Internet

Internet

IN2140: Introduction to Operating Systems and Data Communication Data Communication: Naming 1/27/20 Five Layer Reference, Internet Reference Model and a Comparison TCP/IP Reference Model Internet Architecture ISO-OSI presentation, session and application layer merged ISO-OSI data link layer and physical layer merged to form Network Interface 7 6 5 5 4 3 2 1/2 1 University of Oslo Application layer Presentation layer Application layer Session layer Transport layer Network layer Data link layer

Network interface layerlayer Physical IN2140 Introduction to operating systems and data communication Layers in General (OSI terminology) (N+1)entity (N+1)-layer (N+1)entity (N)-SAP (N)-entity (N)-layer (N)-protocol (N)-entity (N)-Layer abstraction level with defined tasks (N)-Service Access Point, (N)-SAP (N)-Entity active elements within a layer process or intelligent I/O module peer entities: corresponding entities on different systems service identification

describes how layer N provides a service for layer N+1 an Entity can offer several services (N)-Protocol University of Oslo a multitude of rules for transferring data between sameIN2140 Introduction to operating systems and data communication level entities Protocol: Communication between same Layers (N)-entity (N)-layer (N)-protocol Definition of protocol A protocol defines the format the order of messages exchanged between two or more communicating entities as well as the actions taken on transmission and/or reception of a message or other event It does not define the services offered to layer N+1 the services used (N-1-SAP) University of Oslo

(N)-entity Protocol Protocol syntax: rules for formatting Protocol semantics: rules for actions in case of a message or event Note: semantics must be defined as behaviour of all communicating peers Messages have lots of names protocol data unit (PDU) IN2140 Introduction to operating systems communicationpacket, message, and dataframe, TCP NF S SSH FTP TP HT SM TP RT P

Internet Protocol Stack UDP WANs LLC & MAC LANs physical MANs Nickname: Hourglass Model University of Oslo Transport layer Network layer IPv4 + IPv6 + ICMP + ARP ATM Application layer IN2140 Introduction to operating systems and data communication Data link and Physical layer How to send packets urgent urgent letter

letter from from Pl Pl to to IFI IFI signature signature needed needed !! To: To: Carsten Carsten IFI, IFI, UiO UiO Oslo, Oslo, Norway Norway To: To: IFI IFI To: To: IFI, IFI, UiO UiO Oslo, Oslo, Norway Norway To: To: Oslo Oslo

analogy fails a little bit because in the Internet dont wait, collect, and bundle To: To: Norway Norway very often analogy is right in the sense that we have some content to send, wrappers are put around itIN2140 for sending, and University of Oslo Introduction to operating systems and data communication Data flow through the network 7 4 3 1/2 End system address of next node peers peers peers peers 3 1/2 peers peers Intermediate system

address of remote machine address of remote process 7 4 3 1/2 End system data from application Each sending N-entity at layer N adds N-protocol information which is important for its peer N-entity and the receiving N-entity removes it before passing the data to layer N+1 University of Oslo IN2140 Introduction to operating systems and data communication Transport layer header: UDP example shown as 32 bits per line Source port Destination port Packet length Checksum

UDP header Data port the term in Internet protocol for the address of a process on an end system the transport layer address Note: there are several transport layer protocols in the TCP/IP world, UDP is shown because has the smallest header University of Oslo IN2140 Introduction to operating systems and data communication Network layer headers: IPv4 and IPv6 shown as 32 bits per line Version IHL Type DSCP of serviceECN Identification Time to live Total length D M

Protocol Fragment offset IPv4 Header Header checksum Source address (32 bit) Destination Address (32 bit) Data shown as 32 bits per line Version DSCP Flow label ECN Payload length IPv6 Header Next header Source address (128 bit) Destination Address (128 bit) Data

University of Oslo IN2140 Introduction to operating systems and data communication Hop Limit Data link layer headers: Ethernet example shown as 32 bits per line Ethernet Header Dest address (48 bits) Source addr (48 bits) Dest addr (cont) Source address (cont) length data data Ethernet Trailer data checksum University of Oslo IN2140 Introduction to operating systems and data communication checksum Network byte order Why do we use Big Endian numbers in layers 2 4 ?

Big vs Little Endian Representing numbers the decimal number 36 is identical to hexadecimal 24 for clarity we write 0x24 it identical to binary 100100 the bit pattern 1*32 + 0*16 + 0*8 + 1*4 + 0*2 + 0*1 we prefer to think in whole bytes, and may write 00100100 to it is hard to transform directly from decimal to sufficient binary think about but easy to transform from hexadecimal to binary 4 bits 00100100 0010 : 0100 time! 0*8 + 0*4 + 1*2 + 0*1 : 0*8 + 1*4 + 0*2 + 0*1 2 : 4 0x24 University of Oslo IN2140 Introduction to operating systems and data communication at a

Big vs Little Endian when we want a bigger number than 255 = 0xff , we need more than 8 bits = 1 byte to store it 1 byte 0 - 0xff 0 - 255 2 bytes 0 - 0xffff 0 - 65.535 4 bytes 0 - 0xffffffff 0 - 4.294.967.296 8 bytes 0 - 0xffffffffffffffff 0 - 1.844.674.407.370.9551.615 University of Oslo IN2140 Introduction to operating systems and data communication Big vs Little Endian It is very natural to write Hello and expect that it looks like this in code: char buffer[] = Hello; for( int i=0; i<5; i++ ) { printf(%c ,buffer[i]); } printf(\n); HH ee ll ll oo

lets create a number from its byte-sized pieces! when we use memory like this: unsigned char byte[4]; byte[0] = 0; byte[1] = 0; byte[2] = 2; byte[3] = 4; for( int i=0; i<4; i++ ) { printf(%x ,byte[i]); } printf(\n); int* ptr; ptr = (int*)&byte[0]; on on Intel Intel printf(hex %x\n,*ptr); WHY ? University of Oslo on on Sparc Sparc IN2140 Introduction to operating systems and data communication 00 00 22 44 hex hex 4020000 4020000 hex hex 204 204 Argument for Big Endian

compatible with western-world writing direction but when we use memory like this: unsigned char byte[8]; byte[0] = 0x81; for( int i=1; i<8; i++ ) byte[i] = 0; 81 81 00 00 00 00 00 00 00 00 00 00 00 00 00 00 unsigned char* ptr1 = (unsigned char*)&byte[0]; printf(%x\n, 1 + *ptr1); unsigned short* ptr2 = (unsigned short*)&byte[0]; printf(%x\n, 1 + *ptr2); unsigned int* ptr3 = (unsigned int*)&byte[0]; printf(%x\n, 1 + *ptr3); unsigned long long* ptr4 = (unsigned long long*)&byte[0]; printf(%llx\n, 1 + *ptr4); Big Big Endian Endian 82 82 8101 8101 81000001 81000001 8100000000000001

8100000000000001 University of Oslo IN2140 Introduction to operating systems and data communication Argument for Little Endian easy to transform when we use memory like this: unsigned char byte[8]; byte[0] = 0x81; for( int i=1; i<8; i++ ) byte[i] = 0; 81 81 00 00 00 00 00 00 00 00 00 00 00 00 00 00 unsigned char* ptr1 = (unsigned char*)&byte[0]; printf(%x\n, 1 + *ptr1); unsigned short* ptr2 = (unsigned short*)&byte[0]; printf(%x\n, 1 + *ptr2); unsigned int* ptr3 = (unsigned int*)&byte[0]; printf(%x\n, 1 + *ptr3); unsigned long long* ptr4 = (unsigned long long*)&byte[0]; printf(%llx\n, 1 + *ptr4); Little Little Endian Endian

82 82 82 82 82 82 82 82 cheap and easy to change the number of bytes used for an integer value harder for the human mind but faster to process University of Oslo IN2140 Introduction to operating systems and data communication Bonus for Big Endian L5 L4 L3 L3 L2 L2 L1 sends bytes to L4

passes packets to L3 adds a header for routing (and more) passes frame content to L2 adds frame header for addressing (and more) passes bits to L1 transfers bits L1 transfer starts at low memory addresses then continuing to high memory addresses speed matters headers are in front to process before all bits have arrived University of Oslo IN2140 Introduction to operating systems and data communication Bonus for Big Endian analogue in telephone numbers 0 0 1 7 3 2 5 6 2 8 6 2 9 wait ringing for wait ringing for more more country: area: country: North North America America

area: Central Central New New Jersey Jerseycity: city: Piscataway Piscataway IEEE IEEE office office 0 0 4 9 6 1 5 1 2 9 1 0 0 country: country: Germany Germany city: city: Darmstadt Darmstadt wait ringing for wait ringing for more more research research group group KOM KOM process first values that are sent first because only last provider knows interpretation ! University of Oslo

IN2140 Introduction to operating systems and data communication Bonus for Big Endian my lab machine in our lab network 129.240.66.59 this is called dotted decimal notation this style is the usual way of writing the old IPv4 address 0x81 F0 42 3B hexadecimal representation of the 4 bytes of the address 10000001 11110000 01000010 00111011 binary representation of the 4 bytes University of Oslo IN2140 Introduction to operating systems and data communication Bonus for Big Endian my lab machine in our lab network 129.240.66.59 0x81 F0 42 3B 10 000 00 1 1 111 00 00 0 100 00 10 001 11 011 University University of of Oslo Oslo lab lab network network my

my lab lab machine machine University University of of Oslo Oslo decides decides the the number number of of bits bits for for each each internal internal subnet subnet most most significant significant for for finding finding aa computer computer (covering (covering the the long long distances) distances) University of Oslo least least significant

significant for for finding finding aa computer computer (covering (covering the the short short distances) distances) IN2140 Introduction to operating systems and data communication Bonus for Big Endian my lab machine in our lab network 129.240.66.59 0x81 F0 42 3B most most significant significant byte byte these these are are 4 4 bytes, bytes, they they are are often often represented represented as as aa long long in

in programs programs least least significant significant byte byte but building this address on a Little Endian machine is dangerous University of Oslo IN2140 Introduction to operating systems and data communication Bonus for Big Endian but building this address on a Little Endian machine is dangerous: int main() { int a = ( 0x81 int b = ( 0xf0 int c = ( 0x42 int d = 0x3b; int addr = a | 81000000 81000000 << 24 ); << 16 ); << 8 ); b | c | d; unsigned char* ptr =

(unsigned char*)&addr; printf("%x\n",addr); printf("%x ",ptr[0]); printf("%x ",ptr[1]); printf("%x ",ptr[2]); printf("%x\n",ptr[3]); 00f00000 00f00000 00004200 00004200 0000003b 0000003b 81f0423b 81f0423b 81f0423b 81f0423b 3b 3b 42 42 f0 f0 81 81 } University of Oslo IN2140 Introduction to operating systems and data communication Addressing MAC addresses in the TCP/IP model Addressing

network is sub-network (subnet) of network intermediate system end system University of Oslo IN2140 Introduction to operating systems and data communication Addressing end system intermediate system network Point-to-point channels Gigabit Ethernet (1GB Ethernet) University of Oslo MAC addresses are not required in a true point-to-point network when L2 passes

frames to the correct L1 entity, the unique peer L1 entity will receive it IN2140 Introduction to operating systems and data communication Addressing end systems intermediate system network MAC addresses are important in a true broadcast network Challenge MAC addresses have only local meaning nodes on the other side of an IS do not know them University of Oslo Broadcasting channels Cable old-fashioned Ethernet Radio WiFi (IEEE 802.11)

IN2140 Introduction to operating systems and data communication Addressing end systems intermediate system network Point-to-point channels Gigabit Ethernet (1GB Ethernet) Broadcasting channels Cable old-fashioned Actually, Gigabit Ethernet behaves Ethernet University of Oslo like old-fashioned Ethernet. 2 good reasons: backward compatibility no management needed when a PC is unplugged in one place and plugged back in elsewhere IN2140 Introduction to operating systems and data communication

Address resolution network end systems intermediate system given a packet with an L3 address, an IS must find the correct L2 address for this packet quickly what are the options? University of Oslo IN2140 Introduction to operating systems and data communication Address resolution end systems intermediate system network Internet address e.g. 129.31.65.7 ? Netadapter address e.g. Ethernet address 00:08:74:35:2b:0a Problem Potentially every link can use a different L2 protocol

NRK Telen or serve 10GB Eth router r ES IS DSL DSL mode m WiFi 1GB Eth router IS IS WiFi desktop ES Different L2 protocols have different address styles IP address must be mapped onto the MAC address 48 bit for Ethernet and WiFi, DSL may use 20 or 48 bits University of Oslo IN2140 Introduction to operating systems and data communication

Address resolution: Ethernet example Ethernet Header Dest address (48 bits) Source addr (48 bits) Dest addr (cont) Source address (cont) length data data Ethernet Trailer data checksum checksum MAC address structure Ethernet and WiFi are L2 layers using EUI-48 Extended Unique Identifier with 48 bits 6 bytes, written like this: f2:18:98:3a:b8:97 to recognize easily that the text is supposed to mean a MAC address Ethernet MAC addresses should be globally unique University of Oslo IN2140 Introduction to operating systems and data communication Address resolution: Ethernet example Ethernet Header

Dest address (48 bits) Source addr (48 bits) Dest addr (cont) Source address (cont) length data data Ethernet Trailer data checksum checksum IANA and IEEE decide how to split the address space first 3 bytes explain whether an address is special OR first 3 bytes determine who owns the address range e.g.: IANA - Internet Assigned Number F0:18-98 : Apple, Inc. Authority 78:45:C4: Dell Inc. IEEE - Institute of Electrical and 00:50:56: VMWare, Inc. Electronics Engineers University of Oslo IN2140 Inc. Introduction to operating systems and data communication B8:AC:6F: Dell

Addresses my lab machines MAC addresses: Ethernet MAC WiFi MAC University of Oslo IN2140 Introduction to operating systems and data communication Addresses my lab machines MAC addresses: Ethernet MAC WiFi MAC University of Oslo IN2140 Introduction to operating systems and data communication Addresses MAC addresses known to my lab machine DSL Modems Ethernet MAC MAC addresses know to nordur, one of the login.ifi.uio.no machines (incomplete) University of Oslo IN2140 Introduction to operating systems and data communication Address Resolution 1st idea: direct mapping

the 32 bit destination IP address would fit into the 48 bit destination MAC address shown as 32 bits per line Dest address (48 bits) Source addr (48 bits) Dest addr (cont) Source address (cont) length data Version IHL PRE Type of service ToS Data Identification but: there is a new MAC address Time to live data checksum D M

Protocol does not work for the Internet Fragment offset checksum Header checksum Source address (32 bit) Destination Address (32 bit) for every pair of direct neighbours need to re-write the destination IP address on every IS but IP addresses are globally unique University of Oslo Total length IN2140 Introduction to operating systems and data communication Data Address Resolution 2nd idea: mapping table network end systems intermediate system

every node maintains a table that maps IP address MAC address for all every network interface and for every directly reachable node (L2 neighbour) idea 2.1: manually maintained by people a lot of work, but not unrealistic IFI allows only well-known MAC addresses in well-known network plugs could be used for this but is not idea 2.2: established by broadcasts from stations University of Oslo IN2140 Introduction to operating systems and data communication Address Resolution 3nd idea: address resolution protocol network end systems intermediate system node with a packet to deliver: if a local cache contains IP address MAC address send packet & update cache removal timeout else send broadcast to all stations Who has IP address? if one node responds add IP address MAC address mapping to cache set timeout for removal from cache to some minutes send packet else drop packet

University of Oslo IN2140 Introduction to operating systems and data communication Address Resolution Protocol (ARP) H H H H H ARP Request source @IP: 9.228.50.8 @HW: 0xaa target @IP: 9.228.50.3 @HW: ARP Response source @IP: 9.228.50.3 @HW: 0xa3e target @IP: 9.228.50.8 @HW: 0xaa University of Oslo IN2140 Introduction to operating systems and data communication @IP: 9.228.50.3

@HW: 0xa3e Address Resolution Protocol (ARP) ES 1 ES 1 1GB Ethernet End system not directly available by broadcast Example: ES 1 to ES 2 1GB Ethernet UNINETTs N x 10GB Ethernet ARP would not receive a response Ethernet broadcast is not rerouted over a router Solution 1: proxy ARP ES ES 2 2 1GB Ethernet the local router knows all remote networks with their respective routers responds to local ARP

local ES 1 sends data for ES 2 always to the local router, this router forwards the data (by interpreting the IP address contained in the data) Solution 2: remote network address is known local ES 1 sends data to the appropriate remote router local router forwards packets University of Oslo IN2140 Introduction to operating systems and data communication Reverse Address Resolution Protocol (RARP) Retrieve Internet address from knowledge of hardware address H H @IP: unknown Application today: @HW: 0xaa blades in large clusters are physically moved H source @IP: @HW: 0xaa target @HW: 0xaa RARP Response source

@IP: 9.228.50.3 University of Oslo H RARP Request @IP: for other uses mostly replaced by newer protocols BOOTP and DHCP H @HW: 0xa3e target @IP: 9.228.50.8 @HW: 0xaa IN2140 Introduction to operating systems and data communication @IP: 9.228.50.3 @HW: 0xa3e RARP server responds RARP server has to be available on the LAN Addressing IP addresses

in the TCP/IP model Internet Addresses and Internet Subnetworks Original global addressing concept for the Internet For addressing end systems and intermediate systems each network interface (not ES) has its own unique address 5 classes 7 Network A 0 B 10 C 110 24 Host 14 Network 1110 1111 16 Host 21

Network 8 Host 28 Multicast address 28 Reserved ICANN (Internet Corporation for Assigned Numbers and Names) manages network numbers delegates parts of the address space to regional authorities University of Oslo IN2140 Introduction to operating systems and data communication Internet Address and Internet Subnetworks Networks grow and should be somehow structured several networks instead of one preferable but getting several address areas is hard since address space is limited e.g., university may have started with class B address, doesnt get second one Problem class A, B, C refer to one network, not collection of LANs Allow a network to be split into several parts for internal use still look like single network to outside world University of Oslo

IN2140 Introduction to operating systems and data communication Internet Address and Internet Subnetworks Idea local decision for subdividing host share into subnetwork portion and end system portion e.g. address 129.8.7.2: 10 14 Network 6 Subnet 16 10 Host Host 10000001000010000000011100000010 & & Subnet mask: 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 Subnet address: 10000001000010000000010000000000 To write down subnet address with subnet mask use either 129.8.4.0/255.255.252.0

or 129.8.4.0/22 Use subnet mask to distinguish network and subnet part from host part Routing with 3 levels of hierarchy Algorithm in router (by masking bits: AND between address and subnet mask): packet to another network (yes, then to this router) packet to local end system (yes, then deliver packet) packet to other subnetwork (yes, then reroute to appropriate router) University of Oslo IN2140 Introduction to operating systems and data communication CIDR: Classless InterDomain Routing Subnetting not good enough Too many organizations require addresses in principle many addresses due to 32-bit address space but inefficient allocation due to class-based organization class A network with 16 million addresses too big for most cases class C network with 256 addresses is too small most organizations are interested in class B network, but there are only 16384 (in reality, class B too large for many organizations) Large number of networks leads to large routing tables Introduction of CIDR (Classless InterDomain Routing) (RFC1519)

CIDR Principle to allocate IP addresses in variable-sized blocks (without regard to classes) e.g., request for 2000 addresses would lead to assignment of 2048 address block starting on 2048 byte boundary but, dropping classes makes forwarding more complicated University of Oslo IN2140 Introduction to operating systems and data communication CIDR: Classless InterDomain Routing Search for longest matching prefix if several entries with different subnet mask length may match then use the one with the longest mask i.e., AND operation for address & mask must be done for each table entry Entries may be aggregated to reduce routing tables 194.24.0.0/21 Router 194.24.8.0/22 194.24.0.0/19 Router

Router Unassigned 194.24.16.0/20 University of Oslo Router IN2140 Introduction to operating systems and data communication 194.24.12.0/22 IP Version 6 (IPv6) Motivation for IPv6: problems with IPv4 Too few addresses Bad support for QoS Bad support for mobility Many other shortcomings IANA: IANA: Internet Internet assigned assigned numbers numbers authority authority RIR: RIR: regional regional Internet Internet registry registry Example Example consequences: consequences:

no no IP IP addresses addresses for for individuals individuals large-scale large-scale sharing sharing of of Internet Internet addresses addresses in in local local networks networks using using NAT NAT Microsoft Microsoft using using addresses addresses from from RIR RIR LACNIC LACNIC (Latin (Latin America America & & Caribbean Caribbean NIC) NIC) for

for Cloud Cloud nodes nodes in in North North America America [by Mro, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=10593349] University of Oslo IN2140 Introduction to operating systems and data communication IPv6 Objectives To support billions of end systems longer addresses To reduce routing tables To simplify protocol processing Scalability simplified header To increase security security means integrated To support real-time data traffic flow label, traffic class To provide multicasting To support mobility (roaming) Addressing IPv4

limitations To be open for change (future) extension headers To coexist with existing protocols University of Oslo Coexistance IN2140 Introduction to operating systems and data communication IPv4 and IPv6 shown as 32 bits per line Version IHL Type DSCP of service ECN Identification Time to live Total length DM Protocol Fragment offset Header checksum IPv4 Header

Source address (32 bit) Destination Address (32 bit) Options (0 or more) L4 Data shown as 32 bits per line New New IPv6 IPv6 header header is is larger larger but but simpler simpler IPv6 Header Version DSCP ECN Payload length Flow label Next header Source address (128 bit) packet packet can can never

never be be Destination Address (128 bit) fragmented, fragmented, now now an an L4 L4 task task L4 Data options options are are now now payload payload checksum is an University of Oslo checksum is now nowIN2140 an Introduction to operating systems and data communication Hop Limit IPv6 addresses example of the IPv6 address spaces shown as 64 bits per line network prefix interface identifier

subnet identifier a typical routed address IPv6 addresses are written in sets of 2 bytes in hexadecimal notation, sets of zero can be compressed example www.google.com: 2a00:1450:400f:80a::2004 which is an abbreviation for 2a00:1450:400f:080a:0000:0000:0000:2004 this address is part of the network 2a00:1450:400f::/48 which is known to be used by Google since 12/2018 University of Oslo IN2140 Introduction to operating systems and data communication IPv6 addresses example of the IPv6 address spaces shown as 64 bits per line network prefix interface identifier subnet identifier a typical routed address one idea is to use the MAC address of a computer for the

interface identifier part of its global and link-local address it may also be requested from a server or assigned by other means University of Oslo IN2140 Introduction to operating systems and data communication IPv6 addresses example of the IPv6 address spaces shown as 64 bits per line 1111111010 all zeroes interface identifier a link-local address link-local addresses cannot be routed example IPv6 address of austur.ifi.uio.no: fe80::baac:6fff:fed2:6ba0 which is an abbreviation for fe80:0000:0000:0000:baac:6fff:fed2:6ba0x for us, so far mostly worthless because not routed University of Oslo IN2140 Introduction to operating systems and data communication

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