Computer Networking CCS-2201/CE-231 Introduction to Networks PDF

Computer Networking CCS-2201/CE-231: Introduction to Networks Dr. Ehab Abousaif PhD in Electrical and Computer Eng., University of Idaho, USA IEEE member, IMAPS member College of Computing and Information Technology, AASTMT Cell: 01114757888 Email: [email protected] Chapter 4 Network Layer:...

Computer Networking CCS-2201/CE-231: Introduction to Networks Dr. Ehab Abousaif PhD in Electrical and Computer Eng., University of Idaho, USA IEEE member, IMAPS member College of Computing and Information Technology, AASTMT Cell: 01114757888 Email: [email protected] Chapter 4 Network Layer: Computer Networking: A Data Plane Top-Down Approach A note on the use of these PowerPoint slides: 8th edition  These slides are based on the original slides made by the authors of the book. Jim Kurose, Keith Ross  These slides are a modified version of the original slides and have the same copyrights for Pearson, 2020 the authors and for Dr. Ehab Abousaif who modify the slides and put it into this final form. Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-1 Network layer: our goals understand principles  instantiation, implementation behind network layer in the Internet services, focusing on data IP protocol plane: NAT network layer service models forwarding versus routing how a router works addressing generalized forwarding Internet architecture Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-2 Network layer: “data plane” roadmap  Network layer: overview data plane control plane  What’s inside a router input ports, switching, output ports buffer management, scheduling  IP: the Internet Protocol  Generalized Forwarding, SDN datagram format Match+action addressing OpenFlow: match+action in action network address translation IPv6 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-3 Network-layer services and protocols  transport segment from sending mobile network to receiving host national or global ISP sender: encapsulates segments into datagrams, passes to link layer application receiver: delivers segments to transport network transport layer protocol link physical network  network layer protocols in every network link link physical physical Internet device: hosts, routers network  routers: link network physical link physical network datacenter examines header fields in all IP link physical network datagrams passing through it application moves datagrams from input ports to transport network output ports to transfer datagrams enterprise network link physical along end-end path Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-4 Two key network-layer functions network-layer functions: analogy: taking a trip  forwarding: move packets from  forwarding: process of getting a router’s input link to through single interchange appropriate router output link  routing: process of planning trip  routing: determine route taken from source to destination by packets from source to destination routing algorithms forwarding routing Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-5 Network layer: data plane, control plane Data plane: Control plane  local, per-router function  network-wide logic  determines how datagram  determines how datagram is arriving on router input port routed among routers along end- is forwarded to router end path from source host to output port destination host values in arriving  two control-plane approaches: packet header traditional routing algorithms: 0111 1 implemented in routers 2 3 software-defined networking (SDN): implemented in (remote) servers Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-6 Per-router control plane Individual routing algorithm components in each and every router interact in the control plane Routing Algorithm control plane data plane values in arriving packet header 0111 1 2 3 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-7 Software-Defined Networking (SDN) control plane Remote controller computes, installs forwarding tables in routers Remote Controller control plane data plane CA CA CA CA CA values in arriving packet header 0111 1 2 3 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-8 Network service model Q: What service model for “channel” transporting datagrams from sender to receiver? example services for example services for a flow of individual datagrams: datagrams:  guaranteed delivery  in-order datagram delivery  guaranteed delivery with  guaranteed minimum bandwidth less than 40 msec delay to flow  restrictions on changes in inter- packet spacing Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-9  Network-layer service model Quality of Service (QoS) Guarantees ? Network Service Architecture Model Bandwidth Loss Order Timing Internet best effort none no no no ATM Constant Bit Rate Constant rate yes yes yes Internet “best effort” service model ATM NoAvailable guaranteesBit Rate on: Guaranteed min no yes no Internet i. successful Intserv Guaranteeddatagram yes delivery to yesdestination yes yes ii. 1633 (RFC timing ) or order of delivery Internet iii. bandwidth Diffserv (RFC 2475) available to end-end possible flow possibly possibly no Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-10  Network-layer service model Quality of Service (QoS) Guarantees ? Network Service Architecture Model Bandwidth Loss Order Timing Internet best effort none no no no ATM Constant Bit Rate Constant rate yes yes yes ATM Available Bit Rate Guaranteed min no yes no Internet Intserv Guaranteed yes yes yes yes (RFC 1633) Internet Diffserv (RFC 2475) possible possibly possibly no Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-11 Reflections on best-effort service:  simplicity of mechanism has allowed Internet to be widely deployed adopted  sufficient provisioning of bandwidth allows performance of real-time applications (e.g., interactive voice, video) to be “good enough” for “most of the time”  replicated, application-layer distributed services (datacenters, content distribution networks) connecting close to clients’ networks, allow services to be provided from multiple locations  congestion control of “elastic” services helps Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-12 Network layer: “data plane” roadmap  Network layer: overview data plane control plane  What’s inside a router input ports, switching, output ports buffer management, scheduling  IP: the Internet Protocol datagram format  Generalized Forwarding, SDN addressing Match+action network address translation OpenFlow: match+action in action IPv6 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-13 Router architecture overview high-level view of generic router architecture: routing, management routing control plane (software) processor operates in millisecond time frame forwarding data plane (hardware) operates in nanosecond timeframe high-speed switching fabric router input ports router output ports Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-14  Input port functions lookup, link layer forwarding line switch termination protocol fabric (receive) queueing physical layer: bit-level reception link layer: decentralized switching: e.g., Ethernet  using header field values, lookup output port using forwarding table in input port memory (“match plus action”) (chapter 6)  goal: complete input port processing at ‘line speed’  input port queuing: if datagrams arrive faster than forwarding rate into switch fabric Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-15  Input port functions lookup, link layer forwarding line switch termination protocol fabric (receive) queueing physical layer: bit-level reception link layer: decentralized switching: e.g., Ethernet  using header field values, lookup output port using forwarding table in input port memory (“match plus action”) (chapter 6)  destination-based forwarding: forward based only on destination IP address (traditional)  generalized forwarding: forward based on any set of header field values Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-16 Destination-based forwarding 3 Q: but what happens if ranges don’t divide up so nicely? Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-17 Longest prefix matching longest prefix match when looking for forwarding table entry for given destination address, use longest address prefix that matches destination address. Destination Address Range Link interface 11001000 00010111 00010*** ******** 0 11001000 00010111 00011000 ******** 1 11001000 00010111 00011*** ******** 2 otherwise 3 11001000 00010111 00010110 10100001 which interface? examples: 11001000 00010111 00011000 10101010 which interface? Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-18 Longest prefix matching longest prefix match when looking for forwarding table entry for given destination address, use longest address prefix that matches destination address. Destination Address Range Link interface 11001000 00010111 00010*** ******** 0 11001000 00010111 00011000 ******** 1 11001000 match! 00010111 00011*** ******** 2 otherwise 3 11001000 00010111 00010110 10100001 which interface? examples: 11001000 00010111 00011000 10101010 which interface? Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-19 Longest prefix matching longest prefix match when looking for forwarding table entry for given destination address, use longest address prefix that matches destination address. Destination Address Range Link interface 11001000 00010111 00010*** ******** 0 11001000 00010111 00011000 ******** 1 11001000 00010111 00011*** ******** 2 otherwise 3 match! 11001000 00010111 00010110 10100001 which interface? examples: 11001000 00010111 00011000 10101010 which interface? Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-20 Longest prefix matching longest prefix match when looking for forwarding table entry for given destination address, use longest address prefix that matches destination address. Destination Address Range Link interface 11001000 00010111 00010*** ******** 0 11001000 00010111 00011000 ******** 1 11001000 00010111 00011*** ******** 2 otherwise 3 match! 11001000 00010111 00010110 10100001 which interface? examples: 11001000 00010111 00011000 10101010 which interface? Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-21 Longest prefix matching  we’ll see why longest prefix matching is used shortly, when we study addressing  longest prefix matching: often performed using ternary content addressable memories (TCAMs) content addressable: present address to TCAM: retrieve address in one clock cycle, regardless of table size Cisco Catalyst: ~1M routing table entries in TCAM Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-22 Switching fabrics  transfer packet from input link to appropriate output link  switching rate: rate at which packets can be transfer from inputs to outputs often measured as multiple of input/output line rate N inputs: switching rate N times line rate desirable R (rate: NR, R ideally)...... N input ports high-speed N output ports switching fabric R R Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-23 Switching fabrics  transfer packet from input link to appropriate output link  switching rate: rate at which packets can be transfer from inputs to outputs often measured as multiple of input/output line rate N inputs: switching rate N times line rate desirable  three major types of switching fabrics: memory memory bus interconnection network Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-24 Switching via memory first generation routers:  traditional computers with switching under direct control of CPU  packet copied to system’s memory  speed limited by memory bandwidth (2 bus crossings per datagram) input output port memory port (e.g., (e.g., Ethernet) Ethernet) system bus Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-25 Switching via a bus datagram from input port memory to output port memory via a shared bus bus contention: switching speed limited by bus bandwidth 32 Gbps bus, Cisco 5600: sufficient speed for access routers Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-26 Switching via interconnection network  Crossbar, Clos networks, other interconnection nets initially developed to connect processors in multiprocessor  multistage switch: nxn switch from 3x3 crossbar multiple stages of smaller switches  exploiting parallelism: fragment datagram into fixed length cells on entry switch cells through the fabric, reassemble datagram at exit 8x8 multistage switch built from smaller-sized switches Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-27 Switching via interconnection network  scaling, using multiple switching “planes” in parallel:  speedup, scaleup via parallelism  Cisco CRS router: fabric plane 0  basic unit: 8 fabric plane 1 fabric plane 2 switching planes............ fabric plane 3 fabric plane 4  each plane: 3-stage............ fabric plane 5 interconnection fabric plane 6............ fabric plane 7 network............  up to 100’s Tbps switching capacity Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-28 Input port queuing  If switch fabric slower than input ports combined -> queueing may occur at input queues queueing delay and loss due to input buffer overflow!  Head-of-the-Line (HOL) blocking: queued datagram at front of queue prevents others in queue from moving forward switch switch fabric fabric output port contention: only one red one packet time later: green datagram can be transferred. lower red packet experiences HOL blocking packet is blocked Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-29 Output port queuing datagram This is a really important slide switch buffer link layer line fabric termination protocol (rate: NR) queueing (send) R  Buffering required when datagrams arrive from fabric faster than link Datagrams can be lost transmission rate. Drop policy: which due to congestion, lack of datagrams to drop if no free buffers? buffers  Scheduling discipline chooses Priority scheduling – who among queued datagrams for gets best performance, transmission network neutrality Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-30 Output port queuing switch switch fabric fabric at t, packets more one packet time later from input to output  buffering when arrival rate via switch exceeds output line speed  queueing (delay) and loss due to output port buffer overflow! Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-31 How much buffering?  RFC 3439 rule of thumb: average buffering equal to “typical” RTT (say 250 msec) times link capacity C e.g., C = 10 Gbps link: 2.5 Gbit buffer  more recent recommendation: with N flows, buffering equal to RTT. C N  but too much buffering can increase delays (particularly in home routers) long RTTs: poor performance for realtime apps, sluggish TCP response recall delay-based congestion control: “keep bottleneck link just full enough (busy) but no fuller” Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-32  Buffer Management buffer management: switch datagram buffer link  drop: which packet to add, fabric layer line R drop when buffers are full protocol queueing (send) termination tail drop: drop arriving scheduling packet priority: drop/remove on priority basis Abstraction: queue  marking: which packets to mark to signal congestion R packet departures (ECN, RED) packet arrivals queue link (waiting area) (server) Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-33 Packet Scheduling: FCFS packet scheduling: deciding FCFS: packets transmitted in which packet to send next on order of arrival to output link port first come, first served priority  also known as: First-in-first- round robin out (FIFO) weighted fair queueing  real world examples? Abstraction: queue R packet departures packet arrivals queue link (waiting area) (server) Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-34 Scheduling policies: priority Priority scheduling: high priority queue  arriving traffic classified, arrivals queued by class classify link departures any header fields can be low priority queue used for classification 2  send packet from highest arrivals 1 3 4 5 priority queue that has packet buffered packets in service 1 3 2 4 5 FCFS within priority class departures 1 3 2 4 5 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-35 Scheduling policies: round robin Round Robin (RR) scheduling: arriving traffic classified, queued by class any header fields can be used for classification R server cyclically, repeatedly scans class queues, classify link departures sending one complete arrivals packet from each class (if available) in turn Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-36 Scheduling policies: weighted fair queueing Weighted Fair Queuing (WFQ):  generalized Round Robin  each class, i, has weight, wi, w1 and gets weighted amount of service in each cycle: w2 R wi classify link departures Σjwj arrivals w3  minimum bandwidth guarantee (per-traffic-class) Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-37 Sidebar: Network Neutrality What is network neutrality?  technical: how an ISP should share/allocation its resources packet scheduling, buffer management are the mechanisms  social, economic principles protecting free speech encouraging innovation, competition  enforced legal rules and policies Different countries have different “takes” on network neutrality Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-38 Sidebar: Network Neutrality 2015 US FCC Order on Protecting and Promoting an Open Internet: three “clear, bright line” rules: no blocking … “shall not block lawful content, applications, services, or non-harmful devices, subject to reasonable network management.” no throttling … “shall not impair or degrade lawful Internet traffic on the basis of Internet content, application, or service, or use of a non-harmful device, subject to reasonable network management.” no paid prioritization. … “shall not engage in paid prioritization” Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-39 ISP: telecommunications or information service? Is an ISP a “telecommunications service” or an “information service” provider?  the answer really matters from a regulatory standpoint! US Telecommunication Act of 1934 and 1996: Title II: imposes “common carrier duties” on telecommunications services: reasonable rates, non-discrimination and requires regulation Title I: applies to information services: no common carrier duties (not regulated) but grants FCC authority “… as may be necessary in the execution of its functions” 4 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-40 Network layer: “data plane” roadmap  Network layer: overview data plane control plane  What’s inside a router input ports, switching, output ports buffer management, scheduling  IP: the Internet Protocol  Generalized Forwarding, SDN datagram format match+action addressing OpenFlow: match+action in action network address translation IPv6 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-41 Network Layer: Internet host, router network layer functions: transport layer: TCP, UDP IP protocol Path-selection datagram format algorithms: addressing network implemented in packet handling conventions forwarding layer routing protocols (OSPF, BGP) table ICMP protocol SDN controller error reporting router “signaling” link layer physical layer Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-42  IP Datagram format Maximum length: 64K bytes 32 bits Typically: 1500 bytes or less IP protocol version number type of total datagram ver head. length length (bytes) header length(bytes) len service fragment fragmentation/ “type” of service: 16-bit identifier flgs  diffserv (0:5) offset reassembly time to upper header  ECN (6:7) header checksum live layer checksum TTL: remaining max hops source IP address 32-bit source IP address (decremented at each router) destination IP address 32-bit destination IP address upper layer protocol (e.g., TCP or UDP) options (if any) e.g., timestamp, record overhead route taken  20 bytes of TCP payload data  20 bytes of IP (variable length,  = 40 bytes + app typically a TCP layer overhead for or UDP segment) TCP+IP Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-43 IP addressing: introduction 223.1.1.1  IP address: 32-bit identifier 223.1.2.1 associated with each host or 223.1.1.2 router interface 223.1.1.4 223.1.2.9  interface: connection between 223.1.1.3 223.1.3.27 host/router and physical link 223.1.2.2 router’s typically have multiple interfaces 223.1.3.1 223.1.3.2 host typically has one or two interfaces (e.g., wired Ethernet, wireless 802.11) dotted-decimal IP address notation: 223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-44 IP addressing: introduction 223.1.1.1  IP address: 32-bit identifier 223.1.2.1 associated with each host or 223.1.1.2 router interface 223.1.1.4 223.1.2.9  interface: connection between 223.1.1.3 223.1.3.27 host/router and physical link 223.1.2.2 router’s typically have multiple interfaces 223.1.3.1 223.1.3.2 host typically has one or two interfaces (e.g., wired Ethernet, wireless 802.11) dotted-decimal IP address notation: 223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-45 IP addressing: introduction 223.1.1.1 Q: how are interfaces 223.1.2.1 actually connected? 223.1.1.2 A: we’ll learn about A: wired 223.1.1.4 223.1.2.9 that in chapters 6, 7 Ethernet interfaces connected by 223.1.1.3 223.1.3.27 223.1.2.2 Ethernet switches 223.1.3.1 223.1.3.2 For now: don’t need to worry about how one interface is connected to another (with no intervening router) A: wireless WiFi interfaces connected by WiFi base station Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-46 Subnets 223.1.1.1  What’s a subnet ? 223.1.2.1 device interfaces that can 223.1.1.2 223.1.1.4 223.1.2.9 physically reach each other without passing through an 223.1.1.3 223.1.3.27 intervening router 223.1.2.2  IP addresses have structure: subnet part: devices in same subnet 223.1.3.1 223.1.3.2 have common high order bits host part: remaining low order bits network consisting of 3 subnets Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-47 Subnets subnet 223.1.1.0/24 223.1.1.1 subnet 223.1.2.0/24 Recipe for defining subnets: 223.1.2.1 detach each interface from its 223.1.1.2 223.1.1.4 223.1.2.9 host or router, creating “islands” of isolated networks 223.1.1.3 223.1.3.27 223.1.2.2 each isolated network is subnet called a subnet 223.1.3.0/24 223.1.3.1 223.1.3.2 subnet mask: /24 (high-order 24 bits: subnet part of IP address) Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-48 Subnets 223.1.1.2 subnet 223.1.1/24 223.1.1.1  where are the 223.1.1.4 subnets? 223.1.1.3  what are the 223.1.9.2 223.1.7.0 /24 subnet subnet 223.1.9/24 subnet 223.1.7/24 addresses? 223.1.9.1 223.1.7.1 223.1.8.1 223.1.8.0 subnet 223.1.2/24 223.1.2.6 subnet 223.1.8/24 223.1.3.27 subnet 223.1.3/24 223.1.2.1 223.1.2.2 223.1.3.1 223.1.3.2 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-49 IP addressing: CIDR CIDR: Classless InterDomain Routing (pronounced “cider”) subnet portion of address of arbitrary length address format: a.b.c.d/x, where x is # bits in subnet portion of address subnet host part part 11001000 00010111 00010000 00000000 200.23.16.0/23 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-50 IP addresses: how to get one? That’s actually two questions: 1. Q: How does a host get IP address within its network (host part of address)? 2. Q: How does a network get IP address for itself (network part of address) How does host get IP address?  hard-coded by sysadmin in config file (e.g., /etc/rc.config in UNIX)  DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server “plug-and-play” Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-51 DHCP: Dynamic Host Configuration Protocol goal: host dynamically obtains IP address from network server when it “joins” network  can renew its lease on address in use  allows reuse of addresses (only hold address while connected/on)  support for mobile users who join/leave network DHCP overview:  host broadcasts DHCP discover msg [optional]  DHCP server responds with DHCP offer msg [optional]  host requests IP address: DHCP request msg  DHCP server sends address: DHCP ack msg Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-52 DHCP client-server scenario Typically, DHCP server will be co- DHCP server located in router, serving all subnets 223.1.1.1 223.1.2.1 to which router is attached 223.1.2.5 223.1.1.2 223.1.1.4 223.1.2.9 223.1.1.3 223.1.3.27 arriving DHCP client needs 223.1.2.2 address in this network 223.1.3.1 223.1.3.2 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-53 DHCP client-server scenario DHCP server: 223.1.2.5 DHCP discover Arriving client src : 0.0.0.0, 68 dest.: 255.255.255.255,67 Broadcast: is there a yiaddr: 0.0.0.0 transaction ID: 654 DHCP server out there? Broadcast: I’m a DHCP DHCP offer server! Here’s an IP src: 223.1.2.5, 67 dest: 255.255.255.255, 68 address you can use yiaddrr: 223.1.2.4 transaction ID: 654 lifetime: 3600 secs DHCP request The two steps above can be src: 0.0.0.0, 68 skipped “if a client remembers dest:: 255.255.255.255, 67 yiaddrr: 223.1.2.4 and wishes to reuse a previously transaction ID: 655 allocated network address” lifetime: 3600 secs Broadcast: OK. I would DHCP ACK like to use this IP address! Broadcast: OK. You’ve src: 223.1.2.5, 67 dest: 255.255.255.255, 68 got that IP address! yiaddrr: 223.1.2.4 transaction ID: 655 lifetime: 3600 secs Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-54 DHCP: more than IP addresses DHCP can return more than just allocated IP address on subnet:  address of first-hop router for client  name and IP address of DNS sever  network mask (indicating network versus host portion of address) Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-55 DHCP: example DHCP DHCP  Connecting laptop will use DHCP UDP DHCP DHCP IP to get IP address, address of first- DHCP Eth hop router, address of DNS server. Phy  DHCP REQUEST message encapsulated DHCP in UDP, encapsulated in IP, encapsulated DHCP DHCP 168.1.1.1 in Ethernet DHCP UDP IP  Ethernet frame broadcast (dest: DHCP DHCP Eth router with DHCP Phy server built into FFFFFFFFFFFF) on LAN, received at router router running DHCP server  Ethernet demux’ed to IP demux’ed, UDP demux’ed to DHCP Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-56 DHCP: example DHCP DHCP  DCP server formulates DHCP ACK DHCP UDP containing client’s IP address, IP DHCP IP address of first-hop router for client, Eth name & IP address of DNS server DHCP Phy  encapsulated DHCP server reply DHCP DHCP forwarded to client, demuxing up to UDP DHCP DHCP IP DHCP at client DHCP Eth router with DHCP DHCP Phy server built into  client now knows its IP address, name router and IP address of DNS server, IP address of its first-hop router Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-57 IP addresses: how to get one? Q: how does network get subnet part of IP address? A: gets allocated portion of its provider ISP’s address space ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/20 ISP can then allocate out its address space in 8 blocks: Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23 Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23 Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23... ….. …. …. Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-58 Hierarchical addressing: route aggregation hierarchical addressing allows efficient advertisement of routing information: Organization 0 200.23.16.0/23 Organization 1 “Send me anything 200.23.18.0/23 with addresses Organization 2 beginning 200.23.20.0/23. Fly-By-Night-ISP 200.23.16.0/20”... Internet. Organization 7. 200.23.30.0/23 “Send me anything ISPs-R-Us with addresses beginning 199.31.0.0/16” Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-59 Hierarchical addressing: more specific routes  Organization 1 moves from Fly-By-Night-ISP to ISPs-R-Us  ISPs-R-Us now advertises a more specific route to Organization 1 Organization 0 200.23.16.0/23 Organization 1 “Send me anything 200.23.18.0/23 with addresses Organization 2 beginning 200.23.20.0/23. Fly-By-Night-ISP 200.23.16.0/20”... Internet. Organization 7. 200.23.30.0/23 “Send me anything ISPs-R-Us with addresses Organization 1 beginning 199.31.0.0/16” 200.23.18.0/23 “or 200.23.18.0/23” Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-60 Hierarchical addressing: more specific routes  Organization 1 moves from Fly-By-Night-ISP to ISPs-R-Us  ISPs-R-Us now advertises a more specific route to Organization 1 Organization 0 200.23.16.0/23 “Send me anything with addresses Organization 2 beginning 200.23.20.0/23. Fly-By-Night-ISP 200.23.16.0/20”... Internet. Organization 7. 200.23.30.0/23 “Send me anything ISPs-R-Us with addresses Organization 1 beginning 199.31.0.0/16” 200.23.18.0/23 “or 200.23.18.0/23” Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-61 IP addressing: last words... Q: how does an ISP get block of Q: are there enough 32-bit IP addresses? addresses? A: ICANN: Internet Corporation for  ICANN allocated last chunk of Assigned Names and Numbers IPv4 addresses to RRs in 2011 http://www.icann.org/  NAT (next) helps IPv4 address allocates IP addresses, through 5 space exhaustion regional registries (RRs) (who may then allocate to local registries)  IPv6 has 128-bit address space manages DNS root zone, including delegation of individual TLD (.com,.edu , …) management Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-62 Network layer: “data plane” roadmap  Network layer: overview data plane control plane  What’s inside a router input ports, switching, output ports buffer management, scheduling  IP: the Internet Protocol  Generalized Forwarding, SDN datagram format match+action addressing OpenFlow: match+action in action network address translation IPv6 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-63 NAT: network address translation NAT: all devices in local network share just one IPv4 address as far as outside world is concerned rest of local network (e.g., home Internet network) 10.0.0/24 10.0.0.1 138.76.29.7 10.0.0.4 10.0.0.2 10.0.0.3 all datagrams leaving local network have datagrams with source or destination in same source NAT IP address: 138.76.29.7, this network have 10.0.0/24 address for but different source port numbers source, destination (as usual) Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-64 NAT: network address translation  all devices in local network have 32-bit addresses in a “private” IP address space (10/8, 172.16/12, 192.168/16 prefixes) that can only be used in local network  advantages:  just one IP address needed from provider ISP for all devices  can change addresses of host in local network without notifying outside world  can change ISP without changing addresses of devices in local network  security: devices inside local net not directly addressable, visible by outside world Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-65 NAT: network address translation implementation: NAT router must (transparently):  outgoing datagrams: replace (source IP address, port #) of every outgoing datagram to (NAT IP address, new port #) remote clients/servers will respond using (NAT IP address, new port #) as destination address  remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair  incoming datagrams: replace (NAT IP address, new port #) in destination fields of every incoming datagram with corresponding (source IP address, port #) stored in NAT table Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-66  NAT: network address translation NAT translation table 2: NAT router changes 1: host 10.0.0.1 sends WAN side addr LAN side addr datagram to datagram source address from 10.0.0.1, 3345 to 138.76.29.7, 5001 10.0.0.1, 3345 128.119.40.186, 80 138.76.29.7, 5001, …… …… updates table S: 10.0.0.1, 3345 D: 128.119.40.186, 80 10.0.0.1 1 S: 138.76.29.7, 5001 2 D: 128.119.40.186, 80 10.0.0.4 10.0.0.2 138.76.29.7 S: 128.119.40.186, 80 D: 10.0.0.1, 3345 4 S: 128.119.40.186, 80 10.0.0.3 D: 138.76.29.7, 5001 3 3: reply arrives, destination address: 138.76.29.7, 5001 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-67 NAT: network address translation  NAT has been controversial: routers “should” only process up to layer 3 address “shortage” should be solved by IPv6 violates end-to-end argument (port # manipulation by network-layer device) NAT traversal: what if client wants to connect to server behind NAT?  but NAT is here to stay: extensively used in home and institutional nets, 4G/5G cellular nets Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-68 IPv6: motivation  initial motivation: 32-bit IPv4 address space would be completely allocated  additional motivation: speed processing/forwarding: 40-byte fixed length header enable different network-layer treatment of “flows” Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-69 IPv6 datagram format flow label: identify priority: identify 32 bits datagrams in same priority among ver pri flow label "flow.” (concept of datagrams in flow payload len next hdr hop limit “flow” not well defined). source address 128-bit (128 bits) IPv6 addresses destination address (128 bits) payload (data) What’s missing (compared with IPv4):  no checksum (to speed processing at routers)  no fragmentation/reassembly  no options (available as upper-layer, next-header protocol at router) Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-70 Transition from IPv4 to IPv6  not all routers can be upgraded simultaneously no “flag days” how will network operate with mixed IPv4 and IPv6 routers?  tunneling: IPv6 datagram carried as payload in IPv4 datagram among IPv4 routers (“packet within a packet”) tunneling used extensively in other contexts (4G/5G) IPv4 header fields IPv6 header fields IPv4 payload IPv4 source, dest addr IPv6 source dest addr UDP/TCP payload IPv6 datagram IPv4 datagram Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-71 Tunneling and encapsulation A B Ethernet connects two E F Ethernet connecting IPv6 routers two IPv6 routers: IPv6 IPv6 IPv6 IPv6 IPv6 datagram Link-layer frame The usual: datagram as payload in link-layer frame IPv4 network A B E F connecting two IPv6 routers IPv6 IPv6/v4 IPv6/v4 IPv6 IPv4 network Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-72 Tunneling and encapsulation A B Ethernet connects two E F Ethernet connecting IPv6 routers two IPv6 routers: IPv6 IPv6 IPv6 IPv6 IPv6 datagram Link-layer frame The usual: datagram as payload in link-layer frame IPv4 tunnel A B IPv4 tunnel E F connecting IPv6 routers connecting two IPv6 routers IPv6 IPv6/v4 IPv6/v4 IPv6 IPv6 datagram IPv4 datagram tunneling: IPv6 datagram as payload in a IPv4 datagram Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-73 Tunneling A B IPv4 tunnel E F connecting IPv6 routers logical view: IPv6 IPv6/v4 IPv6/v4 IPv6 A B C D E F physical view: IPv6 IPv6/v4 IPv4 IPv4 IPv6/v4 IPv6 flow: X src:B src:B src:B flow: X src: A dest: E dest: E src: A dest: F dest: E dest: F Flow: X Flow: X Flow: X Src: A Src: A Src: A Note source and data Dest: F Dest: F Dest: F data destination addresses! data data data A-to-B: E-to-F: B-to-C: B-to-C: B-to-C: IPv6 IPv6 IPv6 inside IPv6 inside IPv6 inside IPv4 IPv4 IPv4 Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-74 IPv6: adoption  Google1: ~ 30% of clients access services via IPv6  NIST: 1/3 of all US government domains are IPv6 capable 1 https://www.google.com/intl /en/ipv6/statistics.html Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-75 IPv6: adoption  Google1: ~ 30% of clients access services via IPv6  NIST: 1/3 of all US government domains are IPv6 capable  Long (long!) time for deployment, use 25 years and counting! think of application-level changes in last 25 years: WWW, social media, streaming media, gaming, telepresence, … Why? 1 https://www.google.com/intl/en/ipv6/statistics.html Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-76 Chapter 4: done!  Network layer: overview  What’s inside a router  IP: the Internet Protocol Question: how are forwarding tables (destination-based forwarding) or flow tables (generalized forwarding) computed? Answer: by the control plane (next chapter) Copyrights ©Dr. Ehab Abousaif – Network Layer: 4-77