 Switch 1

  8. Figure 8-1: Major TCP/IP Standards 5 Application User Applications Supervisory Applications HTTP SMTP Many Others DNS Routing Protocols Many Others 4 Transport TCP UDP 3 Internet IP ICMP MPLS ARP 2 Data Link None: Use OSI Standards 1 Physical None: Use OSI Standards Internetworking is done at the internet and transport layers. There are only a few standards at these layers. We will look at the shaded protocols in this chapter.

  9. Figure 8-1: Major TCP/IP Standards, Continued 5 Application User Applications Supervisory Applications HTTP SMTP Many Others DNS Routing Protocols Many Others 4 Transport TCP UDP 3 Internet IP ICMP ARP 2 Data Link None: Use OSI Standards 1 Physical None: Use OSI Standards At the application layer, there are user applications and supervisory applications. We will look at two TCP/IP application layer supervisory applications in this chapter.

  10. Page 348 • Test Your understanding • 1

  11. IP Addresses 32-Bit Strings Dotted Decimal Notation for Human Reading(e.g., 128.171.17.13)

  12. Figure 8-3: Hierarchical IP Address IP addresses are not simple 32-bit numbers. They usually have 3 parts. Consider the example 128.171.17.13

  13. Hierarchical Addressing • Hierarchical Addressing Brings Simplicity • Phone System • Country code-area code-exchange-subscriber number • 01-808-555-9889 • Long-distance switches near the top of the hierarchy only have to deal with country codes and area codes to set up circuits • Similarly, core Internet routers only have to consider network or network and subnet parts of packets

  14. Router Operation

  15. Figure 8-4: Border Router, Intrernal Router, Networks, and Subnets Border routers connect different Internet networks (In this case, 192.168.x.x and 60.x.x.x). An “x” indicates anything.

  16. Figure 8-4: Border Router, Internal Router, Networks, and Subnets Internal routers connect different subnets in a network. In this case, the three subnets are boxed in red: 192.168.1.x, 192.168.2.x, and 192.168.3.x.

  17. Figure 8-5: Multiprotocol Routing Real routers must handle multiple internet and transport layer architectures— TCP/IP, IPX/SPX, SNA, etc. We will only look at TCP/IP routing

  18. Page 351 • Test Your understanding • 2

  19. Figure 8-6: Ethernet Switching Versus IP Routing Destination address is E5-BB-47-21-D3-56. Ethernet switches are arranged in a hierarchy. So there is only one possible path between hosts. So only one row can match an Ethernet address. Finding this row is very simple and fast. So Ethernet switching is inexpensive per frame handled. One Correct Row

  20. Figure 8-6: Ethernet Switching Versus IP Routing Routing Matches Host 60.3.47.x Because of multiple alternative routes in router meshes, routers may have several rows that match an IP address. Routers must find All matches and then select the BEST ONE. This is slow and therefore expensive compared to switching.

  21. Figure 8-7: The Routing Process • Routing • Processing an individual packet and passing it on its way is called routing • Router ports are called interfaces • Packet arrives in one interface • The router sends the packetout another interface

  22. Figure 8-7: The Routing Process • The Routing Table • Each router has a routing table that it uses to make routing decisions • Routing Table Rows • Each row represents a route for a RANGE of IP addresses—often a network or subnet • All packets with addresses in this range are routed according to that row Route IP Address RangeGoverned by the route Metric Next-Hop Router 1 60.3.x.x 9 B

  23. Figure 8-7: The Routing Process • The Routing Table • Routing Table Columns • Row (route) number: Not in real routing tables • IP address range governed by the row • Metric for the quality of the route • Next-hop router that should get the packet next if the row is selected as the best match Route IP Address Range Metric Next-Hop Router 1 60.3.x.x 9 B 2 128.171.x.x 2 B

  24. Figure 8-7: The Routing Process • A Routing Decision • The router looks at the destination IP address in an arriving packet (in this case, 60.3.47.12). • 1. The router determines which rows match (have an IP address range containing the packet’s destination IP address) • The router must check ALL rows for possible matches Route IP Address Range Metric Next-Hop Router Arriving Packet 60.3.47.12 1 60.3.x.x 9 B Match 2 128.171.x.x 2 B No Match

  25. Figure 8-7: The Routing Process • A Routing Decision • 2. After finding all matches, the router then determines the BEST-MATCH row • 2A. Selects the row with the LONGEST MATCH • 60.3.x.x has 16 bits of match • 60.3.47.x has 24 bits of match so is a better match • 2B. If two or more rows tie for the longest match, router uses the METRIC column value • If cost, lowest metric value is best • If speed, highest metric value is best • Etc.

  26. Figure 8-7: The Routing Process • A Routing Decision • 3. After selecting the best-match row, the router sends the packet on to the next-hop router indicated in the best-match row—Next-Hop Router B in this example. Send Packetout toNHR B Route IP Address Range Metric Next-Hop Router 1 60.3.x.x 9 B Best-Match Row 2 128.171.x.x 2 B

  27. Box A More Detailed Look at Routing Decisions

  28. Figure 8-8: Detailed Row-Matching Algorithm Box • Routing Table Actually, the table does not really have an “IP Address Range” column. Instead, it has two columns to indicate the IP address range: Destination (an IP address) and a mask

  29. Figure 8-8: Detailed Row-Matching Algorithm Box • 1. Basic Rule of Masking • Information Bit 1 0 1 0 • Mask Bit 1 1 0 0 • Result 1 0 0 0 • Where mask bits are one, the result gives the original IP address bits • Where mask bits are zero, the result contains zeros

  30. Figure 8-8: Detailed Row-Matching Algorithm Box • 2. Example • Address (partial) 10101010 11001110 • Mask 11111000 00000000 • Result 10101000 00000000

  31. Figure 8-8: Detailed Row-Matching Algorithm Box • 3. Common 8-bit Segment Values in Dotted Decimal Notation • Segment Decimal Value 00000000 0 11111111 255 • 4. Example • 255.255.255.0 is 24 ones followed by 8 zero • 255.255.255.0 is also called /24 in “prefix notation”

  32. Figure 8-8: Detailed Row-Matching Algorithm Box • Example 1: A Destination IP Address that is in the Range • Destination IP Address of Arriving Packet 10.7.3.47 • Apply the Mask 255.255.255.0 • Result of Masking 10.7.3.0 • Destination Value 10.7.3.0 • Does Destination Value Match the Masking Result? Yes • Conclusion Row 1 is a match.

  33. Figure 8-8: Detailed Row-Matching Algorithm Box • Example 2: A Destination IP Address that is NOT in the Range • Destination IP Address of Arriving Packet 10.7.5.47 • Apply the Mask 255.255.255.0 • Result of Masking 10.7.5.0 • Destination Value 10.7.3.0 • Does Destination Value Match the Masking Result? No • Conclusion Row 1 is NOT a match.

  34. Figure 8-9: Interface and Next-Hop Router Box • Switches • A switch port connects directly to a single computer or another switch • Sending the frame out a port automatically gets it to the correct destination Frame

  35. Figure 8-9: Interface and Next-Hop Router Box • Routers • Router ports (interfaces) connect to subnets, which have multiple hosts and that may have multiple routers • The packet must be forwarded to a specific host or router on that subnet Host IP Packet Host Subnet on Router Interface Next-Hop Router Next-Hop Router

  36. Figure 8-9: Interface and Next-Hop Router Next-Hop Router Box Interface (port) Next-Hop Router Best-match row has both an interface (indicating a subnet) and also a next-hop router value to indicate a host or router on the subnet. (Not just a Next Hop Router Column)

  37. Page 353 • Test Your understanding • 3 • Page 357 • Test Your understanding • 6 • Page 358 • Test Your understanding • 7

  38. The Address Resolution Protocol (ARP)

  39. Figure 8-12: Address Resolution Protocol (ARP) Packet Frame The Situation: The router wishes to pass the packet to the destination host or to a next-hop router. The router knows the destination IP address of the target. The router must learn the target’s MAC layer address in order to be able to send the packet to the target in a frame. The router uses the Address Resolution Protocol (ARP)

  40. Figure 8-12: Address Resolution Protocol (ARP) 1: Router broadcasts ARP Request to all hosts and routers on the subnet.

  41. Figure 8-12: Address Resolution Protocol (ARP) 2: ARP Reply sent by the host with the target IP address. Other hosts ignore it. This is the Destination host

  42. Figure 8-12: Address Resolution Protocol (ARP) 3. Router puts the MAC address in its ARP cache; uses it for subsequent packets to the host

  43. Page 367 • Test Your understanding • 11

  44. Dynamic Routing Protocols Dynamic Routing Protocol Routing Table Information

  45. Figure 8-10: Dynamic Routing Protocols • Routing • How do routers get their routing table information? • Routers constantly exchange routing table information with one another using dynamic routing protocols • Note that the term routing is used in two ways In TCP/IP • For IP packet forwarding and • For the exchange of routing table information through routing protocols Dynamic Routing Protocol Routing Table Information

  46. Page 364 • Test Your understanding • 9

  47. The Domain Name System (DNS)

  48. Figure 8-14: Domain Name System (DNS) Hierarchy A domain is a group of resources under the control of an organization. The domain name system is a general system for managing names. It is a hierarchical naming system. Queries to a DNS server can get Information about a domain.

  49. Figure 8-14: Domain Name System (DNS) Hierarchy The highest level (0) is called the root. There are 13 DNS Root Servers. They point to lower-level servers.

  50. Figure 8-14: Domain Name System (DNS) Hierarchy Top-level domains are generic TLDs (.com, .net., .org, etc.) or country TLDs (.ca, .uk, .ie, etc.)

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