Route Optimization

1. Route Optimization Chapter 10

2. Route Filters • Use access list to filter out unwanted routes • Identifies packets or addresses to be filtered • Prevents certain routes from being advertised • Controls routing updates

3. Filtering • Access Groups • Distribute List • Route Maps

4. Access Lists • List of routes or packets to permit or deny • Order of statements in access list is important • If packet matches access list, router goes to next statement • If packet does not match access list, router denies or permits packet • If packet does not match anything on access list, implicit denial causes router to deny packet

5. Access Groups • Access Groups are applying the access lists you learned about in 240 Router(config)#access list 100 deny ip 192.168.24.0 0.0.0.255 192.168.50.0 0.0.0.255 Router(config)#access list 100 permit ip any any Router(config)#int f0/0 Router (config-if)#ip access-group 100 in

6. How Route Filters Work • Route filters use access lists to accept or reject routes • Filter both routes advertised and incoming routes accepted from other routers • Router examines interface to see if routing filter is applied • If so, examines access list to see if route should be dropped in update • If route matches statement in list, processes it according to deny or permit keyword • If route does not match statement, route is dropped by implicit denial

7. Configuring Route Filters • Steps to configure route filter include • Creating access list to match routes • Determine which interface(s) to apply route filter to and whether it will apply to incoming or outgoing route updates • Apply route filter with distribute-list command

8. Distribute List • Blocks the advertising of a route by using a Access List • Applied to the Router not the interface • Can block out a certain interface or all

9. Router(config)#access list 1 deny 192.168.50.0 0.0.0.255 Router(config)#access list 1 permit any Router(config)#access list 2 deny 192.168.88.0 0.0.0.255 Router(config)#access list 2 permit any Router(config)#router eigrp 100 Router(config-router)#distribute-list 1 out s1 Router(config-router)#distribute-list 2 out Router(config)#access list 100 permit ip any any

10. Using Route Maps to Implement Routing Policy • Configure policy-based routing • Routes packets differently based on properties of packets • Introduced in Cisco 11.0 • Use to mark packet with precedence or TOS value • Provides different Quality of Service (QOS) to different types of traffic • Can use values in queuing packets • Allows service providers to route packets from different sources through different paths

11. How Route Maps Work • Route maps make policies based on attributes of a packet: • Source address of packet • Protocol • Application • Packet size • Route map has series of permit and deny statements • Unlike access lists, route maps are processed in order specified by sequence number

12. Processing Route Maps • Each permit or deny statement works like if/then statement • If packet matches the match statement, router applies set command to packet • If packet doesn’t match any statement in route map, it is denied • May add statement at end to match all packets calling for some default action

13. Policy-Based Routing Router(config)#access-list 100 permit ip 192.168.200.0 0.0.0.255 192.168.50.0 0.0.0.255 Router(config)#access-list 100 permit ip 192.168.200.0 0.0.0.255 192.168.100.0 0.0.0.255 Router(config)#access-list 110 permit ip 192.168.50.0 0.0.0.255 Router(config)#access-list 110 permit ip 192.168.100.0 0.0.0.255 Router(config)#route-map POLICY1 permit 10 Router(config-route-map)#match ip address 100 Router(config-route-map)#set interface s0/0 Router(config-route-map)#route-map POLICY1 permit 20 Router(config-route-map)#match ip address 110 Router(config-route-map)#set interface s0/1 Router(config-route-map)#exit Router(config)#interface s1/1 Router(config-if)#ip policy route-map POLICY1 Router(config-if)#int f0/0 Router(config-if)#ip policy route-map POLICY1

14. Benefits and Disadvantages of Route Redistribution • Redistribute routes for a variety of reasons • When two organizations merge, to redistribute routes between Autonomous Systems • When migrating from one interior gateway protocol to another • When you must use multiple routing protocols on parts of network • To use different routing protocols on different sections of hierarchical network

15. Redistributing Routes • Allows one routing protocol to exchange information with different routing protocol • Border router takes routes learned from one source of routing information and injects them into second • Alternative to using work-intensive static routing

16. Two Connected Autonomous Systems

17. Potential Redistribution Problems • Several potential problems • Routing loops • Poor path selection • Inconsistent convergence times

18. Protocol Considerations • Routing protocols must support same routed protocol stack to redistribute • Protocol determines how you redistribute routes • Automatically redistributes between EIGRP and IGRP in same Autonomous System • EIGRP metrics equal IGRP metrics multiplied by 256 • Automatically redistributes between IPX and AppleTalk

19. Configuring Route Redistribution • Steps to configure basic route redistribution • Identify border routers that will redistribute routes • Decide which protocols will inject routes into other routing protocol • Enter routing configuration mode for protocol that will learn routes • Configure route distribution between two routing protocols • May need to redistribute one instance of routing protocol into another

20. Setting Default Metrics • Two ways to set a default or seed metric • Use the default-metric command with arguments • Bandwidth - minimum in Kbps • Delay - in tens of microseconds • Reliability - with number from 1-255 where 255 means 100% reliable • Loading - with number from 1-255 where 255 means 100% loaded • MTU - in bytes • Use metric-value keyword with redistribute command

21. RIP Redistribution Router(config)#router rip Router(config-router)#redistribute igrp 100 metric 1 Router(config)#router rip Router(config-router)#default-metric 1 Router(config-router)#redistribute igrp 100

22. IGRP Distribution Router(config)#router igrp 100 Router(config-router)#redistribute rip metric 100 100 200 1 1500 Router(config)#router igrp 100 Router(config-router)#default-metric 100 100 200 1 1500 Router(config-router)#redistribute rip

23. OSPF Distribution Router(config)# router ospf 1 Router(config-router)# redistribute eigrp 100 metric 100 subnets Allows Classless routers to be redistributed

24. Static, Default, and Connected Routes • Situations where static or default routes are better than dynamic routes • Stub networks with only one outgoing connection • Internet connections • Back-up links • Static routes must be redistributed for other routers in Autonomous System to use them

25. Redistributing Static Routes • To configure a static route, use ip route command • Route tag lets you match a static route in route maps • Permanent keyword makes router keep route in its routing table even if associated interface goes down • Static routes can be configured to go through an interface instead of next hop

26. Redistributing Connected Routes • Use redistribute connected command to redistribute any connected network • By default, all connected networks are redistributed • Can use route filter to remove network that should not be redistributed • Use redistribute static command to redistribute between routing protocols

27. Redistributed Static and Connected Routes

28. Redistributing Default Routes • Special type of static route • Two ways to configure default route: • Use ip route 0.0.0.0 0.0.0.0 next-hop command • Use ip default-network network command • Can help router choose default gateway or gateway of last resort • Protocol determines how commands are used • Weigh benefits of static and dynamic routes against disadvantages

29. Redistributing into Classful Routing Protocols • Potential problems when redistributing between classless routing protocols with VLSMs those that do not support VLSMs • Classless routing protocols may inject routes that are not subnetted along classful boundaries

30. Two Strategies to Solve Problem • Propagate default route to OSPF domain through RIPv1 domain • Summarize or filter routes injected from OSPF domain to make RIPv1 routers learn only about routes with classful netmasks

31. Clean Up Routing Tables Before Redistribution • Prevent potential problems by simplifying topology of each Autonomous System before redistribution • Reduce amount of routing information that each protocol redistributes • Reduce size of routing table • Use route filters and route maps

32. Changing Metrics with Route Maps • Identify routes whose metrics you want to change • Steps to change metrics • Write access list identifying routes to be matched • Define route map identifying routes with match statement • Use set command to set metric for routes • Decide how to handle all other routes • Use redistribution command to activate redistribution, set default metric, and activate the route map

33. One-Way Redistribution Through a Single Border Router • Two Autonomous Systems redistributing routes at a single router • Packets traveling from one AS to other go through border router • For RIP domain, redistribute default route and use ip classless command • For EIGRP domain, use static route to allow EIGRP AS to learn about routes in RIP AS • Disadvantage is single point of failure

34. Redistributing from RIP into EIGRP with a Default Route

35. One-Way Redistribution Through Multiple Border Routers • Connect two Autonomous Systems at multiple places to avoid single point of failure • Set seed metric for RIP router redistribution into EIGRP

36. Possible Problems with Multiple Border Routers • Possible problem since both EIGRP and RIP propagate default routes • All packets sent on Internet may enter routing loop if primary route to Internet is down • Solution is to filter default route so that EIGRP Autonomous System does not learn about it

37. EIGRP Autonomous System Connected to OSPF AS • Each Autonomous System has default route to the Internet • Neither Autonomous System can use a default route to get to each other • Each Autonomous System must learn routes from the other

38. Redistributing OSPF into EIGRP • Set seed metrics for routes redistributed into each routing protocol • Use match keyword to match only certain types of routes • Use subnets keyword to have protocol inject information about subnets

39. Redistributing EIGRP into OSPF • Redistribution does not allow control of types of routes injected into OSPF • Use a route filter to eliminate problems • Identify networks to be filtered and make an access list • Use distribute-list out command to apply access list

40. Monitoring and Troubleshooting Redistribution • Two ways to verify that route redistribution is configured • Use show running-config command • Use show ip protocols command • Use show ip route command to examine routing tables

41. Troubleshooting Redistribution Problems • Examine topology of each involved Autonomous System • Examine routing tables of any border routers • Examine routing tables of routers inside each Autonomous System • Use ping and traceroute commands to check routes crossing the boundary between Autonomous Systems • Use debug commands on routers that seem to have a problem