TCP/IP Basis. OSI Model

Transcription

1 TCP/IP Basis 高 雄 大 學 資 訊 工 程 學 系 嚴 力 行 Source OSI Model Destination Application Presentation Session Transport Network Data-Link Physical ENCAPSULATION DATA SEGMENT PACKET FRAME BITS DECAPSULATION Application Presentation Session Transport Network Data-Link Physical 1

2 TCP/IP Model 涵 蓋 了 OSI 模 型 中 的 Application, Presentation, 和 Session 三 層 TCP 或 UDP IP Socket API LAN, WAN 或 其 它 網 路 Application Layer Examples 2

3 IPv4 Addressing An IP address is a 32-bit sequence of 1s and 0s. To make the IP address easier to use, the address is usually written as four decimal numbers separated by periods. This way of writing the address is called the dotted decimal format. IP Address Structure Network number + Host number Network numbers are assigned by the NIC (Network Information Center) to avoid conflicts. All the hosts in a network ( 可 以 不 透 過 router 而 互 相 通 訊 的 區 域 ) must have the same network number. 3

4 IP Addresses: Self Identification Class Range of host addresses A 0Network Host B 10 Network Host C 110 Network Host D 1110 Multicast address E Reserved for future use to to to to to Classes of IP Network Addresses 4

5 Special IP Addresses All 1s mean all ; All 0s mean this netid Host Network (anything) This host A host on this network Broadcast on the local network Broadcast on a distant network Loopback Host Address vs. Network Address Host address is assigned to a specific interface Network Host Host number cannot be all 0 s Network address refers to a whole network Not assigned to an interface Network Host number is all 0 s For a k-bit host number, total 2 k -2 addresses are assignable (excluding all 0 s and all 1 s) 5

6 One Host Address for One Host? A host can have more than one interfaces Each interface should be configured an independent host address IP Addressing Problems 32-bit IP address space is not enough Organizing the address space by classes wastes millions of them a class B address is far too large for most organizations the routing table explosion every router in the Internet would need a table with half a million entries, if that much class C networks are in use 6

7 Subnet Addressing ack like a single network to the outside world split into several parts for internal use class B G Subnet Subnet Subnets A Class B Network Host Part IP address Network Subnet Host Subnet mask The standard does not restrict subnet masks to select contiguous bits of the address. 7

8 Introduction to Subnetting Host bits must are reassigned (or borrowed ) as network bits. The starting point is always the leftmost host bit. 5 bits borrowed allows or 30 subnets (sn 全 為 0 或 1 的 無 法 使 用 ) Determining Subnet Mask Size Class C address with a subnet mask of (3 bits borrowed) Network Field SN Host Field The address would be on the subnet

9 Establishing the Subnet Mask Address Determines which part of an IP address is the network field and which part is the host field. Follow these steps to determine the subnet mask: 1. Express the subnetwork IP address in binary form. 2. Replace the network and subnet portion of the address with all 1s. 3. Replace the host portion of the address with all 0s. 4. Convert the binary expression back to dotteddecimal notation. Subnet Mask Subnet mask in decimal = = IP address / 20 9

10 Network Growth Problem Problem Immense administrative overhead Every time a new network is installed the system administrator has to contact NIC to get a new network number. Then this number must be announced worldwide. Large routing table Solution: To minimize network numbers by sharing one network number among multiple physical networks Classless InterDomain Routing (CIDR) To solve the IP address depletion problem and the routing table explosion problem RFC 1519 The basic idea behind CIDR is to allocate the remaining class C networks in variable-sized (2 x ) blocks 10

11 Example X University needs 2048 addresses and is assigned the addresses through , along with mask Y University needs 4096 addresses and is assigned the addresses through , along with mask Z University needs 1024 addresses and is assigned the addresses through , along with mask Example 28 Class C networks Routing table with entries base address mask =( ) 2 240=( ) 2 252=( ) 2 Destination address with =( ) 2 Dest. IP & mask & = & = match & =

12 Classless InterDomain Routing (CIDR) The world was partitioned into zones, each given a portion of the class C address space: Addresses to for Europe Addresses to for Others Addresses to for North America Addresses to for Central and South America Addresses to for Asia and Pacific Addresses to for Others Addresses to reserved for future use Internet Addressing: Host Names Mnemonic address made up of two parts: Domain name Assigned by a registrar Example: aw.com Top level domain: Classification of domain owner By usage Example:.com = commercial By country Example:.au = Australia Subdomains and individual host names Assigned by domain owner Example: r2d2.compsci.nowhereu.edu Translation between mnemonic addresses and IP addresses handled by name servers (DNS server) 12

13 Public and Private IP Addresses No two interfaces that connect to a public network can have the same IP address because public IP addresses are global and standardized. However, private networks that are not connected to the Internet may use any host addresses, as long as each host within the private network is unique. Private Addresses and NAT three blocks of IP addresses are set aside for private, internal use. Class A B Private Address Range to to C to Connecting a network using private addresses to the Internet requires translation of the private addresses to public addresses using Network Address Translation (NAT). 13

14 NAT Translation Example NAT Router Src = Dst. = Src = Dst. = Internet Private Network Src. = Dst. = NAT Router Src. = Dst = Internet Dynamic Host Configuration Protocol (DHCP) DHCP allows a host to obtain an IP address (public or private) using a defined range of IP addresses on a DHCP server. As hosts come online, contact the DHCP server, and request an address. 14

15 DHCP 與 NAT 在 家 庭 網 路 的 使 用 Private Network PC1 取 得 IP address 的 方 式 與 Router 相 同 PC1 PC2 Switch Router ADSL Modem To the Internet PC Router 透 過 PPPoE 建 立 與 ISP 的 link layer 並 取 得 public IP address 2. Router 啟 動 DHCP 與 NAT 服 務 3. PC3 使 用 DHCP 取 得 private IP address IP 分 享 器 Private Network Switch Router ADSL Modem To the Internet + DHCP + NAT IP 分 享 器 15

16 無 線 IP 分 享 器 Private Network Switch Router Modem To the Internet AP + DHCP + NAT 無 線 IP 分 享 器 Transmission Control Protocol (TCP) The protocols that use TCP include: FTP (File Transfer Protocol) HTTP (Hypertext Transfer Protocol) SMTP (Simple Mail Transfer Protocol) Telnet 16

17 UDP The protocols that use UDP include: TFTP (Trivial File Transfer Protocol) SNMP (Simple Network Management Protocol) DHCP (Dynamic Host Control Protocol) DNS (Domain Name System) TCP and UDP Port Numbers Both TCP and UDP use port (socket) numbers to pass information to the upper layers. Numbers below 1024 are considered well-known ports numbers. Numbers above 1024 are dynamically assigned ports numbers. Registered port numbers are those registered for vendor-specific applications. Most of these are above

18 Some Well-Known Port Numbers IPv6: Introduction The main problem of IPv4 is its relatively small address space IPv6 extends IP address to 128 bits 18

19 IPv6 Address Hexadecimal Notation Similar to IEEE 802 MAC addresses Colon hexadecimal notation 805B:2D9D:DC28:0:0:FC57:D4C8:1FFF Zero compression Contiguous zeros are replaced by doubled colons (can appear only once) 805B:2D9D:DC28::FC57:D4C8:1FFF Two zero words here IPv6 Mixed Notation IPv4 address can be embedded in an IPv6 address It is useful to show the IPv4 portion of the address in dotted-decimal format 805B:2D9D:DC28::FC57: :0:0:0:0:0: becomes ::

20 IPv6/IPv4 Address Embedding IPv4-compatible IPv6 addresses Special address assigned to IPv6-capable devices 32-Bit IPv4 Address Used only for devices that are actually IPv6-aware 便 於 轉 換 成 IPv4 位 址 Prefix IPv4 Address With 80 Zero Bit IPv6 Address In Mixed Notation Compressed IPv6 Address :: IPv6/IPv4 Address Embedding IPv4-mapped IPv6 addresses Regular IPv4 addresses that have been mapped into IPv6 address space 32-Bit IPv4 Address For devices that are not IPv6-capable 由 IPv4 位 址 轉 換 來 的 Prefix IPv4 Address With 64 Zero Bit and 14 One Bit IPv6 Address In Mixed Notation Compressed IPv6 Address FFFF ::FFFF:

21 IPv6 Address Prefix Length Representation IPv6 addresses are divided into a number of network ID bits followed by a number of host ID bits The network identifier is called the prefix, and the number of bits used is prefix length The prefix is represented by adding a slash after the address and then putting the prefix length after the slash 805B:2D9D:DC28::FC57:D4C8:1FFF / 48 21