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Pass4sure 300-101 CCNP Routing And Switching Protocol

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Pass4sure 300-101 CCNP Routing And Switching Protocol

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  1. Switch and Routing Protocols CCNP Routing and Switching ROUTE 300-101 1

  2. Overview • • • • • • • • • • Explain the significance of static routing Configure static and default routes Verify and troubleshoot static and default routes Identify the classes of routing protocols Identify distance vector routing protocols Identify link-state routing protocols Describe the basic characteristics of common routing protocols Identify interior gateway protocols Identify exterior gateway protocols Enable Routing Information Protocol (RIP) on a router 2

  3. The Routing Table • Before we begin lets see lets discuss the routing table and directly connected routes. • This is information which is not in the curriculum, but will give you a better understanding of what is taking place. 3

  4. Directly Connected Networks and the IP Routing Table 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.0.0.0/8 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route, o - ODR Gateway of last resort is not set RTA# The Routing Table prior to any interface configuration • The command to view the IP Routing table is: (priviledge or user mode) Router# show ip route • Currently, no routes in the routing table. 4

  5. Directly Connected Networks and the IP Routing Table 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.0.0.0/8 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#inter e 0 RTA(config-if)#ip add 192.168.2.1 255.255.255.0 RTA(config-if)#no shutdown RTA#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> C 192.168.2.0/24 is directly connected, Ethernet0 RTA# • Adding an ip address/mask to an interface tells the router that it is a member, “Directly Connected” to that network – just like when a host computer is configured with an ip address/mask. Notice the route is shown with the subnet mask and the “exit-interface.” Don’t forget the “no shutdown” Don’t forget the interface must be in “up” and “up” • • • 5

  6. Directly Connected Networks and the IP Routing Table RTA# debug ip routing RTA(config)#inter e 0 RTA(config-if)#ip add 192.168.2.1 255.255.255.0 RTA(config-if)#no shutdown 00:28:56: RT: add 192.168.2.0/24 via 0.0.0.0, connected metric [0/0] 00:28:56: RT: interface Ethernet0 added to routing table RTA#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> C 192.168.2.0/24 is directly connected, Ethernet0 RTA# undebug all Viewing the Routing Table Process • Use the “debug ip routing” command to view the Cisco IOS routing table process of adding a directly connected network to the routing table. • When finished, be sure to use “undebug all” • Debug commands are used to view detailed information about Cisco IOS processes – more later. 6

  7. Directly Connected Networks and the IP Routing Table RTA# debug ip routing RTA(config)#inter e 0 RTA(config-if)#shutdown 00:34:38: RT: interface Ethernet0 removed from routing table 00:34:38: RT: del 192.168.2.0 via 0.0.0.0, connected metric [0/0] 00:34:38: RT: delete network route to 192.168.2.0 RTA#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> RTA# undebug all Viewing the Routing Table Process • Directly connected routes will also be removed if the link goes down. • Directly connected routes will only be in the routing table if, it is not administratively down, the line is “up” and protocol is “up” • For serial interfaces, don’t forget the “clock rate” command on the router with the DCE cable – neither interface will be “up” and “up” until both ends are configured correctly. 7

  8. Directly Connected Networks and the IP Routing Table 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.0.0.0/8 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> C 172.16.0.0/16 is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0 RTB#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> C 172.16.0.0/16 is directly connected, Serial0 C 192.168.1.0/24 is directly connected, Serial1 RTC#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> C 10.0.0.0/8 is directly connected, Ethernet0 C 192.168.1.0/24 is directly connected, Serial1 The Routing Tables • Notice that the routers only know about their own directly connected networks. • They are not sharing routing information because we have not configured any static routes or dynamic routing protocols. 8

  9. Directly Connected Networks and the IP Routing Table 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTC(config)#inter e 0 RTC(config-if)#ip add 10.1.0.1 255.255.0.0 RTC#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> 10.0.0.0/16 is subnetted, 1 subnets C 10.1.0.0 is directly connected, Ethernet0 C 192.168.1.0/24 is directly connected, Serial1 RTC# Configuring an interface which has a subnet mask greater than the classful mask • We will discuss this in much more detail later using the presentation – “The Routing Table.” • For now, notice that when the subnet mask is not a classful mask, but a subnetted /16 mask. • The routing table information shows the route to the subnetted network • The mask is shown in the above, “parent” classful network. 9

  10. Directly Connected Networks and the IP Routing Table 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA#show ip route C 172.16.0.0/16 is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0 RTA#ping 172.16.0.1 !!!!! RTA#ping 172.16.0.2 !!!!! RTA#ping 192.168.1.1 ..... RTA#ping 192.168.1.2 ..... RTA#ping 10.1.0.1 ..... Routing – Only directly connected hosts (routers) • Routers can only reach networks known about in its own routing table. 10

  11. Directly Connected Networks and the IP Routing Table 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA#show ip route C 172.16.0.0/16 is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0 RTA#ping 172.16.0.1 Sending 5, 100-byte ICMP Echos to 172.16.0.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 56/57/60 ms RTA#ping 172.16.0.2 !!!!! Routing– Routing tables must have the necessary network routes • Question: If RTA can ping RTB’s 172.16.0.2 interface why can’t it ping RTB’s 192.168.1.1 interface? - RTA does not have a route to it in its routing table. • Question: Would an extended ping from RTA, using the source IP address of 192.168.2.1 be able to ping 172.16.0.1 on RTB? Why or why not? Where does the echo request or echo reply fail? 11

  12. Directly Connected Networks and the IP Routing Table 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA#show ip route C 172.16.0.0/16 is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0 RTB#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> C 172.16.0.0/16 is directly connected, Serial0 C 192.168.1.0/24 is directly connected, Serial1 RTA#ping Protocol [ip]: Target IP address: 172.16.0.2 Extended commands [n]: y Source address or interface: 192.168.2.1 Sending 5, 100-byte ICMP Echos to 172.16.0.2, timeout is 2 seconds: ..... Routing– Routing tables must have the necessary network routes • Question: Would an extended ping from RTA, using the source IP address of 192.168.2.1 be able to ping 172.16.0.1 on RTB? Why or why not? • The echo request from RTA reaches RTB because RTA has a route to 172.16.0.0/16 in its routing table. • However, the echo reply from RTB back to RTA fails, because RTB does not have a route for 192.168.2.0/24 in its routing table. 12

  13. Directly Connected Networks and the IP Routing Table 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> C 172.16.0.0/16 is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0 RTB#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> C 172.16.0.0/16 is directly connected, Serial0 C 192.168.1.0/24 is directly connected, Serial1 RTC#show ip route Codes: C - connected,.. <Other codes and gateway information omitted> 10.0.0.0/16 is subnetted, 1 subnets C 10.1.0.0 is directly connected, Ethernet0 C 192.168.1.0/24 is directly connected, Serial1 Routing Table Principles Revisited (Zinin, Cisco IP Routing) • Every router makes its decision alone, based on the information it has in its own routing table. • The fact that one router has certain information in its routing table does not mean that other routers have the same information. • Routing information about a path from one network to another does not provide routing information about the reverse, or return path. 13

  14. Routing Types 14

  15. Static Route Operation Hoboken#show ip route Codes: C - connected, S - static, S 172.16.1.0/24 [1/0] is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0 15

  16. ip route command RTR(config)# ip route prefix mask {address | interface} [distance] [tag tag] [permanent] • prefix IP route prefix for the destination. • mask Prefix mask for the destination. • address IP address of the “next hop” that can be used to reach that network. • interface Network interface to use (exit-interface) • distance (Optional) An administrative distance. • tag tag (Optional) Tag value that can be used as a "match" value for controlling redistribution via route maps. (CCNP Advanced Routing) • Permanent (Optional) Specifies that the route will not be removed, even if the interface shuts down. (CCNP Advanced Routing) 16

  17. Static Route Operation • If the exit interface (gateway) is “down” the static route will not be put in the routing table. 17

  18. Static Route Operation • If the router cannot reach the outgoing interface that is being used in the route, the route will not be installed in the routing table. This means if that interface is down, the route will not be placed in the routing table. • 18

  19. Administrative Distance and Metric Hoboken#show ip route Codes: C - connected, S - static, S 172.16.1.0/24 [1/0] is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0 • [ administrative distance / routing metric (or cost) ] • The cost for all static routes is “0” • The default administrative distance for static routes is “1” 19

  20. Administrative Distance • • • Administrative Distance is the “trustworthiness” of the routing information. Lower the administrative distance the more trustworthy the information. If the router hears about a route to the same network from more than one source it will use the administrative distance to decide which route to put in the routing table. 20

  21. Examples from the curriculum 21

  22. Examples from the curriculum • Two choices. • We will see the differences in a moment. 22

  23. Examples from the curriculum • The network 0.0.0.0 and mask 0.0.0.0 are known as a “default route” • Can be written 0.0.0.0/0 • Known as a “quad zero” route” • More later 23

  24. Static Routing • Some extra information on static routing that is not in the curriculum 24

  25. Static Routing Router(config)#ip route destination-prefix destination- prefix-mask {address | interface} [distance] [tag tag] [permanent] 25

  26. Static Routing 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 Configuring static routes • Routers do not need to configure static routes for their own directly connected networks. • We need to configure static routes for networks this router needs to reach. • We will need to configure static routes for the other routers as well, as “routing information about a path from one network to another does not provide routing information about the reverse, or return path.” • Convergence – When all the routers in the network (AS) have accurate and consistent information, so that proper routing and packet forwarding can take place. • Convergence will not happen until all the routers have complete and accurate routing information, meaning we must configure static routes on all the routers before packets will be correctly delivered. 26

  27. Static Routing 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 Network/subnet route Intermediate-Address (usually “next-hop”) RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Serial0 S 192.168.1.0/24 [1/0] via 172.16.0.2 C 192.168.2.0/24 is directly connected, Ethernet0 Basic static route example • Be sure to use the proper subnet mask! 27

  28. Static Routing 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Serial0 S 192.168.1.0/24 [1/0] via 172.16.0.2 C 192.168.2.0/24 is directly connected, Ethernet0 Basic static route example (continued) • [1/0] – [ Administrative Distance / Metric ] • Administrative Distance – This is the “trustworthiness” of the routing information. The default administrative distance of static routes is 1. • The Administrative Distance of a directly connected route is 0. • Lower the AD the more trustworthy. • If the router learns about a route to a network from more than one source, it will install the route with the lower administrative distance in the routing table. 28

  29. Static Routing 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Serial0 S 192.168.1.0/24 [1/0] via 172.16.0.2 C 192.168.2.0/24 is directly connected, Ethernet0 Basic static route example (continued) • [1/0] – [ Administrative Distance / Metric ] • Metric – This is the “cost” of getting to this route, I.e. how far away this network is. • The lower the cost, the closer the network. • Static routes always show a cost of “0” even if it was configured with the intermediate address is multiple-hops away. • Much more later. 29

  30. Static Routing 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Serial0 S 192.168.1.0/24 [1/0] via 172.16.0.2 C 192.168.2.0/24 is directly connected, Ethernet0 2 1 Recursive Lookup • The router knows it can get to 192.168.1.0/24 network by forwarding the packets to the router at the ip address of 172.16.0.2 • How does the router know how to get to the ip address 172.16.0.2? • It does a recursive lookup – first (1) by looking up the 192.168.1.0/24 network and finding it needs to forward the packet to 172.16.0.2 – the router then (2) looks up the 172.16.0.0 network and sees it can forward it out the interface Serial 0. 30

  31. Static Routing 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA#debug ip routing IP routing debugging is on RTA#conf t Enter configuration commands, one per line. End with CNTL/Z. RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 05:53:48: RT: add 192.168.1.0/24 via 172.16.0.2, static metric [1/0] RTA(config)#ip route 10.1.0.0 255.255.0.0 172.16.0.2 05:54:38: RT: add 10.1.0.0/16 via 172.16.0.2, static metric [1/0] RTA(config)#undebug all Static Routes and the Routing Table Process • Notice that the static route is entered into the routing table by the routing table process (debug ip routing) with a metric of 0. 31

  32. Static Routing 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 RTA(config)#ip route 10.1.0.0 255.255.0.0 172.16.0.2 RTB(config)#ip route 192.168.2.0 255.255.255.0 172.16.0.1 RTB(config)#ip route 10.1.0.0 255.255.0.0 192.168.1.2 RTC(config)#ip route 192.168.2.0 255.255.255.0 192.168.1.1 RTC(config)#ip route 172.16.0.0 255.255.0.0 192.168.1.1 Configuring all of the static routes • Notice that the intermediate-address is always the next-hop ip address. • This does not always have to be the case, and we will look at other options in the presentation on Static Routes- Additional Information • Good idea to do a “copy running-config startup-config” if everything is working right. • To verify the routes are in there, you can do a: Router# show running-config 32

  33. Static Routing 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 RTA(config)#ip route 10.1.0.0 255.255.0.0 172.16.0.2 RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Serial0 10.0.0.0/16 is subnetted, 1 subnets S 10.1.0.0 [1/0] via 172.16.0.2 S 192.168.1.0/24 [1/0] via 172.16.0.2 C 192.168.2.0/24 is directly connected, Ethernet0 RTA#ping 10.1.0.1 !!!!! RTA#ping 192.168.1.2 !!!!! RTA#ping 192.168.1.1 !!!!! 33

  34. Static Routing – Recursive Lookups 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Serial0 S 192.168.1.0/24 [1/0] via 172.16.0.2 C 192.168.2.0/24 is directly connected, Ethernet0 2 1 Recursive Lookup • The router knows it can get to 192.168.1.0/24 network by forwarding the packets to the router at the ip address of 172.16.0.2 • How does the router know how to get to the ip address 172.16.0.2? • It does a recursive lookup – first (1) by looking up the 192.168.1.0/24 network and finding it needs to forward the packet to 172.16.0.2 – the router then (2) looks up the 172.16.0.0 network and sees it can forward it out the interface Serial 0. 34

  35. Static Routing – Recursive Lookups 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 10.1.0.0 255.255.0.0 192.168.1.2 RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Serial0 S 192.168.1.0/24 [1/0] via 172.16.0.2 S 10.1.0.0/16 [1/0] via 192.168.1.2 C 192.168.2.0/24 is directly connected, Ethernet0 3 2 1 Recursive Lookup (continued) • We can take this even further. • One route can be used to resolve the route of another. • It doesn’t matter how the routes are resolved, whether they are directly connected, static or dynamic. • Note: If an intermediate address cannot be resolved, that route and any routes it affects are not installed in the routing table. 35

  36. Static Routing – Recursive Lookups Note regarding recursive route lookups • Every route that does not reference an exit-interface must finally be resolved via a route with an interface descriptor reference in the corresponding path descriptor – a route with an exit-interface. • Static routes cannot be recursively resolved and will not be in the routing table. • Consider these three static routes: Route1: ip route 10.1.0.0 255.255.0.0 20.1.1.1 Route2: ip route 20.1.0.0 255.255.0.0 30.1.1.1 Route3: ip route 30.1.0.0 255.255.0.0 10.1.1.1 • • • • Route1 is resolved by Route2 which is resolved by Route3. None of these routes are finally resolved via a route with an exit-interface. This leads to endless recursion. The routing table process will not permit these static routes to be entered in the routing table. Note: Static default routes (coming soon) can never be resolved via another default route. (later) • 36

  37. Static Routing – Routing Table Process 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA#debug ip routing IP routing debugging is on RTA#conf t Enter configuration commands, one per line. End with CNTL/Z. RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 05:53:48: RT: add 192.168.1.0/24 via 172.16.0.2, static metric [1/0] RTA(config)#ip route 10.1.0.0 255.255.0.0 172.16.0.2 05:54:38: RT: add 10.1.0.0/16 via 172.16.0.2, static metric [1/0] RTA(config)#undebug all Static Routes and the Routing Table Process • Notice that the static route is entered into the routing table by the routing table process (debug ip routing) with a metric of 0. 37

  38. Static Routing – Point-to-Point Links 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 serial 0 RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Serial0 S 192.168.1.0/24 is directly connected, Serial0 C 192.168.2.0/24 is directly connected, Ethernet0 • • Need only to use only an exit interface. For point-to-point serial interfaces, the next-hop address in the routing table is never used by the packet-delivery procedure, so it is not needed. (It could even reference a bogus IP address.) Notice that the static route appears in the routing table as directly connected, however it is still a static route with an administrative distance of 1. • 38

  39. Static Routing – Point-to-Point Links 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC e0 s0 s0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 172.16.0.2 RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Serial0 S 192.168.1.0/24 [1/0] via 172.16.0.2 C 192.168.2.0/24 is directly connected, Ethernet0 2 1 Using an intermediate address instead of an exit-interface: • If an intermediate address is used on a static route via a point-to-point link, it is only used to find the exit-interface, • This recursive lookup is unnecessary and takes extra processing. 39

  40. Static Routing – Ethernet interfaces 192.168.2.0/24 172.16.0.0/16 192.168.1.0/24 10.1.0.0/16 RTA RTB RTC s0 e1 s0 e0 e0 s1 s1 e0 .1 .1 .2 .1 .2 .1 RTA(config)#ip route 192.168.1.0 255.255.255.0 eth 1 172.16.0.2 RTA#show ip route Codes: C - connected, S - static, C 172.16.0.0/16 is directly connected, Ethernet1 S 192.168.1.0/24 [1/0] via 172.16.0.2 Ethernet1 C 192.168.2.0/24 is directly connected, Ethernet0 Using both an intermediate address instead and an exit-interface: • Notice we changed 172.16.0.0 to an Ethernet link. • Static routes via broadcast links, it is best to use both an exit interface and intermediate address. • This saves the router from having to do a recursive route lookup for the intermediate address of 172.16.0.2, knowing the exit interface is Ethernet 0. 40

  41. Static Route Rule of Thumb Static routes via point-to-point links • It is best to configure static routes with only the exit interface. • For point-to-point serial interfaces, the next-hop address in the routing table is never used by the packet-delivery procedure, so it is not needed. (It could even reference a bogus IP address.) Static routes via broadcast networks such as Ethernet • It is best to configure static routes with both the next-hop address and the exit- interface. Using only an intermediate address • “What about static routes referencing only intermediate network address? In short, try to avoid using them. The reason is that these static routes are not bound to any interface, rely on intermediate address resolvability, and thus converge more slowly. They can also create unexpected routing loops.” Alex Zinin, Cisco IP Routing NOTE: Most of our examples in this course do not follow either of these rules-of- thumb – but you may want to use it on your network. 41

  42. Common uses for Static Routes Static routes in the real-world • Soon we will learn about dynamic routing protocols (RIP, etc.), where routers can learn automatically about networks, without the manual configuration of static routes. • Does this mean that static routes are never used in the real-world? • No! Static routes are used in conjunction with dynamic routing protocols. • It is common to use a static route where using a dynamic routing protocols would have disadvantages or where it just not needed. 42

  43. Common uses for Static Routes 10.1.1.1/24 ISP ip route 172.16.0.0 255.255.0.0 10.1.1.2 10.1.1.2/24 Cabrillo College 172.16.0.0/16 Static routes in the real-world (continued) • In the example above, there is only one route, link, between Cabrillo College’s network and the ISP. • When there is only a single route to a network, this is known as a stub network. • It is very common for the ISP to have a static route pointing to it’s customers’ networks, in this case Cabrillo College. 43

  44. Common uses for Static Routes Default 10.1.1.1/24 ISP ip route 172.16.0.0 255.255.0.0 10.1.1.2 10.1.1.2/24 Cabrillo College 172.16.0.0/16 ip route 0.0.0.0 0.0.0.0 10.1.1.1 Static routes in the real-world (continued) • What about Cabrillo College and sending packets to the ISP – packets going to the Internet? • It is also common for customer networks to use a special kind of static route, known as a default static route. • Of course we will examine this later throughout the rest of this course, but for now we specify the network and mask as “0.0.0.0 0.0.0.0” (pronounced “quad-zero”). • This tells the router to forward all packets to this next-hop address (or exit interface) that do not have an explicit route in the routing table. 44

  45. Common uses for Static Routes Default 10.1.1.1/24 ISP ip route 172.16.0.0 255.255.0.0 10.1.1.2 10.1.1.2/24 Cabrillo College 172.16.0.0/16 ip route 0.0.0.0 0.0.0.0 10.1.1.1 RTB#show ip route Gateway of last resort is 10.1.1.1 to network 0.0.0.0 C 172.16.0.0/16 is directly connected, Ethernet0 10.0.0.0/24 is subnetted, 1 subnets C 10.1.1.0 is directly connected, Serial1 S* 0.0.0.0/0 [1/0] via 10.1.1.1 • Any packets not matching the routes 172.16.0.0/16 or 10.1.1.0/24 are sent to the router 10.1.1.1 – where it is now their “problem.” 45

  46. Summarizing static routes • There are many times when a single static route can replace several static routes. In other words, summarizing several static routes into a single static route. • 172.16.0.0/24 46

  47. Summarizing static routes 172.16.0.0/24 Baypointe • Let’s configure three static routes on Baypointe using either an intermediate-address or exit interface: Baypointe(config)# ip route 172.16.1.0 255.255.255.0 192.168.1.2 Baypointe(config)# ip route 172.16.2.0 255.255.255.0 192.168.1.2 Baypointe(config)# ip route 172.16.3.0 255.255.255.0 192.168.1.2 47

  48. Summarizing static routes Baypointe • The three static routes can be summarized into a single route: Baypointe(config)# ip route 172.16.1.0 255.255.255.0 192.168.1.2 Baypointe(config)# ip route 172.16.2.0 255.255.255.0 192.168.1.2 Baypointe(config)# ip route 172.16.3.0 255.255.255.0 192.168.1.2 • Summarized route: Baypointe(config)# ip route 172.16.0.0 255.255.0.0 192.168.1.2 • • • The summarized route will now include all three subnets! Be sure to use the proper mask – 255.255.0.0! Using a 255.255.255.0 mask will only route for 172.16.0.0/24 subnet and not 172.16.1.0/24, 172.16.2.0/24 or 172.16.3.0/24. 48

  49. Summarizing static routes 172.16.0.0/24 Baypointe • Summarized route: Baypointe(config)# ip route 172.16.0.0 255.255.0.0 192.168.1.2 Advantages: • Fewer routes in the routing table – faster routing table lookup. • Subnets can be added and deleted on 172.16.0.0 network without having to change static route on Baypointe router. 49

  50. Verify static routes Copy running-config startup-config 50

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