1 Chapter 14-16a Internet Routing Review

Chapter 14-16: Internet Routing Review 2 Introduction Motivation: Router performance is critical to overall performance and QoS in the Internet and private internetworks. Consider: Motivation: Router performance is critical to overall performance and QoS in the Internet and private internetworks. Consider: –selecting best routes (optimize delay, load) –maintaining routing tables (router overhead) –router-generated management traffic Topics: Topics: –Overview of Graph Theory –Interior Routing Protocols –Exterior Routing Protocols

Chapter 14-16: Internet Routing Review 3 Graph Theory and Networks Network Nodes Network Links Size of G: |E| = 10 Order of G: |V| = 6

Chapter 14-16: Internet Routing Review 4 Graph Theory and Networks Weighted Digraph to Represent Link Costs

Chapter 14-16: Internet Routing Review 5 Spanning Trees

Chapter 14-16: Internet Routing Review 6 Link Cost Determination Shortest-path distance approach Shortest-path distance approach –hop count –each link has equal cost of one unit Shortest-path length approach Shortest-path length approach –each link has associated cost in each direction –weighted digraph

Chapter 14-16: Internet Routing Review 7 Breadth-First Search Produces a spanning tree rooted in V 1 Finds shortest-path distance from V 1 to all V

Chapter 14-16: Internet Routing Review 8 Dijkstra’s Link-State Algorithm Based on breadth-first search Running time order of |V| 2

Chapter 14-16: Internet Routing Review 9 Bellman-Ford Distance Vector Algorithm Running time order of |V| x |E|

Chapter 14-16: Internet Routing Review 10 Ex: Dijkstra vs. Bellman-Ford Least-cost routing algorithms

Chapter 14-16: Internet Routing Review 11 Interior/Exterior Routing Protocols Host h2 a b b a a C A B d c A.a A.c C.b B.a c b Host h1 Interior routing within network (AS) A Exterior routing routingbetweennetworks A and B Interior routing within network (AS) B

12 Chapter 15 Interior Routing Protocols

Chapter 14-16: Internet Routing Review 13 Internet Routing Example

Chapter 14-16: Internet Routing Review 14 Routing Table Fixed vs. Adaptive Routing?

Chapter 14-16: Internet Routing Review 15 Routing Information Protocol (RIP) Distance Vector Algorithm Distance Vector Algorithm –typically uses simple link delay count metric Small networks Small networks –fast and simple –max hop count = 15 (RIPv1) Adaptive Adaptive –updates sent approximately every 30 seconds –links are invalidated if no update in 180 seconds Uses UDP transport (port 520) Uses UDP transport (port 520)

Chapter 14-16: Internet Routing Review 16 RIP Messages Command –1 for request –2 for reply Version –1: RIPv1, RFC 1058 –2: RIP-2, RFC 1723 Address Family ID –always 2 for IP addresses IP address –non-zero network portion –zero host portion Cost Metric –typically 1 (i.e. hop count)

Chapter 14-16: Internet Routing Review 17 Open Shortest Path First Protocol (OSPF) Link-State Algorithm Link-State Algorithm –Dijkstra’s Algorithm –uses flooding to advertise, request info Preferred for TCP/IP-based internets Preferred for TCP/IP-based internets –scale, TOS, hierarchy of areas, etc. –multiple metrics… monetary cost, reliability, throughput, delay, arbitrary Adaptive Adaptive –routers flood with new data when a significant change occurs Sent as payload in IP datagram Sent as payload in IP datagram

Chapter 14-16: Internet Routing Review 18 Open Shortest Path First Protocol (Scale, Hierarchy)

Chapter 14-16: Internet Routing Review 19 OSPF Messages Version –2: current version Type –1: “Hello”, for discovery –2: database structure –3: request link-state –4: update link-state –5: acknowledge update Length of message Router ID –unique in a single area Area ID –unique to an AS Internet checksum Authentication Info –Type of authentication –64 bit authentication value OSPF Header

20 Chapter 16a Exterior Routing Protocols

Chapter 14-16: Internet Routing Review 21 Exterior Routing RIP OSPF BGP

Chapter 14-16: Internet Routing Review 22 Border Gateway Protocol (BGP-4) Path Vector Algorithm Path Vector Algorithm –cost metrics not used or advertised –each router specifies a complete path to all other nodes (e.g., from node A to node Z = ADFHKXZ) Facilitates routing based on policy instead of cost metrics Facilitates routing based on policy instead of cost metrics –use preferred routes, providers (based on policy) –avoid competitors, poor performers, etc. Adaptive Adaptive –peers exchange updates on demand –nodes may choose not to participate Uses TCP transport (port 179) Uses TCP transport (port 179)

Chapter 14-16: Internet Routing Review 23 Border Gateway Protocol Example A B C W X Y legend: customer network (Stub AS) provider network  W, X, Y, A, B and C are networks  Paths are specified as, for example:  Path (w, y) = wACy  Path (x, y) = xCy  BGP routers advertise (update) only those routes that are specified by administrative policy  would A advertise …ABx… or …ACx… ?

Chapter 14-16: Internet Routing Review 24 BGP Messages Common Attributes Marker –synchronization and authentication mechanism Length of message Type –open –open: establish a neighbor relationship –update –update: send/withdraw route information –keepalive –keepalive: acknowledge or confirm relationship –notification –notification: error detected

Chapter 14-16: Internet Routing Review 25 Inter-Domain Routing Protocol (IDRP) Exterior routing protocol for IPv6 Exterior routing protocol for IPv6 Uses path-vector routing algorithm Uses path-vector routing algorithm ISO standard, defined within OSI protocol family ISO standard, defined within OSI protocol family –but, not dependent on OSI model –can be used with any internet protocol stack (such as TCP/IP) –provides a superset of BGP-4 functions –can aggregate routing info… “confederations” Utilizes an underlying internet protocol (like IP) with its own handshaking mechanism to exchange routing messages Utilizes an underlying internet protocol (like IP) with its own handshaking mechanism to exchange routing messages