Chapter 4: outline 4.1 Overview of Network 4.4 Generalized - PDF document

Chapter 4: outline 4.1 Overview of Network 4.4 Generalized Forwarding layer and SDN  data plane  match  control plane t l l  action 4.2 What ’ s inside a  OpenFlow examples of match-plus-action router 4.3 IP: Internet Protocol  IPv4 datagram format  fragmentation  v4 addressing  network address translation  IPv6 11/2/2017 4-1 Network Layer: Data Plane (SSL) Network layer  delivers segments from sending to receiving host application transport network  sender encapsulates segments data link physical into datagrams network network data link data link data link data link network  Receiver de-encapsulates and physical physical data link physical delivers segments to network network data link data link transport layer physical physical  network layer in every host, network network data link data link every router physical physical network data link physical  router examines IP header application transport network field in every passing fi ld i i network network data link d li k network data link physical network data link datagram (exception: routers physical data link physical physical running MPLS) 11/2/2017 Network Layer: Data Plane 4-2 (SSL) 1

Key Network-Layer Functions  forwarding: move a packet from router’s input interface to an appropriate output i t interface f  routing: determine route taken by packets from source to destination  routing protocols ( intra-AS and inter-AS ) ti t ls ( i t AS d i t AS ) where AS is acronym for “Autonomous System”  every AS runs the same inter-AS protocol 11/2/2017 Network Layer: Data Plane 4-3 (SSL) Virtual-circuit networks need 3 rd function  Before datagrams can flow, end hosts and routers between them establish a virtual circuit circuit  Routers maintain state info  Earlier networks designed initially to compete with IP: ATM, frame relay, X.25 (from old to very old)  MPLS protocol designed about 10 years ago to provide virtual circuits supported by IP routers provide virtual circuits supported by IP routers (typically within the same AS); it borrows the idea of “labels” from ATM and frame relay  Today, such virtual circuits may serve as virtual links in Internet 11/2/2017 Network Layer: Data Plane 4-4 (SSL) 2

Network layer service models: Guarantees? Network Service Congestion Bandwidth loss Order Timing Architecture Model feedback none no no Internet best effort no no (TCP infers via loss) constant ATM CBR yes yes yes no rate congestion guaranteed ATM VBR yes yes yes no rate congestion g guaranteed no yes y ATM ABR no yes yes minimum none no yes ATM UBR no no 11/2/2017 Network Layer: Data Plane 4-5 (SSL) Origins of datagram and VC Internet (datagram) ATM (VC)  data exchange between  evolved from telephony computers  human conversation:  “elastic” service, no strict “ l ti ” i t i t  strict timing, loss timing requirement requirements  many link types  need for guaranteed  different characteristics services  uniform service difficult  “dumb” end systems  “smart” end systems  telephones (computers) ( p )  complexity inside  complexity inside  can adapt, perform network control, error recovery  simplicity inside network, complexity at “edge” 11/2/2017 Network Layer: Data Plane 4-6 (SSL) 3

Network layer: data plane, control plane Data plane Control plane  local, per-router  network-wide logic function function  determines how datagram is  determines how datagram is routed among routers along  determines how end-end path from source datagram arriving on an host to destination host input port is forwarded  main approach: to an output port  routing protocols implemented in routers values in arriving  new approach  new approach packet header  software-defined networking (SDN) : 1 0111 2 implemented in logically 3 centralized server(s) 11/2/2017 Network Layer: Data Plane 4-7 (SSL) Per-router control plane (more in Chapter 5) Individual routing process in every router. They interact by exchanging routing protocol messages Routing Algorithm control plane data plane values in arriving packet header 0111 1 2 3 11/2/2017 Network Layer: Data Plane 4-8 (SSL) 4

Logically centralized control plane (more in Chapter 5) A distinct (typically remote) controller interacts with local control agents (CAs). The controller computes routes. Remote Controller control plane data plane CA CA CA CA CA values in arriving packet header 0111 1 2 3 11/2/2017 Network Layer: Data Plane 4-9 (SSL) Chapter 4: outline 4.1 Overview of Network 4.4 Generalized Forwarding layer and SDN  data plane  match  control plane t l l  action 4.2 What ’ s inside a  OpenFlow examples of match-plus-action router 4.3 IP: Internet Protocol  datagram format  fragmentation  v4 addressing  network address translation  IPv6 11/2/2017 4-10 Network Layer: Data Plane (SSL) 5

Router architecture overview forwarding tables routing, management computed, then pushed routing control plane (software) to input ports processor forwarding data plane (hardware) high-speed input ports switching output ports fabric Physical Physical buffering queueing and Link layer layer and table Link packet layer layer lookup scheduling 11/2/2017 4-11 Network Layer: Data Plane (SSL) IPv4 addressing: CIDR Classful addressing (now obsolete): fixed-length subnet portion of 8, 16 or 24 bits CIDR: Classless InterDomain Routing m subnet portion of address of variable length m address format: a.b.c.d/x, where x is # bits in subnet portion of address host subnet part part part t 11001000 00010111 00010000 00000000 200.23.16.0/23 11/2/2017 Network Layer: Data Plane 4-12 (SSL) 6

Datagram networks  IPv4  no network-level concept of “connection” or “flow”  each packet forwarded independently using destination host address destination host address  packets between same source-dest pair may take different paths application application transport transport network network t k data link 1. Send data 2. Receive data data link physical physical 11/2/2017 Network Layer: Data Plane 4-13 (SSL) 4 billion Forwarding table possible entries Destination Address Range Link Interface 11001000 00010111 00010000 00000000 through 0 11001000 00010111 00010111 11111111 11001000 00010111 00011000 00000000 through 1 11001000 00010111 00011000 11111111 11001000 00010111 00011000 00000000 11001000 00010111 00011000 00000000 through 2 11001000 00010111 00011111 11111111 otherwise 3 11/2/2017 Network Layer: Data Plane 4-14 (SSL) 7

Longest prefix match Prefix Link Interface 11001000 00010111 00010 0 11001000 00010111 00011000 1 11001000 00010111 00011 2 otherwise 3 Examples Which interface? DA: 11001000 00010111 00010110 10100001 D DA: 11001000 00010111 00011000 10101010 Which interface? Whi h int f ? A forwarding table in an Internet core router has more than 400,000 IP prefixes (from 2014 data) Fast implementation uses Ternary Content Addressable Memory (TCAM), prefixes sorted in decreasing order (in length) 11/2/2017 Network Layer: Data Plane 4-15 (SSL) Virtual circuits: signaling protocols  used to set up, maintain, tear down VC  not used in Internet’s network layer, but may be used underneath the IP layer to provide a virtual used underneath the IP layer to provide a virtual link (e.g., MPLS tunnel) application application 6. Receive data transport 5. Data flow begins transport network 4. Call connected 3. Accept call network data link data link 1 Initiate call 1. Initiate call 2 i 2. incoming call i ll data link physical physical 11/2/2017 Network Layer: Data Plane 4-16 (SSL) 8

Virtual circuit (VC)  call setup, teardown for each call before data can flow  each packet carries a VC identifier which  each packet carries a VC identifier which  is fixed length and short  only needs to be unique for a link  is carried in an additional header inserted between link and network layer headers (called layer 2½)  every router on source-dest path maintains state  every router on source-dest path maintains state information for each passing VC  incoming and outgoing VC identifiers,  resources allocated to VC (bandwidth, buffers) 11/2/2017 Network Layer: Data Plane 4-17 (SSL) VC Forwarding table VC number 12 22 32 3 1 2 Forwarding table in northwest router: interface number Incoming interface Incoming VC # Outgoing interface Outgoing VC # 1 12 3 22 2 63 1 18 3 7 2 17 1 97 3 87 … … … …  Forwarding is fast because short fixed-length VC numbers are used vs. IP forwarding table with variable-length prefixes. (This is not forwarding in IP layer but it is considered to be in data plane.)  May have additional state information about service guarantees 11/2/2017 Network Layer: Data Plane 4-18 (SSL) 9