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May 16

  1. 1. CS335 Networking & Network Administration Tuesday, November 18, 2008
  2. 2. Internet routing <ul><li>Propagation of routing tables </li></ul><ul><li>Routing table updates </li></ul>
  3. 3. Static vs. dynamic routing <ul><li>Static routes do not change </li></ul><ul><ul><li>Routes are loaded when the system starts </li></ul></ul><ul><li>Dynamic routes – table information changes over time </li></ul><ul><ul><li>Routes are also loaded when the system starts </li></ul></ul><ul><ul><li>System also starts route propagation software or routing software </li></ul></ul><ul><ul><li>Routing software on one computer interacts with routing software on others to learn about optimal routes. Tables are then updated. </li></ul></ul>
  4. 4. Static routing <ul><li>Does not require extra routing software </li></ul><ul><li>Does not consume bandwidth </li></ul><ul><li>No CPU cycles used to propagate routing info </li></ul>
  5. 5. Default route
  6. 6. Static routes <ul><li>Most hosts use static routing </li></ul><ul><li>Host’s routing table contains two entries </li></ul><ul><li>One for the network to which the host attaches </li></ul><ul><li>A default entry that directs all other traffic to a specific router </li></ul>
  7. 7. Dynamic routing <ul><li>Each router runs routing software that learns about destinations other routers can reach and informs other routers about destinations that it can reach. Routing tables are updated continuously. </li></ul>
  8. 8. Routing in the global internet <ul><li>To limit routing traffic, the Internet uses a two-level routing hierarchy. </li></ul><ul><li>Routers and networks are divided into groups </li></ul><ul><li>All routers in a group exchange routing information. </li></ul><ul><li>At least one router in each group summarizes information before passing it on to other groups </li></ul>
  9. 9. Autonomous system concept <ul><li>The concept of groups of routers </li></ul><ul><li>Designers left the concept flexible to accommodate many possibilities of routing groups </li></ul><ul><li>Each group is an autonomous system </li></ul><ul><li>Each group shares routing information </li></ul><ul><li>The group’s information is summarized before being sent to other groups </li></ul>
  10. 10. Internet routing protocols <ul><li>Interior gateway protocols ( IGP’s ) </li></ul><ul><ul><li>Routers within an autonomous system use this to exchange routing information </li></ul></ul><ul><li>Exterior gateway protocols ( EGP’s ) </li></ul><ul><ul><li>A router from one system uses these protocols to exchange routing information with another autonomous system </li></ul></ul>
  11. 11. Optimal routes <ul><li>Optimal route is hard to define </li></ul><ul><li>Depends on the application </li></ul><ul><li>For an interactive login app a path with least delay is optimal </li></ul><ul><li>For a browser downloading a large graphic file a path with maximum throughput is optimal </li></ul><ul><li>For an audio webcast path with least jitter is best </li></ul>
  12. 12. Routing metrics <ul><li>The measure of the path that routing software uses when choosing a route </li></ul><ul><ul><li>Bandwidth – data capacity of a link </li></ul></ul><ul><ul><li>Delay – length of time required to move a packet along each link from source to destination </li></ul></ul><ul><ul><li>Load – amount of activity on a network resource such as a router or a link </li></ul></ul><ul><ul><li>Reliability – a reference to the error rate of each network link </li></ul></ul><ul><ul><li>Ticks – the delay on a data link using IBM PC clock ticks (approximately 55 milliseconds or 1/18 second) </li></ul></ul><ul><ul><li>Cost – an arbitrary value, usually based on bandwidth, monetary expense, or other measurement, that is assigned by a network administrator </li></ul></ul>
  13. 13. Routing metrics <ul><li>IGPs use routing metrics to find optimal routes </li></ul><ul><li>EGPs merely finds a path because it cannot compare routing metrics from multiple autonomous systems </li></ul>
  14. 14. Routes and data traffic <ul><li>A response to a routing advertisement is data </li></ul><ul><li>Data traffic for a given destination flows in exactly the opposite direction of routing traffic </li></ul>
  15. 15. Border gateway protocol (BGP) <ul><li>Routing among autonomous systems – BGP provides routing information at the autonomous system level </li></ul><ul><li>Provision for policies – BGP allows senders and receivers to enforce policies, a manager can restrict which routes BGP advertises to outsiders </li></ul><ul><li>Facilities for transit routing – BGP classifies each autonomous system as a transit system if it agrees to pass traffic to another autonomous system or as a stub system if it does not </li></ul><ul><li>Reliable transport – BGP uses TCP for all communication for the reliability of data transfer that TCP provides </li></ul><ul><li>ISPs use BGP to exchange routing information among autonomous systems in the global Internet </li></ul>
  16. 16. BGP resources <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  17. 17. RIP Routing information protocol <ul><li>Routing within an autonomous system – RIP is designed as an IGP used to pass information among routers within an autonomous system </li></ul><ul><li>Hop count metric – RIP measures distance in network hops where each network between source and destination is a single hop. Origin-one counting where a directly connected network is 1 hop away, not zero </li></ul><ul><li>Unreliable transport – uses UDP </li></ul><ul><li>Broadcast of multicast delivery – intended for use over LANs that support broadcast </li></ul>
  18. 18. RIP Routing information protocol <ul><li>Support for default route propagation – allows a router to advertise a default route. An organization can use RIP to install a default route in each router such that the default routes all forward traffic to the ISP </li></ul><ul><li>Uses distance vector algorithm - </li></ul><ul><li>Passive version for hosts – although only a router can propagate routing information, RIP allows a host to listen passively and update its routing table </li></ul>
  19. 19. RIP <ul><li>Chief advantage is simplicity </li></ul><ul><li>Needs little configuration </li></ul><ul><li>The routers broadcast messages to each other </li></ul><ul><li>After a short time all routers in an organization will have all routes to all destinations </li></ul><ul><li>Also handles propagation of the default route </li></ul>
  20. 20. RIP packet <ul><li>A RIP update message </li></ul>
  21. 21. RIP <ul><li>RIP is an Interior Gateway protocol (IGP) </li></ul><ul><li>Uses distance vector algorithm to propagate routing information </li></ul><ul><li>A router running RIP advertises the destinations it can reach along with a distance to each destination </li></ul><ul><li>Adjacent routers receive the information and update their routing tables </li></ul>
  22. 22. RIP Routing information protocol <ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  23. 23. Open shortest path first protocol (OSPF) <ul><li>OSPF Graph </li></ul>
  24. 24. Open shortest path first protocol (OSPF) <ul><li>Designed to scale better for large organizations </li></ul><ul><li>OSPF is an IGP to route within an autonomous system </li></ul><ul><li>Full CIDR support – includes the full 32 bit address mask with each address </li></ul><ul><li>Authenticated message exchange – OSPF can ensure that messages are only accepted from trusted sources </li></ul><ul><li>Imported routes – OSPF allows a router to introduce routes learned form other means (e.g., From BGP) </li></ul><ul><li>Uses link-state algorithm </li></ul><ul><li>Has support for metrics </li></ul>
  25. 25. OSPF areas <ul><li>Can scale to handle a larger number of routers than other IGPs </li></ul><ul><li>Does hierarchical routing </li></ul><ul><li>Allows a manger to divide the routers and networks in an autonomous system into subsets called areas </li></ul><ul><li>OSPF allows communication between areas </li></ul><ul><li> </li></ul><ul><li> </li></ul>
  26. 26. Multicast routing <ul><li>IP multicast allows applications to: </li></ul><ul><ul><li>Join multicast group at any time </li></ul></ul><ul><ul><li>Leave the group at any time </li></ul></ul><ul><ul><li>Membership in a multicast group is dynamic </li></ul></ul>
  27. 27. IGMP Internet Group Multicast Protocol <ul><li>The protocol uses a host to inform a router when it joins or leaves an Internet multicast group </li></ul><ul><li>IGMP is only used on the local network </li></ul><ul><li>Routers must use another multicast routing protocol to inform other routers of group membership </li></ul>
  28. 28. Forwarding and multicast techniques <ul><li>Flood and prune </li></ul><ul><li>Configuration and tunneling </li></ul><ul><li>Core-based discovery </li></ul>
  29. 29. Multicast protocols <ul><li>Distance vector multicast routing protocol ( DVMRP ) </li></ul><ul><li>Core based trees (CBT) </li></ul><ul><li>Protocol independent multicast – sparse mode ( PIM-SM ) </li></ul><ul><li>Protocol independent multicast – dense mode ( PIM-DM ) </li></ul><ul><li>Multicast extensions to the open shortest path first protocol ( MOSPF ) </li></ul><ul><li>The dynamics characteristics of Internet multicast make the problem of multicast route propagation difficult. Internet does not have an Internet-wide multicasting facility </li></ul>
  30. 30. Routing summary <ul><li>Both hosts and routers contain an IP routing table. Hosts use a static table </li></ul><ul><li>Internet is divided into autonomous systems </li></ul><ul><li>EGPs and IGPs exchange routing information </li></ul><ul><li>Multicast route propagation is difficult </li></ul><ul><li>Many routing protocols </li></ul>