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IP Routing

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IP Routing

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  1. IP Routing MIS 4700 Dr. Garrett

  2. Understanding Routing • Routing table • Database that lives in the memory of the router • Entries in this database are known as “routes” • Network addresses • “next hop” • Metrics • Vendor-specific information • Compilation of information about all the networks that the router can reach

  3. Understanding Routing (cont.)

  4. Understanding Routing (cont.) • The routing table is used as follows: • Router reads destination address • Looks in the Network field of its routing table for a match • Finds a match, then it sends the packet to the corresponding next hop

  5. How Entries Are Placed in the Routing Table • Route entries can be placed in a routing table in three basic ways: • Direct connection • Manually configured • Exact configuration • Simple and secure • Dynamically with a routing protocol • Network Layer Reachability Information (NLRI)

  6. Routing Protocols and Routed Protocols • Routing protocols are used to exchange routing information • Routing Information Protocol (RIP) • Open Shortest Path First (OSPF) • Routed protocols are Layer 3 protocols that are used to get packets through an internetwork • Internet Protocol (IP) • Internetwork Packet Exchange (IPX)

  7. Grouping Routing Protocols • Two primary ways to group routing protocols • Routing domains or autonomous systems • Interior gateway protocols (IGPs) • Exterior gateway protocols (EGPs) • Functionality of routing protocols • Distance vector • Link-state

  8. Distance Vector Routing Protocols • Route by rumor • Periodically broadcast entire routing table • Considered “chatty” • Routing decisions are based on network distance • Routing Information Protocol (RIP) • Interior Gateway Routing Protocol (IGRP) • Border Gate Protocol (BGP)

  9. Distance Vector Routing Protocols (cont.)

  10. Routing Loops • One router believes the best path to a network is via a second router, and at the same time, the second router believes the best path to that network is through the first router • TTL

  11. Loop-Avoidance Schemes • Count to infinity • Network diameter • IP header TTL field • Split horizon • Poison reverse

  12. Link-State Routing Protocols • Generates information about directly connected neighbors • Flood network (update) with information • Update only when a link change is detected • All routers have identical view of network topology • Convergence time is short • Dijkstra algorithm • Build adjacencies with neighbor routers

  13. Link-State Routing Protocols (cont.)

  14. Routing Characteristics • Route convergence • Loop-free path to all networks • Split horizon • Poison reverse • Assigning costs to routes to prevent routing loops • Time to Live (TTL) • Defined in the Network layer header • Multicast vs broadcast update behavior

  15. Routing Characteristics (cont.) • ICMP router advertisements • Allow hosts to passively learn about available routes • Black holes • ICMP is turned off • Path Maximum • Transmission Unit black hole router • Areas, autonomous systems, and border routers

  16. Routing Characteristics (cont.)

  17. Routing Characteristics (cont.)

  18. Routing Characteristics (cont.)

  19. Routing Characteristics (cont.)

  20. Interior Gateway Protocols • RIP • RIPv1, RIPv2 • Distance vector routing protocol • UDP based • UDP port 520 • RIPv2 • Support for variable-length subnets

  21. RIPv1 • Broadcast routing table every 30 seconds • Does not support non-default subnet masks • A RIP packet can have up to 25 networks • RIPv1 packet format: • Command • Version • Reserved (or Zero) • Address Family Identifier • IP Address • Metric

  22. RIPv1 (cont.)

  23. RIPv1 (cont.)

  24. RIPv2 • Support of variable-length subnet masks • Basic authentication • Multicasts routing updates • RIPv2 packet format • Command • Version • Reserved • Address Family • Authentication Type

  25. RIPv2 (cont.) • RIPv2 packet format (cont.) • Authentication • Plain text passwords • Address Family Identifier • Route Tag • Internal route entry, external route entry • IP Address • Subnet Mask • Next Hop • Metric

  26. RIPv2 (cont.)

  27. Open Shortest Path First • Link-state routing protocol • Non-proprietary • Configurable metrics • Multicast Hello packets • Establish adjacencies

  28. Open Shortest Path First (cont.) • Dijkstra algorithm • Designated router (DR) • Backup designated router (BDR) • Link State Advertisements (LSA) • LSA multicast to DR (224.0.0.6)

  29. Open Shortest Path First (cont.)

  30. Open Shortest Path First (cont.) • Six types of LSAs • Type 1 (Router Links Advertisement) • Type 2 (Network Links Advertisement) • Type 3 (Network Summary Link Advertisement) • Type 4 (AS Boundary Router Summary Link Advertisement) • Type 5 (AS External Link Advertisement) • Type 7 (Not So Stubby Area Networks Advertisement)

  31. Open Shortest Path First (cont.)

  32. Open Shortest Path First (cont.) • OSPF header fields • Version Number Field • Type Field • Packet Length Field • Router ID Field • Area ID Field • Checksum Field • AuType Field • Authentication

  33. Open Shortest Path First (cont.)

  34. Enhanced Interior Gateway Routing Protocol (EIGRP) • Developed by Cisco in 1980s (IGRP) • Updated to EIGRP in early 1990s • Hybrid routing protocol • Integrates distance vector and link-state functions

  35. Enhanced Interior Gateway Routing Protocol (EIGRP) (cont.)

  36. Border Gateway Protocol • Exchange routing information between separate autonomous systems • Current version 4 • BGP offers three types of routing operations • Inter-autonomous system routing • Intra-autonomous system routing • Pass-through autonomous system routing

  37. Border Gateway Protocol

  38. Managing Routing On A In-House Internetwork • Routing protocols • Do not discriminate between users or types of traffic • Load balancing • Control network paths with Policy-based routing based on • Type of protocol, source/destination address

  39. Hybrid Networks • Supporting multiple routing protocol • Redistribution • Requires careful attention to configuration

  40. Routing On And Off A Wide Area Network • Several small offices • Hub and spoke • Multiprotocol • Mobile Users • Mobil IP • Local Area Mobility (LAM)

  41. Routing To And From The Internet • BGPv4 • Requires a major hardware investment • Only networks that connect to multiple ISPs should use BGP

  42. Securing Routers And Routing Behavior • Turn off unnecessary services, shut down unnecessary listening ports • Configure strong access security to prevent tampering, and, of course, secure physical access to the boxes • Assign secure encrypted passwords • Telnet sends unencrypted login names and passwords • Use secure routing protocols

  43. Troubleshooting IP Routing • Test connectivity with the following tools • ROUTE: Used to view the host’s local routing table, and add and remove route entries • PING • TRACERT • PATHPING