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Module 5 : Route Optimization

Module 5 : Route Optimization. By Sang Gon Lee Spring 2008. Contents. Routing updates compete with user data for bandwidth and router resources.

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Module 5 : Route Optimization

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  1. Module 5 : Route Optimization By Sang Gon Lee Spring 2008

  2. Contents • Routing updates compete with user data for bandwidth and router resources. • In some cases, the updates may not be required and yet are still advertised by default, contributing to bandwidth waste and increasing security risks. • This module examines the key IOS route optimization features, including route redistribution, routing update control, and policy-based routing. In addition, an overview of DHCP and how to configure support for it is covered.

  3. 5.1 Operating a Network Using Multiple Routing Protocols

  4. Using Multiple Routing Protocols • multiprotocol routing: • company mergers, • multiple departments managed by multiple network administrators, • multivendor environments, or simply because the original routing protocol is no longer the best choice. • Route redistribution • using a routing protocol to advertise routes that are learned by some other means, such as by another routing protocol, static routes, or directly connected routes

  5. Defining Route Redistribution • Redistribution : how routers connect different routing domains so that they can exchange and advertise routing information between the different autonomous systems.

  6. Redistributing Route Information • Factors that have the most impact on redistribution include: • Metrics • Administrative distance • Classful/classless capabilities of the protocols

  7. Using Seed Metrics • the initial seed metric : should be set to a value larger than the largest metric within the receiving autonomous system to help prevent suboptimal routing and routing loops

  8. Seed Metrics Example +

  9. Defining Administrative Distance

  10. Defining Administrative Distance • OSPF route is preferred.

  11. Defining Administrative Distance • Prefix Lengths = subnet mask length • Varying prefix lengths of routes from different routing protocols affects routing decisions. • Longer prefixes are always preferred over shorter ones when forwarding a packet, regardless of routing protocols. • A packet destined for 192.168.32.1 VIA which NW? 10.1.1.1 • A packet destined for 192.168.32.100  VIA which NW? 10.1.1.2 • 192.168.32.100 does not fall within 192.168.32.0/26 (192.168.32.0 through 192.168.32.63), • it falls within the 192.168.32.0/24 destination (192.168.32.0 through 192.168.32.255).

  12. Modifying Administrative Distances

  13. Modifying Administrative Distances

  14. 5.2 Configuring and Verifying Router Redistribution

  15. Configuring Redistribution • Consider these points: • Only protocols that support the same protocol stack are redistributed. For example, between IP RIP and OSPF (O), because they both support the TCP/IP stack. between IPX RIP and OSPF (X), because IPX RIP supports the IPX/SPX stack and OSPF does not. • The method used to configure redistribution varies slightly among different routing protocols and combinations of routing protocols. some routing protocols require a metric to be configured during redistribution, but others do not.

  16. Configuring Redistribution • Generic steps apply to all routing protocol redistribution • Locate the boundary router that requires configuration of redistribution. • Determine which routing protocol is the core or backbone protocol. • Determine which routing protocol is the edge or short-term (in the case of migration) protocol. Determine whether all routes from the edge protocol need to be propagated into the core. Consider methods that reduce the number of routes. • Select a method for injecting the required edge protocol routes into the core. Simple redistribution using summaries at network boundaries minimizes the number of new entries in the routing table of the core routers.

  17. Redistributing Routes into a Classful Routing Protocol

  18. Redistributing Routes into a Classful Routing Protocol

  19. Redistributing from Classless to Classful Protocols • A common problem with redistributing routes between RIP and OSPF • RIP does not advertise routes out an interfaceif those routes are on the same major network but have a different mask than that particular interface. • OSPF Has a Longer Mask Than RIP • RIP과 OSPF는 동일 major 네트워크 상에. • OSPF 쪽의 SM가 길다. • Redistribution 안된다. • 해결책 : 1) 사자(使者)를 적진에 파견 2) 사자가 트래픽을 RTB가지 유인3) RTB는 OSPF 영역의 구체적인 경로 정보를 보유하고 있다. ip route 128.103.35.0 255.255.255.0 null0router rip redistribute static default metric 1

  20. Redistributing from Classless to Classful Protocols • RIP’s SM : 255.255.255.248 • OSPF’s SM : 255.255.255.240 • Redistribution 안된다. • OSPF의 큰 네트워크를 작은 네트워크 단위로 분할하여Static 선언  redistribute • On RTB • RIP Has a Longer Mask Than OSPF

  21. Redistributing Routes into a Classless Routing Protocol

  22. Redistributing Routes into a Classless Routing Protocol

  23. Redistributing Routes into OSPF Example

  24. Redistributing Routes into EIGRP

  25. Redistributing Routes into EIGRP

  26. Redistributing Routes into EIGRP Example

  27. Redistributing Static and Connected Routes

  28. Verifying Route Redistribution

  29. Verifying Route Redistribution Example

  30. Administrative Distance Problems with Redistribution • 무엇이 문제? • 경계 라우트(프로토콜 사이의 경계)가 둘 이상 있는 경우,(예) OSPF와 RIP의 경계에서 (1) 10.3.3.0 네트워크를 P3R2는 RIP을 통해 알고 P3R1을 통해OSPF로 재 분재된 경로를 알게된다. (2) P3R2는 OSPF를 통해 배운 우회경로(준최적)가 라우팅 테이블에 들어간다. ( AD 문제) (3) P3R1에서도 동일한 현상이 일어난다.

  31. Administrative Distance Solution with Redistribution • 해결책 : – 재 분배되는 경로의 AD 값을 해당 영역 라우팅 프로토콜의 AD 보다 더 큰 값으로 설정하여 주입.  우회경로가 선정되는 경우 방지.

  32. 5.3 Controlling Routing Update Traffic

  33. Controlling Routing Updates • Passive interfaces • Distribution lists • Policy routing using route maps

  34. Passive Interfaces

  35. Passive Interface Considerations • 라우터에 많은 인터페이스가 있을 경우, 각각 인터페이스를 수동으로 일일이 passive 선언하는 것은 성가신 일. • 일괄적으로 전체를 passive 선언하고 필요한 부분만 푼다.

  36. Configuring Route Filtering Using Distribute Lists • Some ways to control or prevent dynamic routing updates are as follows: • Passive interface • Default routes. • Static routes • Distribution List • control routing updates is with a distribute list • Apply access control list (ACL) to routing updates • Incoming interface • Outgoing interface • Redistribution from another routing protocol

  37. Implementing the Distribute List

  38. Implementing the Distribute List

  39. Filtering Routing Updates with a Distribute List

  40. Controlling Redistribution with Distribute Lists • Route feedback occurs when routes originally learned from one routing protocol are redistributed back into that protocol. 이중 경로가 있을 때 원하는 경로만 재분배 함으로써 route feedback을 막을 수 있다. • D에도 유사하게 설정

  41. ???

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