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IP Routing

IP Routing. MIS 4700 Dr. Garrett. 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

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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

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