2002 년 2 학기인터넷통신망 년 2 학기

인터넷통신망 2 Acknowledgement Some figures and texts are from: –Govindan –Kurose –Peterson & Davie –Huitema –Halabi –Retana, Slice & White

2002 년 2 학기인터넷통신망 3 Internetworking Outline Best Effort Service Model Global Addressing Scheme

2002 년 2 학기인터넷통신망 4 IP Internet Concatenation of Networks Protocol Stack R2 R1 H4 H5 H3 H2 H1 Network 2 (Ethernet) Network 1 (Ethernet) H6 Network 3 (FDDI) Network 4 (point-to-point) H7R3H8 R1 ETH FDDI IP ETH TCP R2 FDDI PPP IP R3 PPP ETH IP H1 IP ETH TCP H8

2002 년 2 학기인터넷통신망 5 Service Model Connectionless (datagram-based) Best-effort delivery (unreliable service) –packets are lost –packets are delivered out of order –duplicate copies of a packet are delivered –packets can be delayed for a long time

2002 년 2 학기인터넷통신망 6 IP datagram format ver length 32 bits data (variable length, typically a TCP or UDP segment) 16-bit identifier Internet checksum time to live 32 bit source IP address IP protocol version number header length (bytes) max number remaining hops (decremented at each router) for fragmentation/ reassembly total datagram length (bytes) upper layer protocol to deliver payload to head. len type of service “type” of data flgs fragment offset upper layer 32 bit destination IP address Options (if any) E.g. timestamp, record route taken, pecify list of routers to visit.

2002 년 2 학기인터넷통신망 7 Datagram networks: the Internet model no call setup at network layer routers: no state about end-to-end connections –no network-level concept of “connection” packets typically routed using destination host ID –packets between same source-dest pair may take different paths application transport network data link physical application transport network data link physical 1. Send data 2. Receive data

2002 년 2 학기인터넷통신망 8 Network layer service models: Network Architecture Internet ATM Service Model best effort CBR VBR ABR UBR Bandwidth none constant rate guaranteed rate guaranteed minimum none Loss no yes no Order no yes Timing no yes no Congestion feedback no (inferred via loss) no congestion no congestion yes no Guarantees ? Internet model being extented: Intserv, Diffserv

2002 년 2 학기인터넷통신망 9 Fragmentation and Reassembly Each network has some MTU Strategy –fragment when necessary (MTU < Datagram) –try to avoid fragmentation at source host –re-fragmentation is possible –fragments are self-contained datagrams –use CS-PDU (not cells) for ATM –delay reassembly until destination host –do not recover from lost fragments

2002 년 2 학기인터넷통신망 10 Example Ident = xOffset = 0 Start of header 0 Rest of header 1400 data bytes Ident = xOffset = 0 Start of header 1 Rest of header 512 data bytes Ident = xOffset = 512 Start of header 1 Rest of header 512 data bytes Ident = xOffset = 1024 Start of header 0 Rest of header 376 data bytes

2002 년 2 학기인터넷통신망 11 IP Fragmentation & Reassembly network links have MTU (max.transfer size) - largest possible link-level frame. –different link types, different MTUs large IP datagram divided (“fragmented”) within net –one datagram becomes several datagrams –“reassembled” only at final destination –IP header bits used to identify, order related fragments fragmentation: in: one large datagram out: 3 smaller datagrams reassembly

2002 년 2 학기인터넷통신망 12 IP Fragmentation and Reassembly ID =x offset =0 fragflag =0 length =4000 ID =x offset =0 fragflag =1 length =1500 ID =x offset =1480 fragflag =1 length =1500 ID =x offset =2960 fragflag =0 length =1040 One large datagram becomes several smaller datagrams

2002 년 2 학기인터넷통신망 13 Global Addresses Properties –globally unique –hierarchical: network + host Dot Notation – – – NetworkHost A: NetworkHost B: NetworkHost C:

2002 년 2 학기인터넷통신망 14 Datagram Forwarding Strategy –every datagram contains destination’s address –if directly connected to destination network, then forward to host –if not directly connected to destination network, then forward to some router –forwarding table maps network number into next hop –each host has a default router –each router maintains a forwarding table Example (R2) Network Number Next Hop 1 R3 2 R1 3 interface 1 4 interface 0

2002 년 2 학기인터넷통신망 15 Address Translation Map IP addresses into physical addresses –destination host –next hop router Techniques –encode physical address in host part of IP address –table-based ARP –table of IP to physical address bindings –broadcast request if IP address not in table –target machine responds with its physical address –table entries are discarded if not refreshed

2002 년 2 학기인터넷통신망 16 ARP Details Request Format –HardwareType: type of physical network (e.g., Ethernet) –ProtocolType: type of higher layer protocol (e.g., IP) –HLEN & PLEN: length of physical and protocol addresses –Operation: request or response –Source/Target-Physical/Protocol addresses Notes –table entries timeout in about 10 minutes –update table with source when you are the target –update table if already have an entry –do not refresh table entries upon reference

2002 년 2 학기인터넷통신망 17 ARP Packet Format TargetHardwareAddr (bytes 2–5) TargetProtocolAddr (bytes 0–3) SourceProtocolAddr (bytes 2–3) Hardware type = 1ProtocolType = 0x0800 SourceHardwareAddr (bytes 4–5) TargetHardwareAddr (bytes 0–1) SourceProtocolAddr (bytes 0–1) HLen = 48PLen = 32Operation SourceHardwareAddr (bytes 0–3)

2002 년 2 학기인터넷통신망 18 LAN Addresses and ARP 32-bit IP address: network-layer address used to get datagram to destination network (recall IP network definition) LAN (or MAC or physical) address: used to get datagram from one interface to another physically-connected interface (same network) 48 bit MAC address (for most LANs) burned in the adapter ROM

2002 년 2 학기인터넷통신망 19 LAN Addresses and ARP Each adapter on LAN has unique LAN address

2002 년 2 학기인터넷통신망 20 LAN Address (more) MAC address allocation administered by IEEE manufacturer buys portion of MAC address space (to assure uniqueness) Analogy: (a) MAC address: like Social Security Number (b) IP address: like postal address MAC flat address => portability –can move LAN card from one LAN to another IP hierarchical address NOT portable – depends on network to which one attaches

2002 년 2 학기인터넷통신망 21 Link layer headers A B E Starting at A, given IP datagram addressed to B: look up net. address of B, find B on same net. as A link layer send datagram to B inside link-layer frame B’s MAC addr A’s MAC addr A’s IP addr B’s IP addr IP payload datagram frame frame source, dest address datagram source, dest address

2002 년 2 학기인터넷통신망 22 ARP: Address Resolution Protocol Each IP node (Host, Router) on LAN has ARP module, table ARP Table: IP/MAC address mappings for some LAN nodes –TTL (Time To Live): time after which address mapping will be forgotten (typically 20 min) Question: how to determine MAC address of B given B’s IP address?

2002 년 2 학기인터넷통신망 23 ARP protocol A knows B's IP address, wants to learn physical address of B A broadcasts ARP query pkt, containing B's IP address –all machines on LAN receive ARP query B receives ARP packet, replies to A with its (B's) physical layer address A caches (saves) IP-to-physical address pairs until information becomes old (times out) –soft state: information that times out (goes away) unless refreshed

2002 년 2 학기인터넷통신망 24 Routing to another LAN walkthrough: routing from A to B via R A R B

2002 년 2 학기인터넷통신망 25 A creates IP packet with source A, destination B A uses ARP to get R’s physical layer address for A creates Ethernet frame with R's physical address as dest, Ethernet frame contains A-to-B IP datagram A’s data link layer sends Ethernet frame R’s data link layer receives Ethernet frame R removes IP datagram from Ethernet frame, sees its destined to B R uses ARP to get B’s physical layer address R creates frame containing A-to-B IP datagram sends to B A R B

2002 년 2 학기인터넷통신망 26 Ethernet “dominant” LAN technology: cheap $20 for 100Mbs! first wildey used LAN technology Simpler, cheaper than token LANs and ATM Kept up with speed race: 10, 100, 1000 Mbps Metcalfe’s Etheret sketch

2002 년 2 학기인터넷통신망 27 Ethernet Frame Structure Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame Preamble: 7 bytes with pattern followed by one byte with pattern used to synchronize receiver, sender clock rates

2002 년 2 학기인터넷통신망 28 Internet Control Message Protocol (ICMP) Echo (ping) Redirect (from router to source host) Destination unreachable (protocol, port, or host) TTL exceeded (so datagrams don’t cycle forever) Checksum failed Reassembly failed Cannot fragment

2002 년 2 학기인터넷통신망 29 ICMP: Internet Control Message Protocol used by hosts, routers, gateways to communication network-level information –error reporting: unreachable host, network, port, protocol –echo request/reply (used by ping) network-layer “above” IP: –ICMP msgs carried in IP datagrams ICMP message: type, code plus first 8 bytes of IP datagram causing error Type Code description 0 0 echo reply (ping) 3 0 dest. network unreachable 3 1 dest host unreachable 3 2 dest protocol unreachable 3 3 dest port unreachable 3 6 dest network unknown 3 7 dest host unknown 4 0 source quench (congestion control - not used) 8 0 echo request (ping) 9 0 route advertisement 10 0 router discovery 11 0 TTL expired 12 0 bad IP header

2002 년 2 학기인터넷통신망 30 Virtual Networks and Tunnels VPN(Virtual Private Network) –Logically private over shared network –Use IP tunneling(encapsulation, IP in IP)

2002 년 2 학기인터넷통신망 31 Tunneling example(IPv6 over IPv4) tunnel end-node (entry-point) tunnel end-node (exit-point) original packet tunnel Tunnel packet Generic Packet Tunneling in IPv6 Specification (internet-draft, S. deering, July 2002)

2002 년 2 학기인터넷통신망 32 Problem of firewall Drop IPv6 tunneling packets

2002 년 2 학기인터넷통신망 33 Limitation of firewall IP-Protocol-41 filtering

2002 년 2 학기인터넷통신망 34 Experiment (KAME) Network topology

2002 년 2 학기인터넷통신망 35 Experiment (KAME) Result : KAME (gif tunneling)

2002 년 2 학기인터넷통신망 36 Experiment (KAME) Result : KAME (gif tunneling)

2002 년 2 학기인터넷통신망 37 Solution:Double encapsulation

2002 년 2 학기인터넷통신망 38 Experiment (D-encap) Result : D-encap

2002 년 2 학기인터넷통신망 39 Experiment (D-encap) Result : D-encap