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Network Addressing and Layer 3 internetworking BSAD 141 Dave Novak Sources: Network+ Guide to Networks, Dean 2013.

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Presentation on theme: "Network Addressing and Layer 3 internetworking BSAD 141 Dave Novak Sources: Network+ Guide to Networks, Dean 2013."— Presentation transcript:

1 Network Addressing and Layer 3 internetworking BSAD 141 Dave Novak Sources: Network+ Guide to Networks, Dean 2013

2 Outline Concept of internetworking Why TCP/IP is important The TCP/IP model Intro to IP address IP –vs- MAC Address resolution (revisited) ARP Connectionless service IP datagram Encapsulation

3 Compatibility and Protocols Ensure networking components (hardware and software) work together with respect to networking Compatibility issues on LANs are typically easier to address because a single entity is generally in control of the LAN Same/similar technologies or solutions are implemented

4 Compatibility and Protocols Why is this not necessarily the case off the LAN?

5 Compatibility and Protocols Interface – the logical connection between hardware and software components Physical – hardware to hardware Cables physically connecting serial ports on a device NIC plugging into expansion slot on motherboard Logical – software to software Browser (IE) communicating with OS (Win XP) Application software (Excel) collecting data from large DBMS (Oracle)

6 Compatibility and Protocols Cross between physical and logical – hardware to software (vice versa) Specific OS drivers interfacing with NIC OS kernel interfacing with CPU

7 Compatibility and Protocols Protocol May be proprietary or open May be sanctioned by standards making organizations or market driven

8 Compatibility and Protocols For every interface one or more protocols are generally supported Hardware to hardware Software to software Hardware to software / software to hardware The sum of all protocols employed in a device is typically called the protocol stack

9 Protocol stack VENDORSTACK NovellNetware BanyanVINES AppleAppleTalk Digital Equip CorpDECNET IBMSNA Many vendorsTCP/IP

10 Internetworking Individual proprietary networking technologies designed to fit specific set of constraints Based on vendor preferences Based on different technologies No single technology is best for all needs

11 Motivation for internetworking Internetworking utilizes both hardware and software to provide universal service among heterogeneous networks Universal service

12 Motivation for internetworking Large organization with diverse requirements need may need / use multiple physical networks Different networking technologies may be incompatible because they use different data link protocols Frame formats Addressing schemes Access methods

13 TCP/IP Historically, network protocol stacks designed to work with only one specific (layer 2) network technology or certain types / brands of hardware SNA works with IBM networks / hardware VINES works with Banyan networks TCP/IP designed to work on top of or along with any layer 2 network technology Allow data transfer across heterogeneous networks

14 Achieving universal service TCP/IP stack allows different networks to communicate Different types of hardware Different LAN technologies and frame formats Different addressing schemes Internet protocol stack (TCP/IP) provides the illusion of a single seamless communication system

15 Internetworking concept Hosts perceive a seamless network Functions as though using all same technologies In reality: Many different, unrelated physical networks and technologies

16 Keep in mind Early networks constrained by the requirement of homogeneity TCP/IP creates the illusion that devices are operating on one, big, seamless network In reality, it is not – hundreds of thousands of separate networks using different frame formats and addressing schemes

17 Layering and TCP/IP 7 layer OSI model predates TCP/IP Layer for internetworking protocols does not exist in OSI Fit into the existing model at layer 3 Layer 5, the Session Layer is much less important in the internetworking (TCP/IP) world

18 Layering and TCP/IP TCP and UDP explicitly addresses session management

19 Layering and TCP/IP TCP/IP layering model – Internet layering model or Internet reference model 4 or 5 layers (depending on book) Application Transport Internet Link Layer 4 Layer 3 Layer 2 Layer 1

20 Mapping between OSI and TCP/IP Physical = layer 1 Data link = layer 2 Network = layer 3 Transport = layer 4 Session = layer 5 Presentation = layer 6 Application = layer 7 Application = layer 4 Transport = layer 3 Internet = layer 2 Link = layer 1 OSI ModelTCP/IP Model

21 IP: Internet Protocol An internetwork is a networking abstraction created by software Addresses, packet formats, and delivery techniques independent of physical hardware Keeping layering in mind, how does IP allow communication over heterogeneous networks?

22 Keep in mind Network (software) addresses and MAC (hardware) addresses use different formats Different networking technologies use different MAC (hardware) addresses The specific layer 2 protocols, frame formats, etc. are unique for different physical networks Ethernet MAC address is different from the MAC addresses for token passing hardware

23 Keep in mind Using IP, computers on two completely different physical networks can communicate even though neither physical network is inherently capable of: Translating the MAC address of the other network Recognizing the frame format of the other network How is this done?

24 Encapsulation Wrapping data in a specific protocol header When an IP datagram is encapsulated, the entire datagram is placed into the payload area of a specific frame format

25 IP addressing scheme Unique 32-bit number (version 4) Contains both IP address for source and destination You have to know the IP address of the recipient How do we get the IP address?

26 IP addressing scheme Divided into 2 parts Prefix – indicates the network number Suffix – indicates the specific device Network numbers assigned globally Suffixes can be assigned locally

27 IP Addresses IP addressing - assign high-level protocol addresses to hosts and routers Individual hosts are not responsible for translating remote IP addresses How is a URL converted to IP? How is FQDN converted to IP? How is MAC mapped to IP? How can packet generated on Ethernet LAN be formatted to transmit over T1 link?

28 IP Addresses Routers map between the MAC addresses and IP addresses on the LAN they serve Routers would not necessarily understand other address formats – depends on router configuration IP addresses are abstract addresses created by software EXPLICITLY for routing packets over large heterogeneous networks

29 Routers Basic hardware component used to connect heterogeneous networks Router has: Memory Processor Separate I/O interface for each network to which it connects Network treats router like computer

30 Address resolution Translation or mapping of IP address to MAC address 3 important points about address resolution 1) 2) 3)

31 Address resolution Application on host A sends data to application on host B Application on host A sends data to application on host D RR R R R R BACD

32 Address resolution protocol TCP/IP suite Address Resolution Protocol (ARP) / RARP The protocol responsible for mapping IP – to- MAC and vice versa Reverse ARP (RARP) MAC to IP Ensures devices agree on how to resolve addresses

33 Address –vs- name resolution How is address resolution different from name resolution?

34 How does ARP work? 1) Sending device adds destination IP to packet at Internet layer – becomes an IP datagram 2) Examines ARP table for IP –to- MAC mapping 3) If table has mapping, the destination MAC address is added to the frame header the IP datagram is encapsulated in the frame and the frame is sent 4) If no mapping in table, sending device broadcasts ARP request for destination MAC address 5) If local (same subnet), destination device directly responds 4) 6) If remote (different subnet), default gateway router responds with its MAC address

35 ARP message format There is not a fixed ARP format used for all communication ARP messages are encapsulated in a hardware frame ARP is a protocol in the TCP/IP stack Both ARP and IP messages are dynamic Why is this relevant?

36 Does ARP create a lot of traffic? Software on devices extracts and saves ARP information in temporary memory ARP binding table is managed in cache – temporary storage where old table entries are replaced by newer ones If table runs out of space it begins deleting older entries Stores entries for short period of time: 15 – 30 minutes ARP 1 st searches cache for binding info before using network

37 Does ARP create a lot of traffic? How is this information relevant with respect to the locality of reference principle?

38 ARP and the OSI model Some sources claim ARP resides on layer (2) of the OSI model Others claim ARP resides on layer (3) of the OSI model Best way to think about ARP is that it is a protocol that bridges interface between layers 2 and 3 ARP is the protocol in the TCP/IP stack that is responsible for address resolution

39 ARP and the OSI model ARP forms an important conceptual boundary between physical network interface (layer 2) and higher layers (layers 3 and up) in the OSI model Higher layer protocols and applications use IP address, mapping between IP and MAC is performed at Network Interface ARP hides details of physical addressing, allowing software in higher layers to use the IP address

40 Connectionless service Protocols are only aware of activities, services, and/or functions at the layer they work Specific networking functions are handled at different layers of the OSI Applications and protocols that work at upper layers (5-7) dont know anything about lower layers (1-4) Why is this important and beneficial with respect to application design?

41 Connectionless service TCP/IP stack includes protocols for both connectionless and connection-oriented service Connectionless Connection-oriented

42 Connectionless service Four characteristics of connectionless service: 1) No delay for connection setup 2) Sender doesnt know if packets are successfully delivered 3) Packets can be forwarded independently 4) Overhead is high for each packet

43 Concept of virtual packets Internet communication relies on a hardware-independent packet format known conceptually as a virtual packet Virtual packet = IP datagram in TCP/IP

44 IP datagram Generic, universal packet format that can be used on an internetwork Same general format as hardware frames in terms of having: 1) Header 2) Payload

45 IP datagram Size of IP datagram payload is variable The sending application selects payload of datagram Why is a variable IP datagram payload important in the context of internetworking usage? This is true of Ethernet frames as well

46 IP datagram (IP v4) IP Datagram can contain Min of 1 byte excluding header Max of 64 KB including header IP Datagram header is fixed size (20 bytes) Contains IP address of sender IP address of receiver Frame header contains MAC addresses

47 Best-effort delivery IP datagrams are described as a connectionless, best-effort service The IP makes a best-effort at delivering the packet, but doesnt address: 1) Duplication 2) Out-of-order delivery 3) Corrupt data 4) Packet loss Additional protocols handle these errors

48 Transmission over internet Each physical network may be different. Consequently, the datagram may be encapsulated in different size frames as it travels across the Internet Example: H1 may be an Ethernet frame. H2 may be an FDDI frame. H3 may be a token ring frame

49 Datagram transmission Router prepares datagram for transmission by stripping off any frame associated with the originating LAN Hosts and routers store IP datagram in memory with no additional header When datagram sent across a physical network, it is encapsulated in a frame corresponding to the specific layer 2 technology used on that network Size of frame header (an whether or not a trailer is included) depends on underlying network technology Headers do NOT accumulate – they are discarded after use

50 A transmits to D Token Ring LAN R5 C D Ethernet LAN #1 A B R1 R4 R2 R3 1) A checks ARP table no mapping broadcasts ARP request not local, so R1 responds with its MAC 2) IP datagram at A is encapsulated in Ethernet frame (with R1s MAC address in frame header) frame is sent to R1 3) R1 knows destination (D) is not local examines routing table to determine next hop strips off all frame information related to Ethernet LAN #1 sends IP datagram to next hop 4) Simplified: all routers understand IP address in IP header and eventually the IP datagram is forwarded to edge router R5 5) R5 consults routing table and recognizes that IP address for D is local (on its LAN) 6) Encapsulates IP datagram in token ring frame and puts the frame on the LAN with destination MAC address 7) The frame is passed around the ring when D sees the frame recognizes its MAC address pulls the frame and caches data until it can be processed

51 Summary Concept of internetworking Why TCP/IP is important The TCP/IP model The IP address Address resolution ARP Connectionless service IP datagram Encapsulation


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