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2001. Hae-Kwang Kim Sejong University

Internet Networking - 1- 2001. Hae-Kwang Kim Sejong University Internet Addresses A 0 7 bits netid 24 bits hostid 0 .0.0.0 to 127 .255.255.255 B 1 0 14 bits netid 16 bits hostid 128 .0.0.0 to 191 .255.255.255 C 1 1 0 21 bits netid 8 bits hostid

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2001. Hae-Kwang Kim Sejong University

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  1. Internet Networking - 1- 2001. Hae-Kwang Kim Sejong University

  2. Internet Addresses A 0 7 bits netid 24 bits hostid 0.0.0.0to 127.255.255.255 B 1 0 14 bits netid 16 bits hostid 128.0.0.0to 191.255.255.255 C 1 1 0 21 bits netid 8 bits hostid 192.0.0.0to 223.255.255.255 D 1 1 1 0 28 bits multicast groupid 224.0.0.0to 239.255.255.255 E 1 1 1 1 28 bits reserved 240.0.0.0to 255.255.255.255

  3. Encapsulation user data Appl. header user data TCP header Application data IP header TCP header Application data Ethernet header IP header TCP header Application data Ethernet tailer

  4. Header info for demultiplexing • 8bit protocol field in IP header • 1: ICMP, 2: IGMP, 6: TCP, 17: UDP • 16bit port number for TCP/UDP header • identify applications • 16bit frame type fled in Ethernet header • identify IP, ARP, RARP

  5. Demultiplexing User process User process User process User process TCP UDP ICMP IGMP IP ARP RARP Ethernet drive An Ethernet frame

  6. Client-Server Model • Concurrent Server (in general, TCP server) 1. Wait for a client request to arrive 2. Start a new server to handle this client’s request new process, task, thread 3. the new server handles this client’s request 4. When complete, the new server terminates • Iterative server (in general, UDP server) • no multiple concurrent clients

  7. Port numbers • Application identification • Well known port numbers • FTP server: 21 • Telnet server: 23 • TFTP server: 69 • IANA (Internet Assigned Numbers Authority) • between 1 to 1023 • Unix specific services 256:1023 • Telnet vs. Rlogin • Client don’t care port numbers • unique on the host • ephemeral ports (1024 - 5000) • * solaris 2.2: start at 32768

  8. Port number repository on Unix • File • /etc/services • grep telnet /etc/services • telnet 23/tcp • grep domain /etc/services * reserved ports: 1-1023 • only used by process with superuser privilege

  9. Internet standard Organization • ISOC • IAB • 15 members • final editorial and technical review board • IETF • develop standard specifications • IRTF • long-term research projects

  10. RFCs • Official standards and information purposes • RFC index • replacement or update by a newer RFC • Important RFCs • The assigned Numbers RFC (1340) • Internet Official Protocol Standards RFC (1600) • state of standardization: standard, draft standard, proposed standard, experimental, informational, historic • requirement level: required, recommended, elective, limited user or not recommended • Host Requirements RFC (1122/1123) • link, network, transport, application layers • Router requirements RFC (1009)

  11. Standard simple services • Why Odd numbers for port number? • NCP used pair of odd-even connections • echo (port number 7) • discard (port number 9) • daytime (port number 13) • chargen (port number 19) • time (port number 37)

  12. TCP/IP implementations • UC at Berkely • API • sockets (“Berkely Sockets”) • TLI (Transport Layer Interface) - AT&T

  13. Link-Layer • Conveys • IP datagrams • ARP/RARP requests/replies • many types of networking hardware • token ring, FDDI, RS-232 • Ethernet • serial interfaces (SLIP and PPP) • loopback driver

  14. Ethernet and IEEE802 • 1982 by DEC, Intel and Xerox • CSMA/CD (Carrier Sense, Multiple Access with Collision Detection) • 10 Mbits/sec • 48-bit addresses • IEEE 802 • 802.3 (CSMA/CD), 802.4(token bus), 802.5 (token ring), 802.2 (LLC) • different frame format from Ethernet

  15. Host Requirements RFC for Ethernet 10Mbits/sec • Send and receive packets using RFC 894 (Ethernet encapsulation) • Receive RFC 1042 (IEEE 802) packets intermixed with RFC 894 packets • Send packets using RFC 1042 encapsulation

  16. Encapsulation (802.2/802.3) RFC 1042 Dest. address Source address length 802.3 MAC DSAP AA SSAP AA Cntr 03 802.2 LLC Org code 00 Type data CRC 802.2 SNAP Type IP datagram Type ARP request/reply PAD Type RARP request/reply PAD

  17. Encapsulation (Ethernet) RFC 894 Dest. address Source address length 802.3 MAC Type data CRC Type IP datagram Type ARP request/reply PAD Type RARP request/reply PAD

  18. IEEE 802 vs Ethernet • 802.3 allows 16-bit addresses • hardware address • ARP/RARP • map between 32-bit IP address / 48-bit address • non of the 802 length values is the same as the Ethernet type values • data size • 802: 38-1492 bytes • Ethernet: 46-1500 bytes

  19. Trailer encapsulation (893) • Rearrange the order of the fields in the IP datagram • variable-length fields (IP header and the TCP header) were moved to the end, right before CRC • data portion of the frame to be mapped to a hardware page, saving a memory-to-memory copy when the data is copied in the kernel • TCP data that is a multiple of 512 bytes in size can be moved by just manipulating the kernel’s page tables • Two hosts negotiated the use of trailer encapsulation using an extension of ARP • Different Ethernet frame type values are defined for these frames • Deprecated

  20. SLIP: Serial Line IP (RFC 1055) • Simple form of encapsulation for IP datagrams • Connecting Home systems to Internet • RS-232, high-speed modems • SLIP framing rules • IP datagram is started and terminated by the special character END (0xc0) • If a byte of the IP datagram equals the END character, • 2 byte sequence 0xdb (SLIP ESC character), 0xdc is transmitted instead • If a byte of the IP datagram equals the SLIP ESC character, the 2-byte sequence 0xdb, 0xdd is transmitted instead

  21. Difficiency of SLIP • Each end must know the other’s IP address • No type field • No checksum • upper layers provide some form of CRC • always a checksum for the IP header, TCP header and TCP data • newer modems can detect and correct corrupted frames • popular as the speed and reliability of modems increase

  22. Compressed SLIP • SLIP is • slow (19200 bits/sec below) • used for interactive traffic (Telnet, Rlogin) • many small TCP packets • To carry on3 byte of data, a 20-byte IP header and a 20-byte TCP header • CSLIP (Newer version): RFC 1144 • 3 or head 5 bytes er • maintains the stae of up to 16 tCP connections on each end of the CSLIP link • some of the fields in the two headers for a given conection normally don’t change • Of the fileds that do change, most change by a small positive amount

  23. PPP: Point-to-Point Protocol • Two kind of links • an asynchronous link with 8 bits of data and no parity • bit-oriented synchronous links • Link Control Protocol • establish, configure and test the data-link connection • each end negotiate various options • Family of network control protocols (NCPs) • specific to different network layer protocols (RFCs for IP, OSI network layer, DECnet and AppleTalk) • IP NCP: allows each end to specify if it can perform header compression)

  24. PPP encapsulation (RFC 1548) flag 7E Address FF Control 03 802.3 MAC protocol information CRC flag 7E Protocol 0021 IP datagram Protocol c021 Link control data Protocol 8021 Network control data

  25. Escaping for flag code, 0x7e • Synchronous link • done by hardware using bit stuffing • Asynchronous link • 0x7d is used for escape character • when 0x7d appears in a PPP frame, the character has had its sixth bit complemented • 0x7e is transmitted by 0x7d, 0x5e • 0x7d is transmitted by 0x7d, 0x5d • for ASCII control character, the sixth bit is turned on, for example, 0x01 is transmitted by 0x7d, 0x21 • it’s possible touse the link control protocol to specify which, if any, of these 32 values must be escaped

  26. SLIP- enhancement • Using Link control protocol • negotiate to omit the constant address and control fields and to reduce the protocol field form 2 bytes to 1 byte. • PPP overhead 3 bytes • 1 byte for the protocol field and 2 bytes for the CRC • SLIP 2 bytes • Using IP network control protocol, • negotiate to use Van Jacobson header compression

  27. Advantage of PPP over SLIP • Support for multiple protocols on a single serial line • CRC on every frame • Dynamic negotiation of the IP address for each end (using the IP network control protocol) • TCP/IP header compression • a link control protocol for negotiating many data-link options • The price • 3 bytes of additional overhead per frame • a few frames of negotiation when the link is established • more complex implementation

  28. Loopback interface • Allows a client and server on the same host to communicate with each other using TCP/IP • The class A network ID 127 is reserved for the loopback interface • IP address of 127.0.0.1 to this interface (local host) • An IP datagram sent to the loopback interface must not appear on any network • No short circuiting some of the transport layer logic and all of the network layer logic • complete processing of the data in the transport layer and network layer • seems inefficient, simplifies the design considering the loopback interface appears as just another link layer

  29. Processing of IP datagrams by loopback interface IP input function IP output function Destination IP address equal broadcast address or multicast address? Place on IP input queue Place on IP input queue yes no yes Loop back driver Destination IP address equal interface IP address? no ARP Demultiplex based on Ethernet frame type send recieve

  30. MTU (Maximum transmission unit) • Ethernet (1500), IEEE 802 (1492) • If IP datagram is larger than the MTU • fragmentation • Path MTU • smallest MTU of any data link that packets traverse between the two hosts • depends on route being used at any time • path MTU need not be the same in the two directions

  31. Serial Line Throughput Calculations • Line speed: 9600 bits/sec, 8 bits/byte, 1 start and 1 stop bits • line speed is 960 bytes/sec • transferring a 1024-byte packet takes 1066ms • with SLIP for an interactive application, along with an FTP that sends or receives 1024-byte packets, should wait on average 533ms to send interactive packets • type-of-service queueing: place interactive traffic ahead of bulk data traffic • an interactive response time longer than 100-200 ms is bad • round-trip time for a packet to be sent and response be returned ( normally a character echo)

  32. Serial Line Throughput Calculations • Reducing MTU of the SLIPO link to 256 • 133ms wait: half reducing • not perfect but good for bulk data transfer • Assuming 5-byte CSLIP header, 256 bytes of data • 98.1% of the line to data and 1.9% to headers • reducing MTU below 256 reduces the maximum throughput for bulk data transfers • MTU is a value that IP queries the link layer for • must include the normal TCP and IP headers • This is how IP makes its framentation decision • IP knows nothing about the header compression that CSLIP performs

  33. Serial Line Throughput Calculations • When only interactive traffic is being exchanged • 1 byte of data in each direction (assuming 5-byte compressed headers) takes around 12.5 ms for the round trip at 9600 bits/sec • compressing the headers from 40 bytes to 5 bytes reduces the round-trip time for the 1 byte of data from 85 to 12.5ms • For newer error correcting, compressing modems, difficult to calculate • the number of bytes sent over the network reduced • error correction may increase the amount of time to transfer these bytes

  34. IP (RFC 791) • TCP, UDP, ICMP, IGMP dta gets transmitted as IP datagrams • an unreliable, delivery service • Simple error handling algorithm • throw away the datagram and send an ICMP message back to the source • any required reliability should be provided by TCP • connectionless datagram • out of order delivery • each datagram may follow different route

  35. IP Header 32 (LSB) 0 (MSB) 4-bit version 4-bit header length 8-bit type of service (TOS) 16-bit total length (in bytes) 16-bit identification 3-bit flags 13-bit fragment offset 8-bit protocol 16-bit jeader checksum 8-bit time to live (TTL) 32-bit source IP address 32-bit destination IP address Options (if any) data

  36. IP header • Big endian (Network byte order) • Most signficant byte: first transmission • TOS: Minimize delay, Maximize throughput, Maximize reliability, Minimize monetary cost: only one bit can be turned on • not supported by most TCP/IP implementations • new routing protocols OSPF and IS-IS are based on this field • SLIP drivers provide type-of-service queueing, allowing interactive traffic to be handled before bulk data • it looks the protocol field to see if it’s a TCP segment and then checks the source and destination TCP port number to see if it’s for interactive service

  37. IP header • Big endian (Network byte order) • Most signficant byte: first transmission • TOS: Minimize delay, Maximize throughput, Maximize reliability, Minimize monetary cost: only one bit can be turned on • not supported by most TCP/IP implementations • new routing protocols OSPF and IS-IS are based on this field • SLIP drivers provide type-of-service queueing, allowing interactive traffic to be handled before bulk data • it looks the protocol field to see if it’s a TCP segment and then checks the source and destination TCP port number to see if it’s for interactive service

  38. Recommended values for type-of-service field • Telnet and Rlogin: minimum delay • FTP: maximum through put • SNMP: maximum reliability • NNTP: minimize monetary cost • ICMP: no setting

  39. IP Header • Maximum size of IP datagram: 65535 bytes • most data link layer fragment this • a host is not required to receive a datagram larger than 576 bytes • With UDP, numerous applications (RIP, TFTP, BOOTP,DNS, SNMP) limit to 512 bytes of user data • Most implementations (especially NFS allow for just over 8192-byte IP datagrams) • Some data links pad small frames to be a minimum length (Ethernet: 46 bytes) • total length enable to guess about what portion of Ethernet frame actually is IP datagram when the IP datagram is smaller than 46 bytes

  40. IP Header • Identification • uniquely identifies each datgram sent by a host • increments by one each time a datagram is sent • used for fragmentation and reassembly with flags and fragmentation offset • TTL • upper limit on the number of routers through which a datagram passes • decremented by on by every router • when reaches to 0, the datagram is thrown away and the sender is notified with ICMP message

  41. Header Checksum • Same checksum for ICMP, IGMP, UDP, TCP, IP • Checksum computing • the checksum = 0 • 16-bit one’s complement sum of the header • receiver verifies all one-bit checksum • IP discards the datagram, no error-message • a router often changes only the TTL filed • incrementally upodate the checksum without recalculating

  42. Options (variable-length list of optional information) • Security and handling restrictions • record rout • timestamp • loose source routing • strict source routing • always ends on a 32-bit boundary • IP header is always a multiple of 32 bits

  43. IP routing • When the destination is directed connected to the host or on a shared network • the IP datagram is sent directly to the destination • Otherwise • the host sends the datagram to a default router which will deliver the datagram to its destination • the host can be itself a router • A host embedding a router never forward datagram unless it is configured to to so • the IP layer has a routing table in memory that it searches each time it receives a datagram to send • When IP layer receives a datagram, if it contains its address or broadcasting address, it is sent to the protocol module in the protocol field, else the datagram is forwarded if configured to act as a router

  44. Entry of routing table • Destination address • complete host address (non-zero hostid) or network address (hostid 0 depending on the flag • IP address of a next-hop router or of a directly connected network • Flags • if destination address is host address or network address • if next-hop router is real next-hop router or a directly connected interface • Specification of which network interface the datagram should be passed to for transmission • Assumption • the next-hop router is closer to the destination than the sending host and the next-hop router is directly connected to the sending host

  45. IP routing action 1. Search the complete destination IP address (networkid and hostid) in the routing table (RT) • if found, send the packet to the indicated next-hop router or to the directly connected interface, point-to-point links 2. Search the destination network IP address (networkid) in the RT • if found, send the packet to the indicated next-hop router or to the directly connected interface • all the hosts on the destination network can be handled • must take into accout a possible subnet mask 3. Search the routing table for an entry labeled “default”, send the packet to the indicated next-hop router • if non-of these is successful, undeliverable message “host unreachable”, “network unreachable” ICMP message to the sending application • Default routes, along with the ICMP redirect message sent by a next-hop router, when forwarding fails

  46. IP routing example: from bsdi to sun Destination network = 140.252.13.0 bsdi sun .13.15 .13.33 Ethernet IP = 140.252.13 IP hdr Link hdr Destination IP = 140.252.13.33 Destination Ethernet of 140.252.13.33

  47. Link hdr IP hdr bsdi Ethernet IP = 140.252.1 .1.183 Next hop = 140.252.1.4 (default) netb modem SLIP IP hdr Destination IP = 192.48.96.9 modem .1.29 Next hop = 140.252.1.183 (default) bsdi sun .13.15 .13.33 Ethernet IP = 140.252.13 IP hdr Link hdr Destination IP = 192.48.96.9 Destination Ethernet of 140.252.13.33

  48. Subnet addressing • Host ID portion is divided into a subnet ID and a host ID (too many hostids for a network) • local system administrator decide to subnet or not • Class B IP address example Netid=140.252 8-bit hostid 8-bit subnetid • Allows 254 subnets, with 254 hosts per subnet • Subnetting hides the details of internal network organization • reduces the size of the Internet’s routing tables • only one routing table for all the subnetworks

  49. .57.0 192.68.189.0 .82.0 R57 .52.0 .53.0 .54.0 .55.0 .58.0 .60.0 R192 R82 R52 R53 R54 R55 R58 R60 KP .51.0 .81.0 140.252.104.1 Internet aix GATE solaris .1.4 .1.0 .1.92 .1.32 .1.11 .1.183 R2 R3 gem R4 R6 R7 R8 R10 netb .3.54 .2.0 .3.0 .4.0 .6.0 .7.0 .8.0 .9.0 .10.0 .11.0 .1.29 .13.65 .13.66 slip bsd svr sun R12 .13.35 .13.36 .13.0 .12.0

  50. Subnet mask • When host bootstraps • ip address, subnet mask is configured; 0xffffff00 = 255.255.255.0 • given its own IP Address and its subnet mask, a host know if a datagram is destined for • a host on its own subnet • a host on a different subnet on its own network • a host on a different network 1111111111111111 (networkid) 00000000 (hostid) 11111111 (subnetid)

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