Performance Enhancement of TFRC in Wireless Networks

Performance Enhancement of TFRC in Wireless Networks

Network Layer Computer Networks Spring 2012 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP

NAT 4.5 Routing algorithms Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 2

Network Layer Introduction Concerned with getting packets from source to destination. The network layer must know the topology of the subnet and choose appropriate paths through it. When source and destination hosts are in different networks, the network layer (IP) must deal with these differences. Key issue: What service does the network layer provide to the transport layer? connection-oriented or Computer Networks Network Layer 3 Network Layer Design Goals 1. The services provided by the network layer should be independent of the subnet topology. 2. The Transport Layer should be shielded from the number, type and

topology of the subnets present. 3. The network addresses available to the Transport Layer should use a uniform numbering plan (even across LANs and WANs). Computer Networks Network Layer 4 Network Layer Messages Messages Segments Transport layer Transport layer Network service Network service Network layer End systemData link layer a Physical layer

Network layer Network layer Data link layer Network layer Data link layer Data linkEnd system layer b Physical layer Physical layer Physical layer Leon-Garcia & Widjaja: Communication Networks Computer Networks Network Layer

5 Network Layer Machine A Machine B Application Application Transport Router/Gateway Internet Internet Network Interface Transport Internet Network Interface Network Interface Network 1

Network 2 Leon-Garcia & Widjaja: Communication Networks Computer Networks Network Layer 6 Metropolitan Area Network (MAN) Organization Servers Gatewa y To the Internet or wide area network s Backbon e R R Departmental Server

R s R S S S R R s s s s s s s s s Leon-Garcia & Widjaja: Communication Networks Computer Networks

Network Layer 7 Wide Area Network (WAN) Interdomain level Border routers Autonomous system or domain Border routers Internet Service Provider (ISP) LAN level Leon-Garcia & Widjaja: Communication Networks Intradomain level Computer Networks Network Layer 8

Modern Internet Backbone National service provider A National service provider B NAP NAP National service provider C Network Access Point National Internet Service Providers Leon-Garcia & Widjaja: Communication Networks Computer Networks Network Layer 9 Network Access Point NAP RA Route server RB LAN RC

Leon-Garcia & Widjaja: Communication Networks Computer Networks Network Layer 10 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol

Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP

4.7 Broadcast and multicast routing Computer Networks Network Layer K&R 11 Datagram Packet Switching Packet 1 Packet 1 Packet 2 Packet 2 Packet 2 Leon-Garcia & Widjaja: Communication Networks Computer Networks Network Layer 12 Datagram Routing Table Destination address Output port

0785 7 1345 12 1566 6 2458 12 IP addresses Leon-Garcia & Widjaja: Communication Networks Computer Networks Network Layer 13 Virtual Circuit Packet Switching Packet Packet

Leon-Garcia & Widjaja: Communication Networks Computer Networks Network Layer 14 Virtual Circuit Routing Table Entry for packets with identifier 15 Identifier Output port Next identifier 12 13 44 15 9

23 27 13 16 58 7 34 Packet leaves with new identifier 23 Leon-Garcia & Widjaja: Communication Networks Computer Networks Network Layer 15 Network Layer

transport segment from sending to receiving host. on sending side, encapsulates segments into datagram packets. on receiving side, delivers segments to transport layer. network layer protocols in every host, router. router examines Computer header fields in allNetworks IP applicatio n transport network data link physical

network data link physical network data link physical network data link physical network data link physical network data link physical network network data link data link physical physical network data link physical network data link physical

network data link physical network data link physical applicatio n transport network data link physical K&R Network Layer 16 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit

and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms Algorithm Classification

Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 17 Two Key Network Layer Functions forwarding: move packets from routers input to appropriate router output. routing: determine route

taken by packets from source to destination. analogy: forwarding: process of getting through single interchange routing: process of planning trip from source to destination K & R Computer Networks Network Layer 18 Interplay between Routing and Forwarding routing algorithm local forwarding table header value output link 0100 0101 0111 1001

3 2 2 1 value in arriving packets header 0111 1 3 2 K&R Computer Networks Network Layer 19 Router Node node 15 packet packet Incoming Link 17 Outgoing Link Router Link Buffer Server

Computer Networks Network Layer 20 Routing in an internet Figure 3.14 A Simple internetwork with Three Routers Computer Networks Network Layer 21 Protocol Layers along the Route IP runs on all the nodes in a collection of networks and defines the infrastructure that allows these nodes and networks to function as a single logical internetwork. Figure 3.15 Protocol Layers used for a Simple internet Computer Networks Network Layer 22 Forwarding Table Example Table 3.6 Complete Forwarding Table for Router R2 in Figure 3.14 Network Number Next Hop

1 R1 2 Interface 1 3 Interface 0 4 R3 Note As R2 is on Network 2 and Network 3, this table shows packets headed for H1, H2 and H3 are not forwarded by R2 to another router. Computer Networks Network Layer 23 The Internet Network Layer Host, router network layer functions: Transport Layer: TCP, UDP Network Layer

Routing protocols path selection RIP, OSPF, BGP IP protocol addressing conventions datagram format packet handling conventions forwarding table ICMP protocol error reporting router signaling Data Link Layer Physical Layer K&R Computer Networks Network Layer 24 Network Layer Topics

4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms

Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 25 IP Datagram Format IP protocol version number header length (bytes) 32 bits ver head.type of len service

TOS:: data type TTL:: max hops remaining (each router decrements) upper layer protocol to deliver payload to how much overhead with TCP? 20 bytes of TCP 20 bytes of IP = 40 bytes + app layer overhead length fragment 16-bit identifier flgs offset time to upper header layer live checksum total datagram length (bytes) Three fields for fragmentation/ reassembly

32 bit source IP address 32 bit destination IP address Options (if any) data (variable length, typically a TCP or UDP segment) E.g. timestamp, record route taken, specify list of routers to visit. K&R Computer Networks Network Layer 26 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 Computer Networks Network Layer K&R 27 IP Fragmentation and Reassembly Specified in 8 byte units Figure 3.18 Header fields used in IP fragmentation: (a) unfragmented packet; (b) fragmented packets. Computer Networks Network Layer 28

IP Fragmentation for Figure 3.14 Figure 3.17 IP datagrams traversing the sequence of physical networks graphed in Figure 3.14. Computer Networks Network Layer 29 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol

Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 Broadcast and

multicast routing Computer Networks Network Layer K&R 30 Global Internet NSFNET backbone Stanford ISU BARRNET MidNet regional Westnet regional regional Berkeley PARC UNM

NCAR UNL KU UA Figure 4.1 The tree structure of the Internet in 1990 Computer Networks Network Layer 31 Global Internet Each provider network is regional and a single autonomous system (AS) Major issues are: Scalability of routing Address utilization Now out of IPv4 addresses Hierarchy is used to improve scalability. Namely, utilize subnets with masks.

Computer Networks Network Layer 32 IPv4 Network Classes Figure 3.19 IP addresses: (a) class A; (b) class B; (c) class C. Computer Networks Network Layer 33 Network Number Problems Assigning one network number per physical network uses up IP address too fast! Adding more network numbers also increases forwarding table size. Subnet solution :: The idea is to take a single IP network number and allocate the IP addresses with that network number to several physical networks which are referred to as subnets. The subnets need to be physically close to each other for routing Computer Networks Network Layer

34 Subnetting The mechanism by which a single network number can be shared among multiple networks involves configuring all the nodes on each subnet with a subnet mask. The subnet mask enables introduction of a single subnet number which provides for another level of hierarchy into the IP address. All hosts on a given subnet are configured with the same mask, i.e., there is one subnet mask per subnet. Computer Networks Network Layer 35 IP Addressing: Introduction IP address:: 32-bit

identifier for host, router interface. interface:: connection between host/router and physical link 223.1.1.1 223.1.1.2 223.1.1.4 223.1.1.3 223.1.3.1 223.1.2.1 223.1.2.9 223.1.3.27 223.1.2.2 223.1.3.2 routers typically have multiple interfaces. host typically has one 223.1.1.1 = 11011111 00000001 00000001 00000001 interface. IP addresses are 223 1

1 1 K&R associated with each interface. Computer Networks Network Layer 36 Subnets IP address: subnet part (high order bits) host part (low order bits) What is a subnet ? device interfaces with same subnet part of IP address. can physically reach each other without intervening router. K&R 223.1.1.1 223.1.1.2 223.1.1.4 223.1.1.3

223.1.2.1 223.1.2.9 223.1.3.27 223.1.2.2 subnet 223.1.3.1 223.1.3.2 network consisting of three subnets Computer Networks Network Layer 37 Subnet Masks Figure 3.20 Subnet Addressing Computer Networks Network Layer 38 Subnets 223.1.1.0/24 Subnet Concepts 223.1.2.0/24 To determine the subnets, detach each

interface from its host or router, creating islands of isolated networks. Each isolated network is called a subnet. Sending host does bitwise AND between 223.1.3.0/24 subnet mask and destination address to Subnet mask: /24 :: K&R defined determine whether by Network the leftmost 24 bits. packet needs Computer to be Networks 39 Layer Subnets 223.1.1.2 How many? 223.1.1.1 223.1.1.4 223.1.1.3

223.1.9.2 223.1.7.0 223.1.9.1 223.1.7.1 223.1.8.1 223.1.8.0 223.1.2.6 K&R 223.1.2.1 223.1.3.27 223.1.2.2 223.1.3.1 Computer Networks Network Layer 223.1.3.2 40 IP Addressing: CIDR CIDR: Classless InterDomain Routing Allows a subnet portion of address of

arbitrary length. address format: a.b.c.d/x, where x is number of bits in subnet portion of address. subnet host part part 11001000 00010111 00010000 00000000 200.23.16.0/23 Computer Networks Network Layer K&R 41 Classless Routing (CIDR) CIDR helps aggregate routes by breaking up rigid boundaries between classes. Handing out Class C addresses in contiguous blocks by address, makes it possible for addresses to share a common prefix. allocate Class C networks as a power of 2. We need a protocol that understands these rules, e.g., BGP!! Network numbers are represented by (length,value) where length is the Networks Network Layer length of Computer the prefix

{similar to a 42 Classless Routing (CIDR) Corporation X (11000000000001000001) Border gateway (advertises path to 11000000000001) Regional network Corporation Y (11000000000001000000) Figure 4.27 Route Aggregation with CIDR P&D 4th Computer Networks Network Layer 43 CIDR Route Aggregation Eight ISP customers share a 21-bit common prefix. Figure 3.22 Route Aggregation with CIDR Computer Networks Network Layer

44 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT

4.5 Routing algorithms Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 45

Routing Algorithm Classification Computer Networks Network Layer Routing Routing algorithm:: that part of the Network Layer responsible for deciding on which output line to transmit an incoming packet. Remember: For virtual circuit subnets the routing decision is made ONLY at set up. Algorithm properties:: correctness, simplicity, robustness, stability, fairness, optimality, and scalability. Computer Networks Network Layer 47 Routing Classification Adaptive Routing based on current measurements of traffic and/or topology. 1. centralized 2. isolated

3. distributed Non-Adaptive Routing routing computed in advance and off-line 1. flooding 2. static routing using shortest path algorithms Computer Networks Network Layer 48 Flooding Pure flooding :: every incoming packet to a node is sent out on every outgoing line. Obvious adjustment do not send out on arriving link (assuming full-duplex links). The routing algorithm can use a hop counter (e.g., TTL) to dampen the flooding. Selective flooding :: only send on

those lines going approximately in the right direction. Computer Networks Network Layer 49 Routing is Graph Theory Problem edges have costs Figure 3.28 Network represented as a graph. Computer Networks Network Layer 50 Shortest Path Routing 1. Bellman-Ford Algorithm [Distance Vector] 2. Dijkstras Algorithm [Link State] What does it mean to be the shortest (or optimal) route? We need a cost metric (edges in graph): a. Minimize the number of hops along the path. b. Minimize the mean packet delay. c. Maximize theNetworks network throughput. Computer

Network Layer 51 Internetwork Routing [Halsall] Adaptive Routing Centralized [RCC] Distributed [IGP] Intradomain routing Interior Gateway Protocols Isolated Interdomain routing[EGP] [BGP,IDRP] Exterior Gateway Protoco Distance Vector routing Link State routing [RIP] [OSPF,IS-IS,PNNI] Computer Networks Network Layer

52 Adaptive Routing Design Design Issues: 1. How much overhead is incurred due to gathering the routing information and sending routing packets? 2. What is the time frame (i.e, the frequency) for sending routing packets in support of adaptive routing? 3. What is the complexity of the routing strategy? Computer Networks Network Layer 53 Adaptive Routing Basic functions: 1. Measurement of pertinent network data {e.g. the cost metric}. 2. Forwarding of information to where the routing computation will be done.

3. Compute the routing tables. 4. Convert the routing table information into a routing decision and then dispatch the data packet. Computer Networks Network Layer 54 Centralized Routing A W RCC B Z Computer Networks Network Layer 55 Network Layer Topics

4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms

Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 56 Distance Vector Routing {Tanenbaum & Perlman version} Computer Networks Network Layer Distance Vector Routing Historically known as the old ARPANET routing algorithm {or known as Bellman-Ford (BF)

algorithm}. BF Basic idea: each router maintains a Distance Vector table containing the distance between itself and ALL possible destination nodes. Distances, based on the chosen metric, are computed using information from the neighbors distance Computer vectors. Networks Network Layer 58 Distance Vector Routing 1. 2. Information kept by DV router each router has an ID associated with each link connected to a router, there is a link cost (static or dynamic). Distance Vector Table Initialization Distance to itself = 0 Distance to ALL other routers = infinity number Computer Networks Network Layer 59

Distance Vector Algorithm [Perlman] 1. 2. 3. A router transmits its distance vector to each of its neighbors in a routing packet. Each router receives and saves the most recently received distance vector from each of its neighbors. A router recalculates its distance vector when: a. It receives a distance vector from a neighbor containing different information than before. b. It discovers that a link to a neighbor has gone down (i.e., a topology change). The DV calculation is based on minimizing the cost to each Computer Networks Network Layer destination. 60 Distance Vector Example

Figure 5-9.(a) A subnet. (b) Input from A, I, H, K, and the new routing table for J. Tanenbaum Computer Networks Network Layer 61 Distance Vector Routing {Kurose & Ross version} Computer Networks Distance Vector Routing Distance Vector Algorithm Bellman-Ford Equation (dynamic programming) Define dx(y) := cost of least-cost path from x to y Then v dx(y) = min {c(x,v) + dv (y)} where min is taken over all neighbors v of x. Computer Networks Network Layer 63 Bellman-Ford Example

5 u 2 v 2 3 Clearly, dv(z) = 5, dx(z) = 3, dw(z) = 3 w 5 3 1 z B-F equation says: du(z) = min { c(u,v) + dv(z), 1 c(u,x) + dx(z), c(u,w) + dw(z) } = min {2 + 5, 1 + 3, The node that achieves minimum is next5 + 3} = 4 hop in shortest path forwarding table. Namely, packets from u destined for z are

forwarded out link between u and x. 1 x y 2 Computer Networks Network Layer 64 Distance Vector Algorithm (3) Dx(y) = estimate of least cost from x to y Node x knows cost to each neighbor v: c(x,v) Node x maintains distance vector Dx = [Dx(y): y N ] Node x also maintains its neighbors distance vectors For each neighbor v, x maintains

Dv = [Dv(y): y N ] Computer Networks Network Layer 65 Distance Vector Algorithm (4) DV Basic idea: From time-to-time, each node sends its own distance vector estimate to neighbors. Asynchronous When a node x receives a new DV estimate from any neighbor v, it saves vs distance vector and it updates its own DV using B-F equation: Dx(y) min {c(x,v) + Dv(y)} for each node y N v Under minor, natural conditions, the estimate Dx(y) converges to the actual least cost dx(y). Computer Networks Network Layer

66 Distance Vector Algorithm (5) Iterative, asynchronous: each local iteration caused by: local link cost change DV update message from neighbor Distributed: each node notifies neighbors only when its DV changes neighbors then notify their neighbors if necessary. Each node: wait for (change in local link cost or msg from neighbor) recompute estimates

if DV to any destination has changed, notify neighbors Computer Networks Network Layer 67 from x 0 2 7 y z node y table cost to x y z from Dx(y) = min{c(x,y) + Dy(y), c(x,z) + Dz(y)} Dx(z) = min{c(x,y) + Dy(z), c(x,z) + Dz(z)} = min{2+0 , 7+1} = 2 node x table = min{2+1 , 7+0} = 3 cost to cost to x y z x y z x 0 2 3 y 2 0 1 z 7 1 0 2

x y 2 0 1 z node z table cost to x y z from from x x y z 71 0 time Computer Networks Network Layer y 7 1 z 68

Dx(y) = min{c(x,y) + Dy(y), c(x,z) + Dz(y)}Dx(z) = min{c(x,y) + Dy(z), c(x,z) + Dz(z)} = min{2+0 , 7+1} = 2 node x table = min{2+1 , 7+0} = 3 x 0 2 7 y z node y table cost to x y z x 0 2 3 y 2 0 1 z 7 1 0 x 0 2 3 y 2 0 1 z 3 1 0 x 0 2 7 y 2 0 1 z 7 1 0 x 0 2 3 y 2 0 1 z 3 1 0 from from

cost to x y z x 0 2 7 y 2 0 1 z 3 1 0 2 x y 7 1 z cost to x y z from x y z 71 0 cost to x y z cost to x y z

from from from x y 2 0 1 z node z table cost to x y z from cost to x y z from cost to x y z from cost to x y z x 0 2 3 y 2 0 1

z 3 1 0 time Computer Networks Network Layer 69 Distance Vector: Link Cost Changes Link cost changes: node detects local link cost change. updates routing info, recalculates 1 y 4 1 x 50 z distance vector. At time t0, y detects the link-cost change, updates if DV changes, it notifies its DV, and informs its neighbors. neighbors

. good At time t1, z receives the update from y and updates its news table. travels It computes a new least cost to x and sends its neighbors its time DV. t2, y receives zs update and updates its distance At fast table. ys least costs do not change and hence y does not send any message to z. Computer Networks Network Layer 70 Distance Vector: Link Cost Changes Link cost changes: good news travels fast bad news travels slow - count to infinity problem! 44 iterations before algorithm stabilizes: see P&D page 248! 60 y 4 1

x 50 z Possible solutions: 1. Keep infinity small {depends on graph diameter}. 2. Split Horizon: node does not send those routes learned from a neighbor back to that neighbor. 3. Split Horizon with Poison Reverse: If Z routes through Y to get to X, Z tells Y its (Zs) distance to X is infinite (so Y wont route to X via Z). Does this solve count to infinity problem? Computer Networks Network Layer 71 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit

and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms Algorithm Classification

Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 72 Link State Algorithm 1. 2. 3. 4. Each router is responsible for meeting its neighbors and learning their names. Each router constructs a link state

packet (LSP) which consists of a list of names and cost to reach each of its neighbors. The LSP is transmitted to ALL other routers. Each router stores the most recently generated LSP from each other router. Each router uses complete information on the network topology to compute the shortest path route toLayer each Computer Networks Network 73 Reliable Flooding X A C B D X

A C B (a) X A C B (c) D (b) D X A C B D

(d) Figure 3.32 Reliable LSP Flooding Computer Networks Network Layer 74 Reliable Flooding The process of making sure all the nodes participating in the routing protocol get a copy of the link-state information from all the other nodes. LSP contains: Sending routers node ID List of connected neighbors with the associated link cost to each neighbor Sequence number Time-to-live (TTL) {an aging mechanism} Computer Networks Network Layer 75 Reliable Flooding First two items enable route calculation.

Last two items make process reliable ACKs and checking for duplicates is needed. Periodic Hello packets used to determine the demise of a neighbor. The sequence numbers are not expected to wrap around. Computer Networks Network Layer 76 A Link-State Routing Algorithm Notation: algorithm Dijkstras net topology, link costs known nodes c(x,y):

link cost from node x to to y; all = if not direct accomplished via link state broadcast. neighbors. allcurrent nodes have same D(v): value ofinfo. cost of path from source to computes least cost paths from one node (source) destination v to all other nodes p(v): predecessor node along path from source to v gives forwarding table for that node. N':

set of nodes whose least cost path is definitively iterative: after k iterations, know least cost path to k known. destinations. K&R Computer Networks Network Layer 77 Dijsktras Algorithm [K&R] 1 Initialization: 2 N' = {u} 3 for all nodes v 4 if v adjacent to u 5 then D(v) = c(u,v) 6 else D(v) = 7 8 Loop 9 find w not in N' such that D(w) is a minimum 10 add w to N' 11 update D(v) for all v adjacent to w and not in N' : 12 D(v) = min( D(v), D(w) + c(w,v) ) 13 /* new cost to v is either old cost to v or known 14 shortest path cost to w plus cost from w to v */ 15 until all nodes in N' K&R

Computer Networks Network Layer 78 Dijkstras Algorithm: Example Step 0 1 2 3 4 5 N' u ux uxy uxyv uxyvw uxyvwz D(v),p(v) D(w),p(w) 2,u 5,u 2,u 4,x 2,u 3,y 3,y D(x),p(x)

1,u D(y),p(y) 2,x D(z),p(z) 4,y 4,y 4,y 5 u 2 1 v 2 x 3 w 3 1 1

y 5 z 2 Computer Networks Network Layer K&R 79 Dijkstras Algorithm: Example (2) Resulting shortest-path tree from u: v w u z x y Resulting forwarding table in u: destination link v (u,v) x (u,x) y (u,x) w (u,x)

z (u,x) Computer Networks Network Layer K&R 80 Dijkstras Algorithm, Discussion Algorithm complexity: n nodes each iteration: need to check all nodes, w, not in N n(n+1)/2 comparisons: O(n2) more efficient implementations possible: O(nlogn) Oscillations possible: e.g., link cost = amount of carried traffic 1 A 1+e D B 0 0 0 C e 1 1 e

initially A 2+e 0 D 1+e1 B 0 C 0 recompute routing 0 A A 2+e D 00 B 1 C 1+e 2+e 0 D 1+e1 B 0 C e recompute recompute

Computer Networks Network Layer K&R 81 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 Whats inside a router 4.4 IP: Internet Protocol Datagram Format IPv4 addressing

Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer

K&R 82 Hierarchical Routing Our routing study thus far - idealization all routers identical network flat not true in practice scale: with 200 million destinations: cant store all destinations in routing tables! routing table exchange would swamp links! administrative autonomy internet = network of networks

each network admin may want to control routing in its own network Computer Networks Network Layer 83 Hierarchical Routing aggregate routers into regions, autonomous systems (AS) routers in same AS run same routing protocol Gateway router Direct link to router in another AS intra-AS routing protocol routers in different AS can run different intraAS routing protocol Computer Networks Network Layer

84 Interconnected ASs 3c 3a 3b AS3 2a 1c 1a 1d 1b AS1 Intra-AS Routing algorithm Inter-AS Routing algorithm Forwarding table 2c 2b

AS2 forwarding table configured by both intra- and inter-AS routing algorithm intra-AS sets entries for internal destinations. inter-AS & intra-AS sets entries for external destinations. Computer Networks Network Layer 85 Inter-AS Tasks suppose router in AS1 receives datagram destined outside of AS1: router should forward packet to gateway router, but which one?

AS1 must: 1. learn which dests are reachable through AS2, which through AS3 2. propagate this reachability info to all routers in AS1 Job of inter-AS routing! 3c 3a 3b AS3 2a 1c 1a 1d 1b AS1 2c 2b

AS2 Computer Networks Network Layer 86 Network Layer Topics 4. Introduction 4.51Routing algorithms Algorithm 4.2 VirtualClassification circuit Link State and datagram Distance Vector networks Hierarchical Routing 4.3 What is inside a

4.6 Routing in the Internet router? 4.4RIP IP: Internet OSPF Protocol BGP Datagram format 4.7 ICMP IPv4 addressing Subnets CIDR ARP & DHCP NAT Computer Networks Network Layer 87 Intra-AS Routing also known as Interior Gateway Protocols (IGP) most common Intra-AS routing protocols:

RIP: Routing Information Protocol OSPF: Open Shortest Path First IGRP: Interior Gateway Routing Protocol (Cisco proprietary) Computer Networks Network Layer 88 Network Layer Topics 4. Introduction 4.51Routing algorithms Algorithm 4.2 VirtualClassification circuit Link State and datagram Distance Vector networks

Hierarchical Routing 4.3 What is inside a 4.6 Routing in the Internet router? 4.4RIP IP: Internet OSPF Protocol BGP Datagram format 4.7 ICMP IPv4 addressing Subnets CIDR ARP & DHCP NAT Computer Networks Network Layer 89 Routing Information Protocol (RIP)

RIP had widespread use because it was distributed with BSD Unix in routed, a router management daemon in 1982. RIP - most used Distance Vector protocol. RFC1058 in June 1988 Runs over UDP. Metric = hop count BIG problem is max. hop count =16 RIP limited to running on small networks (or ASs that have a small Computer Networks Network Layer diameter)!! 90 Routing Information Protocol (RIP) u v A z

C B D w x y From router A to subnets: destination hops u 1 v 2 w 2 x 3 y 3 z 2 Sends DV packets every 30 seconds (or faster) as Response Messages (also called advertisements).

each advertisement: list of up to 25 destination subnets within AS. Upgraded to RIPv2 Computer Networks Network Layer 91 RIP Packets 0 8 Command 16 Version Family of net 1 31 Must be zero Address of net 1 Address of net 1 (network_address, distance) pairs Distance to net 1 Family of net 2

Address of net 2 Address of net 2 Distance to net 2 Figure 4.17 RIP Packet Format P&D 4th Computer Networks Network Layer 92 RIPv2 Packets subnet masks Figure 3.31 RIPv2 Packet Format Computer Networks Network Layer 93 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit

and datagram networks 4.3 Whats inside a router 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms Algorithm Classification

Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 94 OSPF (Open Shortest Path First) open :: publicly available (due to IETF) uses Link State algorithm LS packet dissemination topology map at each node route computation uses Dijkstras algorithm.

OSPF advertisement carries one entry per neighbor router. advertisements disseminated to entire AS (via flooding*). carried in OSPF messages directly over IP (rather than TCP or UDP). * However hierarchy (partitioning domains into areas) reduces flooding impact. Computer Networks Network Layer 95 Partitioning Domains Figure 4.2 A domain divided into areas Computer Networks Network Layer 96 Hierarchical OSPF Computer Networks Network Layer 97 Hierarchical OSPF Two-level Hierarchy:: local area,

backbone. Some Link-State Advertisement (LSA) types are only sent into one area. Each node has detailed area topology; only knows direction (shortest path) to nets in other areas. area border routers: summarize distances to nets in own area, advertise to other Area Border routers. backbone routers: run OSPF routing limited to backbone. boundary routers: connect to other ASs. Computer Networks Network Layer 98 OSPF LSA Types 1. Router link advertisement [Hello message] 2. Network link advertisement identifies connected networks. 3. Network summary link advertisement 4. AS border routers summary link

advertisement 5. AS external link advertisement Computer Networks Network Layer 99 OSPF Header Figure 3.34 OSPF Header Format Computer Networks Network Layer 100 Type 1 OSPF LSA Figure 3.3 OSPF Link-State Advertisement (LSA) Computer Networks Network Layer 101 OSPF Advanced Features (not in RIP)

security: all OSPF messages authenticated (to prevent malicious intrusion). multiple same-cost paths means distributed load balancing of traffic over routes (only one path in RIP). For each link, multiple cost metrics for different TOS (e.g., satellite link cost set low for best effort; high for real time). integrated uni- and multicast support: Multicast OSPF (MOSPF) uses same topology data base as OSPF. hierarchical OSPF is used in large domains. Computer Networks Network Layer 102 OSPF Figure 5-65.The relation between ASs, backbones, and areas in OSPFTanenbaum Computer Networks Network Layer 103 Network Layer Topics

4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP &DHCP NAT 4.5 Routing algorithms

Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 104 Internet Inter-AS Routing: BGP BGP (Border Gateway Protocol): de facto standard interdomain routing protocol.

BGP provides each AS a means to: 1. Obtain subnet reachability information from neighboring ASs. 2. Propagate reachability information to all ASinternal routers. 3. Determine good loop-free routes to subnets based on reachability information and policy. allows subnet to advertise its existence to rest of Internet: I am here! Computer Networks Network Layer 105 BGP Assumes an Arbitrary Interconnection of ASs Figure 4.4 A simple multi-provider Internet Computer Networks Network Layer 106 BGP Issues/Concerns Scalability: An Internet backbone router must be able to forward any packet destined anywhere in the Internet.

Having a routing table that will provide a match for any valid IP address. Autonomous nature of the domains It is impossible to calculate meaningful path costs for a path that crosses multiple Ass. A cost of 1000 across one provider might imply a great path but it might mean an unacceptable bad one from another provider. Issues of trust Provider A might be unwilling to believe certain advertisements from provider B. Computer Networks Network Layer 107 BGP-4: Border Gateway Protocol Define local traffic as traffic that originates at or terminates on nodes within an AS, and transit traffic as traffic that passes through an AS. Classify AS's into three types:

Stub AS:: an AS that has only a single connection to one other AS; such an AS will only carry local traffic (small corporation in Figure 4.4 ). Multihomed AS:: an AS that has connections to more than one other AS, but refuses to carry transit traffic (large corporation at the top in Figure 4.4). Transit AS:: an AS that has connections to more than one other AS, and is designed to carry both transit and local traffic (backbone providers in Figure 4.4). Computer Networks Network Layer 108 BGP BGP does not belong to either of the two main classes of routing protocols (distance vectors and link-state protocols). BGP advertises complete paths as an enumerated lists of ASs to reach a particular network. Hence, often referred to as a path-vector protocol. BGP paths need to be loop-free!! Carried AS numbers need to be unique. Computer Networks Network Layer 109

BGP Interdomain Routing Figure 4.5 Example of a network running BGP Computer Networks Network Layer 110 Loops in AS Topology Figure 4.6 Example of loop among autonomous systems Computer Networks Network Layer 111 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet

Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the

Internet RIP OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 112 Address Resolution Protocol (ARP) A mechanism is needed to translate IP addresses into DL layer addresses that make sense on that network (e.g., 48-bit Ethernet addresses on an Ethernet LAN). Address pair == (hostID, Network Point of Attachment address) where hostID == IP address NPA address == Ethernet address This translation is needed by a local interior router (e.g., R1 in Figure 3.14) and by hosts on

the LAN (e.g., H1- H3 in Figure 3.14) Computer Networks Network Layer 113 Routing in an internet Figure 3.14 A Simple internetwork with Three Routers Computer Networks Network Layer 114 Address Resolution Protocol (ARP) One solution :: have the router maintain a table of address pairs for all hosts attached to the LAN. Table is then copied to each host on the LAN. This will generate lots of extra traffic on the LAN. * a better solution:: each host dynamically learns the contents of this address pairs table using the LAN. This is the function performed by ARP (Address Resolution Protocol). Computer Networks Network Layer 115

Address Resolution Protocol (ARP) Each node maintains an address pairs table in its cache. If IP address of destination host is NOT found in the cache, it invokes ARP over the LAN. An ARP query for desired IP address is broadcast on the LAN. The query includes address pair of sending host. Each IP host receives the query and checks to see if it matches its own IP address. Computer Networks Network Layer 116 Address Translation Protocol (ARP) The target host sends an ARP reply with its DL layer address and adds sending address pair to its local table.

Query originator updates information in its cached ARP table. Note - target hosts will refresh their cache entry if originator is in local cache, but will not make a new table entry otherwise. ARP cache entries time out periodically (e.g., every 15 minutes) and non-refreshed entries are Computer Networks Network Layer 117 ARP Packet Format HardwareType: type of physical network (e.g., Ethernet) ProtocolType: type of higher layer protocol (e.g., IP) Hlen & Plen: length of link layer and protocol layer addresses Operation: request or response Figure 3.23 ARP packet format for mapping IP addresses into Ethernet addresses Computer Networks Network Layer

118 IP Addresses: How to Get One? Q: How does a host get IP address? hard-coded by system admin in a file Windows: control-panel->network>configuration->tcp/ip->properties UNIX: /etc/rc.config DHCP: Dynamic Host Configuration Protocol: A host dynamically gets address from a server. A plug-and-play protocol Computer Networks Network Layer 119 Host Configurations

Ethernet addresses are configured into network by manufacturer and they are unique. IP addresses must be unique on a given internetwork but also must reflect the structure of the internetwork. Most host Operating Systems provide a mechanism to manually configure the hosts IP information. Manual configuration disadvantages: A lot of work to configure all the hosts in a large network. Configuration process is error-prune. Automated Computer Configuration Process is required.120 Networks Network Layer DHCP Relies on the existence of a DHCP Server that provides configuration information. Uses UDP and ports 67 and 68. Has widespread use in wireless

LANs. DHCP server maintains a pool of available addresses that are allocated on demand. Computer Networks Network Layer 121 DHCP: Dynamic Host Configuration Protocol Goal: Allow a host to dynamically obtain its IP address from network server when it joins the network. Can renew its lease on address in use. Allows reuse of addresses (only hold address while connected an on). Support for mobile users who want to join network (more shortly). DHCP overview: 1. host broadcasts DHCP discover msg [optional] 2. DHCP server responds with DHCP offer msg [optional] 3. host requests IP address: DHCP request msg 4. DHCP server sends address: DHCP ack msg Computer Networks Network Layer 122 DHCP Client-Server Scenario A

223.1.1.1 DHCP server 223.1.1.2 223.1.1.4 223.1.2.9 B 223.1.1.3 223.1.3.1 223.1.2.1 223.1.3.27 223.1.2.2 223.1.3.2 E arriving DHCP client needs address in this network K&R Computer Networks Network Layer 123

DHCP Client-Server Scenario DHCP server: 223.1.2.5 1. DHCP discover src : 0.0.0.0, 68 dest.: 255.255.255.255,67 yiaddr: 0.0.0.0 transaction ID: 654 arriving client 2. DHCP offer src: 223.1.2.5, 67 dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4 transaction ID: 654 Lifetime: 3600 secs 3. DHCP request time src: 0.0.0.0, 68 dest:: 255.255.255.255, 67 yiaddrr: 223.1.2.4 transaction ID: 655 Lifetime: 3600 secs 4. DHCP ACK src: 223.1.2.5, 67 dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4

transaction ID: 655 Lifetime: 3600 secs Computer Networks Network Layer K&R 124 DHCP: More than IP address 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). Computer Networks Network Layer 125 DHCP Relay Agent Figure 3.24 DHCP relay agent receives DISCOVER message To avoid a DHCP server on every network, DHCP relay agent unicasts the message to DHCP server and waits for Computer the response. Networks Network Layer

126 DHCP: Example DHCP UDP IP Eth Phy DHCP DHCP DHCP DHCP DHCP DHCP DHCP DHCP DHCP connecting laptop needs its IP address, addr of first-hop router, addr of DNS server: use DHCP DHCP request DHCP

UDP IP Eth Phy 168.1.1.1 router (runs DHCP) encapsulated in UDP, encapsulated in IP, encapsulated in 802.1 EthernetEthernet. frame broadcast (dest: FFFFFFFFFFFF) on LAN, received at router running DHCP server. Ethernet demuxed to IP demuxed, UDP demuxed to DHCP. K&R Computer Networks Network Layer 127 DHCP: Example DHCP UDP IP

Eth Phy DHCP DHCP DHCP DHCP DHCP DHCP DHCP DHCP DHCP K&R DHCP UDP IP Eth Phy DCP server formulates DHCP ACK containing clients IP address, IP address of first-hop router for client, name & IP address of DNS server

encapsulation of router (runs DHCP) DHCP server, frame forwarded to client, demuxing up to DHCP at client. client now knows its IP address, name and IP address of DSN server, IP address of its first-hop router. Computer Networks Network Layer 128 DHCP: Wireshark Output (home reply LAN) Message type: Boot Request (1) Hardware type: Ethernet Hardware address length: 6 Hops: 0 Transaction ID: 0x6b3a11b7 Seconds elapsed: 0 Bootp flags: 0x0000 (Unicast) Client IP address: 0.0.0.0 (0.0.0.0) Your (client) IP address: 0.0.0.0 (0.0.0.0) Next server IP address: 0.0.0.0 (0.0.0.0) Relay agent IP address: 0.0.0.0 (0.0.0.0)

Client MAC address: Wistron_23:68:8a (00:16:d3:23:68:8a) Server host name not given Boot file name not given Magic cookie: (OK) Option: (t=53,l=1) DHCP Message Type = DHCP Request Option: (61) Client identifier Length: 7; Value: 010016D323688A; Hardware type: Ethernet Client MAC address: Wistron_23:68:8a (00:16:d3:23:68:8a) Option: (t=50,l=4) Requested IP Address = 192.168.1.101 Option: (t=12,l=5) Host Name = "nomad" Option: (55) Parameter Request List Length: 11; Value: 010F03062C2E2F1F21F92B 1 = Subnet Mask; 15 = Domain Name 3 = Router; 6 = Domain Name Server 44 = NetBIOS over TCP/IP Name Server request reply Message type: Boot Reply (2) Hardware type: Ethernet Hardware address length: 6 Hops: 0 Transaction ID: 0x6b3a11b7 Seconds elapsed: 0 Bootp flags: 0x0000 (Unicast) Client IP address: 192.168.1.101 (192.168.1.101) Your (client) IP address: 0.0.0.0 (0.0.0.0) Next server IP address: 192.168.1.1 (192.168.1.1)

Relay agent IP address: 0.0.0.0 (0.0.0.0) Client MAC address: Wistron_23:68:8a (00:16:d3:23:68:8a) Server host name not given Boot file name not given Magic cookie: (OK) Option: (t=53,l=1) DHCP Message Type = DHCP ACK Option: (t=54,l=4) Server Identifier = 192.168.1.1 Option: (t=1,l=4) Subnet Mask = 255.255.255.0 Option: (t=3,l=4) Router = 192.168.1.1 Option: (6) Domain Name Server Length: 12; Value: 445747E2445749F244574092; IP Address: 68.87.71.226; IP Address: 68.87.73.242; IP Address: 68.87.64.146 Option: (t=15,l=20) Domain Name = "hsd1.ma.comcast.net." Computer Networks Network Layer K&R 129 Network Layer Topics 4.1 Introduction 4.2 Virtual circuit and datagram

networks 4.3 Whats inside a router 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP

OSPF BGP 4.7 ICMP Computer Networks Network Layer K&R 130 NAT: Network Address Translation rest of Internet local network (e.g., home network) 10.0.0/24 10.0.0.4 10.0.0.1 10.0.0.2 138.76.29.7 10.0.0.3 Datagrams with source or All datagrams leaving local network have same single source destination in this network

have 10.0.0/24 address for NAT IP address: 138.76.29.7, different source port numbers source, destination (as usual). K&R Computer Networks Network Layer 131 NAT: Network Address Translation Motivation: local network uses just one IP address as far as outside world is concerned: range of addresses not needed from ISP: just one IP address for all devices. can change addresses of devices in local network without notifying outside world. can change ISP without changing addresses of devices in local network. devices inside local net not explicitly addressable, visible by outside world (a security plus). Computer Networks Network Layer 132 NAT: Network Address Translation

Implementation: NAT router must: 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 dest fields of every incoming datagram with corresponding (source IP address, port #) stored in NAT table. Computer Networks Network Layer 133 NAT: Network Address Translation NAT translation table WAN side addr LAN side addr 1: host 10.0.0.1 2: NAT router sends datagram to changes datagram 138.76.29.7, 5001 10.0.0.1, 3345 128.119.40.186, 80 source addr from 10.0.0.1, 3345

to 138.76.29.7, 5001, S: 10.0.0.1, 3345 D: 128.119.40.186, updates table 10.0.0.1 80 2 S: 138.76.29.7, 5001 D: 128.119.40.186, 80 138.76.29.7 S: 128.119.40.186, 80 D: 138.76.29.7, Reply arrives 5001 K&R 3 3: dest. address: 138.76.29.7, 5001

1 10.0.0.4 S: 128.119.40.186, 80 D: 10.0.0.1, 3345 10.0.0.2 4 10.0.0.3 4: NAT router changes datagram dest addr from 138.76.29.7, 5001 to 10.0.0.1, 3345 Computer Networks Network Layer 134 NAT Traversal Problem client wants to connect to server with address 10.0.0.1 server address 10.0.0.1 local to LAN (client cant use it as destination addr) only one externally visible NATted address: 138.76.29.7

Solution 1: statically configure NAT to forward incoming connection requests at given port to server Client 10.0.0.1 ? 10.0.0.4 138.76.29.7 NAT router e.g., (138.76.29.7, port 2500) always forwarded to 10.0.0.1 port 25000 Computer Networks Network Layer K&R 135 NAT Traversal Problem

Solution 2: Universal Plug and Play (UPnP) Internet 10.0.0.1 Gateway Device (IGD) IGD Protocol. Allows NATted 10.0.0.4 host to: learn public IP address 138.76.29.7 NAT (138.76.29.7) router add/remove port mappings (with lease times) i.e., automate static NAT port map configuration Computer Networks Network Layer K&R 136 NAT Traversal Problem Solution 3: relaying (used in Skype) NATed client establishes connection to relay External client connects to relay relay bridges packets between to connections 2. connection to

relay initiated by client Client 3. relaying established 1. connection to relay initiated by NATted host 138.76.29.7 10.0.0.1 NAT router K&R Computer Networks Network Layer 137 Network Layer Topics

4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol Datagram Format IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms

Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP ICMP Computer Networks Network Layer K&R 138 Internet Control Message Protocol (ICMP) IP is always configured with a companion protocol (ICMP) that defines a collection of error messages that are sent back to the source host whenever a router or host is unable to process an IP datagram successfully, e.g.,

Destination host unreachable due to link /node failure. Reassembly process failed. TTL had reached 0 (so datagrams don't cycle forever) IP header checksum failed ICMP includes several control messages that a router can use to send back to a source host. ICMP-Redirect Sent from router R1 to a source host to inform host there exists a better path through R2 to a particular destination. With a better route information Computer Networks Network Layer 139 Other ICMP functions ping uses ICMP echo messages to determine if a node is reachable and alive. Can be used to estimate RTT. traceroute is used to determine the set of routes along the path to a desintination. * Note - some routers send ICMP

packets through a separate special queue. Computer Networks Network Layer 140 Network Layer Summary 4.1 Introduction 4.2 Virtual circuit and datagram networks 4.3 What is inside a router? 4.4 IP: Internet Protocol Datagram Format

IPv4 addressing Subnets CIDR ARP & DHCP NAT 4.5 Routing algorithms Algorithm Classification Link State Distance Vector Hierarchical Routing 4.6 Routing in the Internet RIP OSPF BGP ICMP

Computer Networks Network Layer K&R 141

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