1 / 63

Computer Networks 2

Computer Networks 2. The Network Layer in the Internet. The Network Layer in the Internet. At the Network Layer Internet can be viewed as collection of sub-networks or Autonomous Systems ( ASes ). Properties: There is no real structure,

sspringer
Download Presentation

Computer Networks 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Computer Networks 2 The Network Layer in the Internet Veton Këpuska

  2. The Network Layer in the Internet • At the Network Layer Internet can be viewed as collection of sub-networks or Autonomous Systems (ASes). • Properties: • There is no real structure, • Various Network components held together via a number of Backbones. • High-bandwidth lines, and • Fast Routers • Regional Networks are attached to those backbones. • University LAN’s, Company LAN’s, and Internet Providers are connected to Regional Networks. • A sketch of quasi-hierarchical organization of the Internet is depicted in following figure: Veton Këpuska

  3. The Network Layer in the Internet • The Internet is an interconnected collection of many networks Veton Këpuska

  4. The Network Layer in the Internet • Network Layer Protocol is the glue that holds the whole Internet together. • This protocol is called IP (Internet Protocol). • IP: • Is designed from the beginning with internetworking in mind. Its job is to provide: • A best-effort (i.e., not guaranteed) way to transport datagrams from source to destination. • Connectivity in spite the fact these machines can be on the same network or there are other networks in between them. Veton Këpuska

  5. The Network Layer in the Internet • Communication in the Internet: • The transport layer takes data streams and breaks them up into datagrams. • Datagrams can be up to 64 Kbytes each, but in practice they usually are not more than 1500 bytes (they fit in one Ethernet frame). • Each datagram is transmitted through the Internet, possibly being fragmented into smaller units. • In the destination machine they are reassembled by the network layer into the original datagram. • This datagram is handed over to transport layer. • In the previous sketch an example can be depicted where the packet originating at host 1 has to traverse six networks to get to the destination host 2. Note that in practice it takes much more then six. Veton Këpuska

  6. The IP Protocol • Format of datagrams is a starting point to study the network layer in the internet: • IP datagram consists of: • Header, and • Text part. • Header: • 20-byte fixed part • Variable length optional part. • Header format: Veton Këpuska

  7. The IP Protocol • Transmitted in Big-Endian format: bit order is from left-to-right, with the high order bit of the Version field proceeding the rest. (Note Motorola uses big-endian order while Intel little-endian order). • Conversion is required on all little-endian machines in transmission and reception. • Version field keeps track of which version of the protocol the datagrams are using. • Due to variability of the header size, a field header, IHL, is provided to specify the length of the header in 32 bit (4 bytes) words. • Minimal value of IHL is 5 (no options present) • Maximal value of IHL is 15 (limits the header to 15*4 bytes = 60 bytes => Options field length = 40 bytes). • Note that for some options, for example one that records the route a packet has taken, 40 bytes is not nearly enough, thus making this option useless. Veton Këpuska

  8. The IP Protocol • The Type of Service: • It is intended to specify different classes of service: • Various combinations of reliability and speed are possible. • Examples: • Digitized voice: fast delivery dominates over accurate delivery. • File transfer: error-free transmission is more important then fast transmission. • It is contained in the field of 6 bits: • First three bits (from left to right) specify Precedence filed, and • Three flags: D, T, and R. • Precedence field specifies priority (0-7). • Flag bits allowed the host to specify what requirements are most important ( • Delay, • Throughput, or • Reliability • Theoretically those flags and Precedence level would allow routers to make choices between for example: • Satellite link with high throughput and high delay, and • Leased line with low throughput and low delay. • In practice routers ignore type of service field all together. Veton Këpuska

  9. The IP Protocol • IETF (Internet Engineering Task Force) allowed slight change in the usage/definition of Type of Service field. • Six bits are now used to indicate which of the service classes discussed earlier each packet belongs to. • Total length field includes everything in the datagram: • Header + Data. • Maximum length 216 = 65,535. • Future gigabit networks will require larger datagrams. • Identification field is needed to allow the destination host to determine which datagram a newly arrived fragment belongs to. All fragments of the same datagram contain identical identification field value. Veton Këpuska

  10. The IP Protocol • DF – Don’t Fragment field. It is used to indicate to the router not to fragment the datagram when destination can not put the datagram together from received fragments . • MF – More Fragment field. All fragments with exception to the last one have this bit set. It is used to indicate when the last fragment of a datagram has arrived. • Fragment Offset. Specifies where this fragment belongs in the datagram. All fragments except the last one in a datagram must be a multiple of 8 bytes (elementary fragment unit). • 13 bits => max of 8192 fragments per datagram. • Time to Live. Limits packets lifetime. • It is supposed to count time in seconds, allowing a maximum lifetime of 255 sec. • In practice it just counts hops. When it hits zero the packet is discarded and a warning packet is sent back to the source host. Veton Këpuska

  11. The IP Protocol • Protocol Field: • When Network Layer has assembled a complete datagram it needs to know what to do with it. • This field specifies which transport process to give it to: • TCP (Transmission Control Protocol) • UDP (User Datagram Protocol), etc. • Numbering of protocols is global. Assigned numbers can be located at www.iana.org • Header Checksum. Verifies the header only. • Source Address and Destination Address. Indicate Network Number and Host number (more details later). • Options Field. This field was designated to provide an escape to allow subsequent versions of the protocol to: • Include information not present in the original design, • Allow experimentation with and try outs of new ideas, and • Avoid allocating header bits for the information that is rarely needed. • Option Fields are variable length. Each begins with a: • 1-byte code identifying the option. • Followed by 1-byte option length with some options, and • One or more data bytes. • It is padded to a multiple of four bytes. • Original options are given in the next table. • Current complete and up-to-date list is available at www.iana.org/assignements/ip-parameters Veton Këpuska

  12. The IP Protocol • Some of the IP options: Veton Këpuska

  13. The IP Protocol • Security. • In theory, a military router might sue this field to specify not to route through certain countries the military considers to be “bad guys”. • In practice this field is ignored. • Strict Source Routing. • Gives the complete path from source to destination as a sequence of IP addresses. • The datagram is required to follow that exact route. • Loose Source Routing. • Requires a packet to traverse the list of routers specified, and in the order specified. • It is allowed to pass through other routers on the way. • Useful to avoid certain countries. • Record Route. • Directs routers to append their IP address to the option field. • When the ARPANET was first set up, no packet ever passed through more than nine router, so 40 bytes of option was ample. Now this size is to small. • Timestamp. • Directs routers to also record a 32-bit time stamp. • This option is mostly for debugging. Veton Këpuska

  14. IP Addresses • Every Host and Router on the Internet has an IP address. • IP address encodes device work number and host number. • I principle this combination should be unique; i.e., no two machines on the Internet should have the same IP address. • IP addresses are 32 bits long. • They are used in the Source address and Destination address fields of IP packets. • IP address refers to a network interface and not to a host. • If host is connected to two networks it must have two IP addresses. • IP addresses were divided into five categories (see following figure). Depicted allocation has come to be called Classful Addressing. Note that it is no longer used but there may be numerous reference to it in literature. Veton Këpuska

  15. IP Addresses • IP Address Format Veton Këpuska

  16. IP Addresses • Class A, B, C and D formats allow for up to : • 128 networks with 16 million host each • 16384 networks with up to 64K hosts, or • 2 million networks (e.g., LAN’s) with up to 256 host each. • Class E, that has addresses that begin with 1111 is reserved for future use. • Over 500,000 networks are now connected to the Internet, and the number grows every year. • Network numbers are managed by a nonprofit corporation called ICANN (Internet Corporation for Assigned Names and Numbers) to avoid conflicts. • ICANN has delegated parts of the address space to various regional authorities, which in turn give out IP addresses to ISPs and other companies. Veton Këpuska

  17. IP Addresses • Network addresses are typically written in dotted decimal notation. • In this format each of the 4 bytes is written in decimal from 0 to 255. • Lowest IP address: 0.0.0.0 and highest is 255.255.255.255 • Values 0 and -1 (in signed binary notation, i.e., all 1’s) have special meanings as depicted in the following figure. • 0 means this network or this host. • -1 means all hosts on the indicated network. Veton Këpuska

  18. IP Addresses • IP address 0.0.0.0 is used by hosts when they are being booted. • The IP addresses with 0 as network number refer to the current network. • This convention is used to allow machines to refer to their own network without knowing its number. • However, they have to know its class to know how many 0’s to include. • The address consisting of all 1s allows broadcasting on the local network, typically a LAN. • The addresses with a proper network number and all 1s in the host field allow machines to send broadcast packets to distant LANs anywhere in the Internet. • Note Network administrations can disable this feature. • All addresses of the form 127.xx.yy.zz are reserved for loop back testing. • Packets sent to that address are not put out onto the wire; they are processed locally and treated as incoming packets. Veton Këpuska

  19. Subnets • All host in a network must have the same network number. • This property of IP addressing can cause problems as networks grow. • The problem is the rule that a single class A, B, or C address refers to one network, not to a collection of LANs. • A small change was made to the addressing system to deal with this problem. • Solution: allow a network to be split into several parts for internal use but still act like a single network to the outside world. • Example of a typical University Campus Network: Veton Këpuska

  20. Subnets • A campus network consisting of LANs for various departments. Veton Këpuska

  21. Subnets • In the literature, the parts of the network (in the example before Ethernets) are called subnets. • This definition conflicts with “subnet” to mean the set of all routers and communication lines in a network. • How does the main router know which subnet (Ethernet) to use to deliver a packet? • Maintain a table that associates each host (in the campus) to its corresponding router. • Problems: • Large table (65,536 entries) • Significant amount of manual maintenance in adding, moving, and removing hosts. • Instead of having a single class B address with 14 bits for the network number and 16 bits for the host number, some bits are taken away from the host number to indicate subnet number. • Example: University with 35 departments it could use 6-bit subnet number and a 10 bit host number allowing 26=64 Ethernets each with a maximum of 210-2=1022 hosts. • To implement sub-netting, main router needs a subnet mask. • It indicates the split between network + subnet number and host as shown in the next figure. Veton Këpuska

  22. Subnet Mask • Subnet masks are also written in dotted decimal notation, with the addition of a slash followed by the number of bits in the network + subnet part. In the example bellow subnet mask can be written as: • 255.255.252.0 • Alternate notation is /22 to indicate that the subnet mask is 22 bits long. • A class B network sub-netted into 64 subnets Veton Këpuska

  23. Subnets • Outside the network the sub-netting is not visible, so allocating a new subnet does not require contacting ICANN or changing any external databases. • Following the same example one could use IP addresses for subnet: • 130.50.4.1 • 130.50.8.1 • 130.50.12.1, and so on. • In binary notation: • 10000010 00110010 000001|00 00000001 • 10000010 00110010 000010|00 00000001 • 10000010 00110010 000011|00 00000001 • Note that “|” is used to indicate division of subnet number from host number. 6 bits to the right of | are subnet numbers and 10-bits to the right of | are host numbers. Veton Këpuska

  24. Subnets • Processing of IP packets (by a router). • Each router has a table listing: • Some number of (network, 0) IP addresses, and • Some number of (this-network, host) IP addresses. • First kind contains information on how to get to distant networks • Second kind tells how to get to local hosts. • Associated with each table is the network interface to use to reach the destination. Veton Këpuska

  25. Subnets • When a packet arrives: • Its destination address is looked up in the routing table. • If the packet is for a distant network – packet is forwarded to the next router as specified in the table. • If it is a local host it is sent directly to the destination. • If the network is not present, the packet is forwarded to a default router with more extensive tables. • Each router thus has to keep track of other networks and local hosts and not (network, host) pars, thus reducing the size of the routing table significantly. Veton Këpuska

  26. Subnets • When sub-netting is introduced, the routing tables were changed by introducing entries of the form: • (this-network, subnet, 0), and • (this-network, this-subnet, host). • Router on subnet k knows only how t get to all other subnets and also how to get to all the host on the subnet k. • Thus it does not have to deal with the hosts on the other subnets. That is all that needs to be done is to have each router do a Boolean AN with the network's subnet mask to get rid of the host number and look up the resulting address in its tables. • Example: • packet addressed to: 130.50.15.6 • AND-ed with the subnet mask at the main router with the subnet mask 255.255.252.0/22 to give the address 130.50.12.0 • This address is looked up in the routing tables to find out which output line to use to get to the router for subnet 3. • Subnetting reduces router table space by creating a three-level hierarchy consisting of network, subnet and host. Veton Këpuska

  27. CIDR – Classless InterDomain Routing • IP it is running out of addresses • 1987 – Prediction: Internet might grow to 100,000 networks. • 100,000 network was connected in 1996. • There are over 2 billion of addresses • Organizing them in classes wastes millions of them. • Particular problem is class B network. • Class A network with 16 million addresses is to big for most organizations. • Class C with 256 addresses is too small. • Class B with 65,536 addresses is just right. Veton Këpuska

  28. CIDR • In reality class B is far to large for most organizations (more than half of class B networks have less than 50 hosts). • In retrospect class C network should have been allocated 10 bits (instead of 8 bits) for the host number that would allow 1022 (1024-2: all 0 and -1 special usage addresses) which would give half a million addresses that would have been just right for most organizations instead of 65,536 as is the case for class B. • In 1987 nobody predicted that internet will become a mass market communication system rivaling the telephone network. • On the other hand if 20 bits were allocated to the class B network number, another problem would have emerged: the routing table explosion. • Routers view the IP address space as a two-level hierarchy with network numbers and host numbers. • Routers do not have to know all the hosts but they do have to know all the networks. • If half a million class C networks were in use, every router in the entire Internet would need a table with half a million entries, one per network, telling which line to use to get to that network. • Expensive solution for critical routers that keep the tables in static RAM on I/O boards. • A more serious problem is that complexity of various algorithms relating to management of the tables grows faster than linear. • Finally, the worse problem is that router software and firmware was designed at a time when the Internet had 1000 connected networks and thus design choices made then are far from optimal in current conditions. • Various routing algorithms require each router to transmit its tables periodically (e.g., distance vector protocols). • Larger the tables, greater the likelihood that some parts will get lost. • Loss of data or corrupt data leads to routing instabilities. Veton Këpuska

  29. CIDR • One solution would require to have a deeper hierarchy in routing. • IP address contain a country, state/province, city network address and host field. • Each router would only need to know how to get to each country, the states/provinces in its own country, the cities in that state/province, and the networks in its city. • This solution would require more than 32 bits for IP addresses and would use addresses inefficiently (Liechtenstein would have as many bits as the United States). • Some solutions solve one problem but create the other. Veton Këpuska

  30. CIDR • Basic idea behind Classless InterDomain Routing – CIDR is to allocate the remaining IP addresses in variable sized blocks without regard to CLASSES. • Dropping the classes makes forwarding more complicated. • Original class based algorithm: • 4 bit class number is extracted from the copy of packet IP address. • 16 way branch sorts packets into: A, B, C, and D, E (if supported) class. • A – 8 cases, • B – 4 cases, • C – 2 cases, and • D,E – 1 case. • 8, 16, or 24 bit network number is masked. • The network number is then looked up in the A, B, and C table (typically A and B is indexed while C is hashed) • Corresponding outgoing line form the entry that was found is looked up and used to forward the packet. Veton Këpuska

  31. CIDR • CIDR Algorithm • Single Routing table entry is extended to 32 bits for all networks. • Table consists of array of: • IP address • Subnet mask • Outgoing line, triplet • Destination IP address is extracted. • Matching masked Destination IP address with table entries. • If multiple matches then longest mask is used. Veton Këpuska

  32. CIDR • Commercial Routers use custom VLSI chips with these algorithms embedded in hardware. • Example: • Million of addresses available starting at 194.24.0.0 • Cambridge University needs 2048 addresses => • 194.24.0.0 – 194.24.7.255 • Mask 255.255.248.0 • Oxford University asks for 4096 addresses => • 194.24.16.0 – 124.24.31.255 • Mask 255.255.240.0 • University of Edinburgh asks for 1024 addresses => • 194.24.8.0 – 194.24.11.255 • Mask 255.255.252.0 Veton Këpuska

  33. CIDR - Example Veton Këpuska

  34. CIDR – Example • Routing tables all over the world are now updated with the three assigned entries. Each entry contains a base address and a subnet mask. Entries in binary are: • C: 11000010 00011000 00000000 0000000 11111111 11111111 11111000 0000000 • E: 11000010 00011000 00001000 0000000 11111111 11111111 11111100 0000000 • O: 11000010 00011000 00010000 0000000 11111111 11111111 11110000 0000000 Veton Këpuska

  35. CIDR - Example • Packet addressed to 194.24.17.14 (binary =>) • 11000010 00011000 00010001 00000100 • AND-ed with Cambridge Univ. Mask: • 11000010 00011000 00010000 00000000 • Does not match Cambridge Univ. base address. • AND-ed with Edinburgh Univ. Mask: • 11000010 00011000 00010000 00000000 • Does not match Edinburgh Univ. base address. • AND-ed with Oxford Univ. Mask: • 11000010 00011000 00010000 00000000 • Does match Oxford Univ. base address. Veton Këpuska

  36. CIDR - Example • From a Router in Omaha, Nebraska that has only 4 outgoing lines: • Minneapolis • New York • Dallas • Denver • When Router there gets the three new entries => determines that it can combine all three entries into a single aggregate entry: 194.24.0.0/19 with a binary address and submask as follows: • A: 11000010 00000000 00000000 00000000 • M: 11111111 11111111 11100000 00000000 • This entry will send all packets to New York. In addition aggregation reduces table size. Veton Këpuska

  37. NAT – Network Address Translation • Is way to get around the problem of lack of IP addresses. • ISP with /16 (class B) addresses can accommodate 64k (65,534) hosts. • If ISP has more then 64k customers it can dynamically assign an IP address to a computer when it calls up (dial up connection). • When session is terminated the IP address is reassigned to another user. • This strategy works for home users with dial-up connection but it fails for Broadband (Cable and ADSL) or business users. • Long term solution is migration of IPv6 (128-bit addresses). • Temporary solution NAT – Network Address Translation Veton Këpuska

  38. NAT – Network Address Translation • Basic Idea: • Each Company is assigned a single IP address (or at most small number of them) for internet traffic. • Within the company every computer gets a unique IP address, which is used to route internal traffic. • When packet exits the company to ISP and address translation takes place. • To make this scheme work three ranges of IP addresses have been declared as private. • Internally they can be used as seen appropriate. • The only rule is that no packets containing these addresses may appear on the Internet itself. • Three reserved ranges are: • 10.0.0.0 - 10.255.255.255/8 (16,777,216 hosts) • 172.16.0.0 - 172.31.255.255/12 (1,048,576 hosts) • 192.168.0.0 - 192.168.255.255/16 (65,546 hosts) Veton Këpuska

  39. Sending packets from the network with NAT: NAT box converts internal IP source address (10.0.0.1) to true address (198.60.42.12) NAT box is combined with a firewall. Getting packet from outside world to NAT based network: Source Port Field (designed to be used for TCP or UDP transmissions) can be used to identify the source. Whenever source address is replaced by the company’s IP address by NAT the TCP/UDP source port field is replaced by an index into the NAT box’s 65,536-entry translation table. This table entry contains the original IP address and the original source port. Both the IP and TCP/UDP header checksums are recomputed and inserted into the packet. It is necessary to replace Source Port because connections from two machines (e.g., 10.0.0.1 and 10.0.0.2) may both happen to use the same port (e.g., 5000) so the Source port alone is not enough to identify the sending process. When a packet arrives at the NAT box from the ISP, the Source port in the TCP/UDP header is extracted and used as in index into the NAT box’s mapping table. From the located table entry, internal IP address and original TCP Source port are extracted, and inserted into the packet. Checksums are recomputed and inserted into the packet. The packet is then passed to company server for delivery. Placement and operation of NAT box NAT – Network Address Translation Veton Këpuska

  40. NAT – Network Address Translation • The same NAT solution can be applied to Broadband networks (ADSL and Cable). • This solution however, is regarded as breaking fundamental principles of Layered Network Organization: • NAT violates architectural model of IP which states that every IP address uniquely identifies a single machine worldwide. • NAT changes Internet from a connectionless network to a kind of connection-oriented network. • NAT box must maintain information (mapping) for each connection passing through it. Having the network maintain connection sate is a property of connection-oriented network. • If NAT box crashes and its mapping table is lost, all its TCP connections are destroyed. In the absence of NAT router crashes have no real effect on the network. (The sending process times out and resends all unacknowledged packets). • With NAT the Internet becomes as vulnerable as a circuit-switched network. • NAT violates the most fundamental rule of protocol layering: layer k may not make any assumptions about what layer k+1 has put into the payload field. This principle is there to keep layers independent. If TCP is later upgraded to TCP-2 with different header layout NAT will fail. The idea of independence of layers is to ensure that changes in one layer do not affect other layers. NAT destroys this independence. • Processes on the Internet are not required to use TCP or UDP. If a user on machine A decides to use a new transport protocol to communicate with a user on the machine B, introduction of NAT box will cause this application to fail because NAT will not be able to locate TCP Source Port correctly. • Some applications insert IP addresses in the body of the text like FTP (File Transfer Protocol) or Internet Telephony. The receiver extracts these addresses and uses them. However, since NAT does not know about these addresses it cannot replace them, so any attempt to sue them on the remote side will fail. It may be possible to patch NAT every time a new application or standard comes along (e.g., like H.323 for Internet telephony) but doing this for every new application comes along is not a good idea. • Since TCP Source port field has only 16-bits it can only be used for up to 64k machines. • Finally by introducing NAT, (a hack) that temporarily fixes the problem of lack of IP addresses, it only delays implementation of the real solution and transition of IPv6, and this is a bad think. Veton Këpuska

  41. Internet Control Protocols • It serves to monitor closely the operation of the Internet. • Internet Control Message Protocol (ICMP) • Address Resolution Protocol (ARP) • Reverse Address Resolution Protocol (RARP) • Bootstrap Protocol (BOOTP) • Dynamic Host Configuration Protocol (DHCP). Veton Këpuska

  42. ICMP – The Internet Control Message Protocols • Unexpected events are reported by ICMP. • The same protocol is used to test the Internet. • A dozen types of types of ICMP messages are defined more important of which are presented in the table bellow: Veton Këpuska

  43. ARP – The Address Resolution Protocol • Data link layer does not understand IP addresses and thus those can not be used at that level. • LAN Interface hardware uses only LAN addresses. • How does IP address get mapped onto data link layer such as Ethernet? • Answer of this question using following example: Veton Këpuska

  44. ARP – The Address Resolution Protocol • Small University with several class C (now /24) networks • Two Ethernet Networks of • CS (IP: 192.31.65.0) and, • EE (IP: 192.31.63.0) Departments both • Connected to a campus backbone ring (IP: 192.31.60.0) • Each machine on an Ethernet has a unique (48-bit) address labeled E1-E6. • Each machine on the ring has an FDDI (Fiber Distributed Data Interface) ring address labeled F1-F3. Veton Këpuska

  45. ARP – The Address Resolution Protocol • Scenario 1: Host 1 (mary@eagle.cs.uni.edu) sends a packet to a user on Host 2. • Find IP address for host 2 (e.g., eagle.cs.uni.edu) using Domain Name System [DNS] that returns IP address for host 2 (192.31.65.5) • Upper layer software (e.g., application) builds a packet with 192.31.65.5 in the Destination Address field and hands it over to IP software for transmission. • IP software will determine (via a table lookup) that the address of that destination is on its network. • IP software needs to map this IP address to destination’s Ethernet address: • Have a configuration file in the system that maps IP addresses onto Ethernet addresses. (Problem with keeping files up to date; also it is error prone and time consuming operation). Or better solution: • Host 1 broadcast a packet onto the Ethernet requesting information who owns IP address 192.31.65.5. The host 2 responds with its Ethernet address (E2). The protocol used for asking destinations Ethernet address and getting the reply is called ARP (Address Resolution Protocol). • At this point host 1 • Builds Ethernet frame addressed to E2, • Puts the IP packet in the payload field, • Dumps the packet onto Ethernet. • Ethernet board of Host 2 • Detects this frame, • Recognizes it is addressed to itself, • Extracts the IP packet from the payload and passes it to the IP software, • IP software validates that it is correctly addressed and processes it. • Number of optimizations are possible by cashing the information in both host 1 and host2 (e.g., all hosts in the Ethernet network). Veton Këpuska

  46. ARP – The Address Resolution Protocol • Scenario 2: Host 1 sends a packet to a user on Host 4 (192.31.63.8). • Using ARP will fail because host 4 will not see broadcast from host 1. Two solutions: • Proxy ARP: CS router could be configured to respond to ARP request for network 192.31.63.0: • Host 1 will make an ARP cashed entry of (192.31.63.8, E3) and send all traffic for host 4 to local router. • Host 1 immediately determine that the destination is on a remote network and send all such traffic to a default Ethernet address that handles all remote traffic (e.g., in this case E3). • Following Steps are conducted in either case: • Host 1 packs the IP packet into the payload of an Ethernet frame addressed to E3. • CS E3 Router uses this IP address to lookup the next router (192.31.60.7) • If it does not know the FDDI address of that router, it broadcasts an ARP packet onto the ring thus obtaining FDDI address F3 of the router. • Inserts the packet into payload field of an FDDI frame addressed to F3 and puts it on the ring. • EE Router removes that packet from the payload field and delivers it to IP software. • IP software recognized that the packet needs to be send to 192.31.60.7 • If its (192.31.60.7) Ethernet address, E6, is not cashed ARP is used to obtain this information. • Builds the Ethernet frame addressed to Et, Puts the IP packet in the payload field, • Sends the packet over the Ethernet. • Ethernet board of Host 4 • Detects this frame, • Recognizes it is addressed to itself, • Extracts the IP packet from the payload and passes it to the IP software, • IP software validates that it is correctly addressed and processes it. Veton Këpuska

  47. Ethernet to IP Address Mapping • RARP, BOOTP, and DHCP • RARP – Reverse Address Resolution Protocol • Broadcast Ethernet address of a newly-booted device requesting its IP address. • RARP server sends back corresponding IP address. • Disadvantage - RARP protocol uses destination address of all 1s (limited broadcasting) to reach RARP server => an RARP sever is needed on each network. • Alternate Bootstrap Protocol (BOOTP) that unlike RARP uses UDP messages, which are forwarded over routers (i.e., does not require special server). • Problem – BOOTP requires manual configuration of tables mapping IP address to Ethernet address. • DHCP – Dynamic Host Configuration Protocol: • It allows both manual IP address assignment and automatic assignment. • It is based on the idea of a special server that assigns IP addresses to hosts asking for one. • Since DHCP server may not be reachable by broadcasting, a DHCP realy agent is needed on each LAN. Veton Këpuska

  48. IPv6 • New version of IP from current IPv4 that alleviates the problems of this implementation. • In the early years Internet was primarily used by: • Universities, • High-tech Industry, and • Government (DOD). • With the explosion of interest started in mid 1990’s it started to be used by different group of people, especially people with different requirements: • Wireless portables connected to home bases, • Impeding convergence of the computer, communication, and entertainment industries: • Every telephone, • Every TV set, Will become Internet Node, producing a billion machines used for audio and video on demand. • Those circumstances require evolution current IPv4 to a more flexible IP standard. Veton Këpuska

  49. IPv6 • IETF in 1990 started work on a new version of IP. Its major goals were: • Support billions of hosts, even with inefficient address space allocation. • Reduce the size of the routing tables. • Simplify the protocol, to allow routers to process packets faster. • Provide better security (authentication and privacy) than current IP. • Pay more attention to type of service, particularly for real-time data. • Aid multicasting by allowing scopes to be specified. • Make it possible for a host to roam without changing its address. • Allow the protocol to evolve in the future. • Permit the old and new protocols to coexist for years. Veton Këpuska

  50. IPv6 • IPv6 adopted from Deering and Francis proposals called SIPP (Simple Internet Protocol Plus). • IPv6 is not compatible with IPv4 but it is compatible with other auxiliary Internet protocols: TCP, UDP, ICMP, OSPF, BGP, and DSN. • Major Improvements of IPv6: • Longer Addresses = 16 Bytes long (practically unlimited supply of Internet addresses) • Simplification of the header to 7 fields (from previously 13 in IPv4). • Better support for options. • Big advance in security. • More attention to quality of service. Veton Këpuska

More Related