CS335 Networking & Network Administration

1. CS335 Networking &Network Administration Tuesday, May 18, 2010

2. Internet routing • Propagation of routing tables • Routing table updates

3. Static vs. dynamic routing • Static routes do not change • Routes are loaded when the system starts • Dynamic routes – table information changes over time • Routes are also loaded when the system starts • System also starts route propagation software or routing software • Routing software on one computer interacts with routing software on others to learn about optimal routes. Tables are then updated.

4. Static routing • Does not require extra routing software • Does not consume bandwidth • No CPU cycles used to propagate routing info

5. Default route

6. Static routes • Most hosts use static routing • Host’s routing table contains two entries • One for the network to which the host attaches • A default entry that directs all other traffic to a specific router

7. Dynamic routing • 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.

8. Routing in the global internet • To limit routing traffic, the Internet uses a two-level routing hierarchy. • Routers and networks are divided into groups • All routers in a group exchange routing information. • At least one router in each group summarizes information before passing it on to other groups

9. Autonomous system concept • The concept of groups of routers • Designers left the concept flexible to accommodate many possibilities of routing groups • Each group is an autonomous system • Each group shares routing information • The group’s information is summarized before being sent to other groups

10. Internet routing protocols • Interior gateway protocols (IGP’s) • Routers within an autonomous system use this to exchange routing information • Exterior gateway protocols (EGP’s) • A router from one system uses these protocols to exchange routing information with another autonomous system

11. Optimal routes • Optimal route is hard to define • Depends on the application • For an interactive login app a path with least delay is optimal • For a browser downloading a large graphic file a path with maximum throughput is optimal • For an audio webcast path with least jitter is best

12. Routing metrics • The measure of the path that routing software uses when choosing a route • Bandwidth – data capacity of a link • Delay – length of time required to move a packet along each link from source to destination • Load – amount of activity on a network resource such as a router or a link • Reliability – a reference to the error rate of each network link • Ticks – the delay on a data link using IBM PC clock ticks (approximately 55 milliseconds or 1/18 second) • Cost – an arbitrary value, usually based on bandwidth, monetary expense, or other measurement, that is assigned by a network administrator

13. Routing metrics • IGPs use routing metrics to find optimal routes • EGPs merely finds a path because it cannot compare routing metrics from multiple autonomous systems

14. Routes and data traffic • A response to a routing advertisement is data • Data traffic for a given destination flows in exactly the opposite direction of routing traffic

15. Border gateway protocol (BGP) • Routing among autonomous systems – BGP provides routing information at the autonomous system level • Provision for policies – BGP allows senders and receivers to enforce policies, a manager can restrict which routes BGP advertises to outsiders • 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 • Reliable transport – BGP uses TCP for all communication for the reliability of data transfer that TCP provides • ISPs use BGP to exchange routing information among autonomous systems in the global Internet

16. BGP resources • http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/bgp.htm • http://www.academ.com/nanog/feb1997/BGPTutorial/sld001.htm • http://www.bgp4.as/

17. RIP Routing information protocol • Routing within an autonomous system – RIP is designed as an IGP used to pass information among routers within an autonomous system • 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 • Unreliable transport – uses UDP • Broadcast of multicast delivery – intended for use over LANs that support broadcast

18. RIP Routing information protocol • 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 • Uses distance vector algorithm - http://www.freesoft.org/CIE/RFC/1058/6.htm • Passive version for hosts – although only a router can propagate routing information, RIP allows a host to listen passively and update its routing table

19. RIP • Chief advantage is simplicity • Needs little configuration • The routers broadcast messages to each other • After a short time all routers in an organization will have all routes to all destinations • Also handles propagation of the default route

20. RIP packet • A RIP update message

21. RIP • RIP is an Interior Gateway protocol (IGP) • Uses distance vector algorithm to propagate routing information • A router running RIP advertises the destinations it can reach along with a distance to each destination • Adjacent routers receive the information and update their routing tables

22. RIP Routing information protocol • http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/rip.htm • http://www.faqs.org/rfcs/rfc1058.html • http://www.networksorcery.com/enp/protocol/rip.htm

23. Open shortest path first protocol (OSPF) OSPF Graph

24. Open shortest path first protocol (OSPF) • Designed to scale better for large organizations • OSPF is an IGP to route within an autonomous system • Full CIDR support – includes the full 32 bit address mask with each address • Authenticated message exchange – OSPF can ensure that messages are only accepted from trusted sources • Imported routes – OSPF allows a router to introduce routes learned form other means (e.g., From BGP) • Uses link-state algorithm http://www.answers.com/topic/link-state-protocol • Has support for metrics

25. OSPF areas • Can scale to handle a larger number of routers than other IGPs • Does hierarchical routing • Allows a manger to divide the routers and networks in an autonomous system into subsets called areas • OSPF allows communication between areas • http://www.cisco.com/warp/public/104/1.html • http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ospf.htm

26. Multicast routing • IP multicast allows applications to: • Join multicast group at any time • Leave the group at any time • Membership in a multicast group is dynamic

27. IGMP Internet Group Multicast Protocol • The protocol uses a host to inform a router when it joins or leaves an Internet multicast group • IGMP is only used on the local network • Routers must use another multicast routing protocol to inform other routers of group membership

28. Forwarding and multicast techniques • Flood and prune • Configuration and tunneling • Core-based discovery

29. Multicast protocols • Distance vector multicast routing protocol (DVMRP) • Core based trees (CBT) • Protocol independent multicast – sparse mode (PIM-SM) • Protocol independent multicast – dense mode (PIM-DM) • Multicast extensions to the open shortest path first protocol (MOSPF) • The dynamics characteristics of Internet multicast make the problem of multicast route propagation difficult. Internet does not have an Internet-wide multicasting facility

30. Routing summary • Both hosts and routers contain an IP routing table. Hosts use a static table • Internet is divided into autonomous systems • EGPs and IGPs exchange routing information • Multicast route propagation is difficult • Many routing protocols