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Giao thức định tuyến - Chapter 7

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Encounter a d desc be the limitations o RIPv1’s cou e and describe e a o s of s limitations. Apply the basic Routing Information Protocol Version 2 (RIPv2) configuration commands and evaluate RIPv2 classless routing updates. Analyze router output to see RIPv2 support for VLSM and CIDR Identify RIPv2 verification commands and common RIPv2 issues.

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Nội dung Text: Giao thức định tuyến - Chapter 7

  1. RIPv2 Routing Protocols and Concepts – Chapter 7 ITE PC v4.0 1 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  2. Objectives Encounter and describe the limitations of RIPv1’s cou desc limitations. Apply the basic Routing Information Protocol Version Apply the basic Routing Information Protocol Version 2 (RIPv2) configuration commands and evaluate RIPv2 classless routing updates. Analyze router output to see RIPv2 support for VLSM and CIDR Identify RIPv2 verification commands and common RIPv2 issues. Configure, verify, and troubleshoot RIPv2 in “hands- on” labs ITE PC v4.0 2 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  3. Introduction Introduction Difference between RIPv1 & RIPv2 RIPv1 •A classful distance vector routing protocol •Does not support discontiguous subnets not support discontiguous subnets •Does not support VLSM •Does not send subnet mask in routing update •Routing updates are broadcast RIPv2 •A classless distance vector routing protocol that is an enhancement of RIPv1 features enhancement of RIPv1’s features. http://www.cisco.com/univercd/cc/t •Next hop address is included in updates d/doc/cisintwk/ito_doc/rip.htm •Routing updates are multicast (224.0.0.9 vs. 255.255.255.255) •The use of authentication is an option ITE PC v4.0 3 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  4. Introduction Similarities between RIPv1 & RIPv2 – Use of timers to prevent routing loops of timers to prevent routing loops – Use of split horizon or split horizon with poison reverse to also help prevent routing loops. – Use of triggered updates when there is a change in the topology for faster convergence. – Maximum hop count of 15, with the hop count of 16 signifying hop count of 15 with the hop count of 16 signifying an unreachable network. ITE PC v4.0 4 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  5. RIP Li RIPv1 Limitations Lab Topology 3 router set up Topology is discontiguous There exists a static summary route Static route information can be injected into routing table updates using redistribution. Routers Routers 1 & 3 contain VLSM contain VLSM networks Remember that both the R1 and R3 routers have subnets that are part of the 172 the 172.30.0.0/16 major classful major classful network (class B). Also remember that R1 and R3 are connected to R2 using subnets of the 209.165.200.0/24 major classful network (class C). This topology is discontiguous and will not converge because will not converge because 172.30.0.0/16 is divided by the 209.165.200.0/24. ITE PC v4.0 5 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  6. RIP Li RIPv1 Limitations The topology shows that R2 has static R2 has a static summary route to the 192.168.0.0/16 network. The configuration of this summary route will be displayed later in this section. ITE PC v4.0 6 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  7. RIP Li RIPv1 Limitations Review the VLSM addressing scheme in the figure As shown scheme in the figure. As shown in the top chart, both R1 and R3 have had the 172.30.0.0/16 network subnetted into /24 subnets subnets. –Four of these /24 subnets are assigned: –two to R1 (172.30.1.0/24 and 172.30.2.0/24) –two to R3 (172.30.100.0/24 and 172.30.110.0/24). In the bottom chart, we have th taken the 172.30.200.0/24 subnet and subnetted it again, using the first four bits for subnets and the last four bits for hosts. The result is a 255.255.255.240 mask or /28. Subnet and Subnet are Subnet 1 and Subnet 2 are assigned to R3. ITE PC v4.0 7 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  8. RIP Limitations RIPv1 Limitations Scenario Continued VLSM -Recall this is sub netting the subnet Private IP addresses are on LAN links Public IP addresses are used on WAN links (through an ISP, or when inside users need to access outside sites, a public IP address must be used.) Loopback interfaces -These are virtual interfaces that can be pinged and that can be pinged and added to routing table Cisco has set these addresses aside for educational purposes. ITE PC v4.0 8 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  9. RIPv1 Limitations Loopback interfaces Notice that R3 is using loopback interfaces (Lo0, Lo1, and Lo2). A loopback interface is a software-only interface that is used to emulate physical interface is used to emulate a physical interface. Like other interfaces, it can be assigned an IP address. Loopback interfaces are also used by other routing protocols, such as OSPF, for different purposes. These uses will be discussed in Chapter 11 OSPF. In a lab environment, loopback interfaces are useful in creating additional networks without having to add more physical interfaces on the router more physical interfaces on the router. A loopback interface can be pinged and the subnet can be advertised in routing updates. Therefore, loopback interfaces are ideal for Therefore, loopback interfaces are ideal for simulating multiple networks attached to the same router. In our example, R3 does not need four LAN interfaces to demonstrate multiple subnets and interfaces to demonstrate multiple subnets and VLSM. Instead, we use loopback interfaces. ITE PC v4.0 9 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  10. RIPv1 Limitations RIPv1 Limitations Route redistribution – Redistribution involves taking the routes from one routing involves taking the routes from one routing source and sending those routes to another routing source. • In our example topology, we want the RIP process on R2 to redistribute our static route (192.168.0.0/16) by importing the route into RIP and then sending it to R1 and R3 using the RIP process. -R2(config-router)#redistribute static ITE PC v4.0 10 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  11. RIPv1 Limitations RIPv1 Limitations R2(config)#ip route 192.168.0.0 255.255.0.0 Null0 –The address space represented by the static summary route address space represented by the static summary route 192.168.0.0/16 does not actually exist. –In order to simulate this static route, we use a null interface as the exit interface. – You do not need to enter any commands to create or configure the null interface configure the null interface. –It is always up but does not forward or receive traffic. Traffic sent to the null interface is discarded. ITE PC v4.0 11 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  12. Static routes and null interfaces Stat Static routes and null interfaces R2(config)#ip route 192.168.0.0 255.255.0.0 Null0 a static route must have an active exit interface static route must have an active exit interface before it will be installed in the routing table. Using the null interface will allow R2 to advertise the static route in RIP even though networks belonging to the summary 192.168.0.0/16 do not actually exist. ITE PC v4.0 12 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  13. Verifying and Testing Connectivity show ip interfaces brief –To test whether or not the topology has full th connectivity, we first verify that both serial links on R2 are up using the show ip interface brief Ping Whenever R2 pings any of the 172.30.0.0 subnets on R1 or R3, only about 50% of the ICMP are successful. R1 is able to ping 10.1.0.1 but is unsuccessful when attempting to ping the 172.30.100.1 on R3 R3 is able to ping 10.1.0.1 but is unsuccessful is able to ping 10 but is unsuccessful when attempting to ping the 172.30.1.1 on R1. ITE PC v4.0 13 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  14. RIP Li RIPv1 Limitations RIPv1 – a classful routing protocol –Subnet mask are not sent in updates mask are not sent updates –Summarizes networks at major network boundaries –RIPv1 cannot support discontiguous networks, VLSM, or CIDR. –if network is discontiguous and RIPv1 configured convergence will not be if di RIP reached –RIPv1 on both the R1 and R3 routers will summarize their 172.30.0.0 subnets to the classful major network address of 172 subnets to the classful major network address of 172.30.0.0 when sending when sending routing updates to R2. –From the perspective of R2, both updates have an equal cost of 1 hop to reach network 172 reach network 172.30.0.0/16. As you will see, R2 installs both paths in the you will see R2 installs both paths in the routing table. ITE PC v4.0 14 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  15. RIP Li RIPv1 Limitations Examining the routing tables -To examine the contents of routing updates use the debug ip rip command R2 is receiving two 172.30.0.0 equal cost 172 routes with a metric of 1 hop. R2 is R2 has two equal cost routes to the receiving one route on Serial 0/0/0 from R1 172.30.0.0/16 network. and the other route on Serial 0/0/1 from R3. ITE PC v4.0 15 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  16. RIP Li RIPv1 Limitations •R1 has its own 172.30.0.0 routes: has its own 172 routes: 172.30.2.0/24 and 172.30.1.0/24. •But R1 does not send R2 those subnets. •R3 has a similar routing table. •Both R1 and R3 are boundary routers and R1 R3 •R2 that it is not including the 172.30.0.0 network are only sending the summarized in its updates to either R1 or R3. 172.30.0.0 network to R2 in their RIPv1 •Because the split horizon rule is in effect. routing updates. •R2 learned about 172.30.0.0/16 on both the learned about 172 on both the •As a result, R2 only knows about the R2 th Serial 0/0/0 and Serial 0/0/1 interfaces, it does not 172.30.0.0/16 classful network and is include that network in updates it sends out these unaware of any 172.30.0.0 subnets. same interfaces. ITE PC v4.0 16 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  17. RIPv1 Limitations RIPv1 Limitations Because RIPv1 does not send the subnet mask in routing updates, it R4 is added to R4 is added to cannot support VLSM. the topology R3 router is configured with VLSM connected to R3 subnets all of which are members subnets, all of which are members of the class B network 172.30.0.0/16: –172.30.100.0/24 (FastEthernet 0/0) (FastEthernet 0/0) –172.30.110.0/24 (Loopback 0) –172.30.200.16/28 (Loopback 1) –172.30.200.32/28 (Loopback 2) (L 2) As we saw with the 172.30.0.0/16 updates to R2 by R3, –RIPv1 either summarizes the subnets to the classful boundary –or uses the subnet mask of the o sub outgoing interface to determine which subnets to advertise. ITE PC v4.0 17 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  18. RIPv1 Limitations RIPv1 Limitations Why is RIPv1 on R3 not including the other subnets, R4 is added to is added to 172 172.30.200.16/28 and and the topology 172.30.200.32/28, in updates to R4? connected to R3 – Those subnets do not have the subnets do not have the same subnet mask as FastEthernet 0/0. – R3 will only include those 172 172.30.0.0 routes in its routing routes in its routing table with the same mask as the exit interface. – Since the interface is 172.30.100.1 with a /24 mask, it will only include ith /24 it 172.30.0.0 subnets with a /24 mask. The only one that meets this condition is 172.30.110.0. – The other 172.30.0.0 subnets, 172.30.200.16/28 and 172.30.200.32/28, are not included because the /28 masks do not match the /24 mask of the outgoing interface. ITE PC v4.0 18 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  19. RIP Li RIPv1 Limitations No CIDR Support R2(config)#ip route 192.168.0.0 route 192 255.255.0.0 Null0 –the static route is included in R2's routing table, but R2 will not include the static route in its not include the static route in its update –R1 is not receiving this 192.168.0.0/16 route in its RIP updates from R2, Reason: Classful routing protocols do not support CIDR routes that are summarized with a smaller mask than the classful subnet mask –If the 192.168.0.0 static route were configured with a /24 mask or greater, this route would be included in the RIP updates. ITE PC v4.0 19 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  20. Config Configuring RIPv2 RIP Comparing RIPv1 & RIPv2 Message Formats –RIPv2 Message format is similar to RIPv1 but has 2 extensions 1st extension is the subnet mask field allows a 32 bit mask to be included in the RIP route entry. the receiving router no longer depends upon the subnet mask of the the receiving router no longer depends upon the subnet mask of the inbound interface or the classful mask when determining the subnet mask for a route 2nd extension is the addition of next hop address The Next Hop address is used to identify a better next-hop address - if one exists - than the address of the sending router. If the field is set to all zeros (0.0.0.0), the address of the sending router is the best next is the best next-hop address. address ITE PC v4.0 20 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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