INTERNET LABORATORY PROJECT. EIGRP Routing Protocol. Abhay Tambe Aniruddha Deshmukh Sahil Jaya

Transcription

1 INTERNET LABORATORY PROJECT on EIGRP Routing Protocol by Abhay Tambe Aniruddha Deshmukh Sahil Jaya

2 INTRODUCTION TO EIGRP SETUP FOR LAB: This lab uses two different network topologies. The first network topology is shown in Figure 1and is used in parts 1 and 2 and another topology is shown in Figure 2 and used in parts 3 and 4. PART 1. CONFIGURING EIGRP ON A CISCO ROUTER Enhanced Interior Gateway Routing Protocol (EIGRP) is an interior gateway protocol suited for many different topologies and media. In a well-designed network, EIGRP scales well and provides extremely quick convergence times with minimal network traffic. Enhanced Interior Gateway Routing Protocol - (EIGRP) is an open routing protocol loosely based on their original IGRP created by Cisco. EIGRP is an advanced distance-vector routing protocol, with optimizations to minimize both the routing instability incurred after topology changes, as well as the use of bandwidth and processing power in the router. Routers that support EIGRP will automatically redistribute route information to IGRP neighbors by converting the 32 bit EIGRP metric to the 24 bit IGRP metric. Most of the routing optimizations are based on the Diffusing Update Algorithm (DUAL) work from SRI, which guarantees loop-free operation and provides a mechanism for fast convergence. Figure 1 and Table 1 describe the network configuration for this part of the lab. Contiguous network: A single classful network in which packets sent between every pair of subnets will pass only through subnets of that same classful network, without having to pass through subnets of any other classful network. For example: Discontiguous network: A single classful network in which packets sent between at least one pair of subnets must pass through subnets of a different classful network. For example:

3 Route Filtering: EIGRP support for route map filtering enables EIGRP to interoperate with other protocols by filtering inbound and outbound traffic based on route map options. Additional EIGRP-specific match choices are available to allow flexibility in fine-tuning EIGRP network operations. EIGRP supports the route map filtering capability that exists for other routing protocols to filter routes being redistributed into their protocol. For more details about understanding and configuring route maps. Match options allow EIGRP to filter internal and external routes based on source protocols, to match a metric against a range, and to match on an external protocol metric. EIGRP can be configured to filter traffic using a route map and the redistribute or distribute-list command. Using a route map with the redistribute command allows routes that are redistributed from the routing table to be filtered with a route map before being admitted into an EIGRP topology table. Routes that are dynamically received from, or advertised to, EIGRP peers can be filtered by adding a route map option to the distribute-list command. Authentication: The addition of authentication to your routers' EIGRP messages ensures that your routers only accept routing messages from other routers that know the same pre-shared key. Without this authentication configured, if someone introduces another router with different or conflicting route information on to the network, the routing tables on your routers could become corrupt and a denial of service attack could ensue. Thus, when you add authentication to the EIGRP messages sent between your routers, it prevents someone from purposely or accidentally adding another router to the network and causing a problem. The configuration of EIGRP message authentication consists of two steps: 1. The creation of a keychain and key. 2. The configuration of EIGRP authentication to use that keychain and key. Once you create a keychain and key, you must configure EIGRP to perform message authentication with the key. This configuration is completed on the interfaces that EIGRP is configured on. EIGRP Neighborship: EIGRP uses three major steps to achieve its goal of learning the best available loop-free routes: Step 1. Establish EIGRP neighbor relationships neighborships with other routers that share a common subnet. Step 2. Exchange EIGRP topology data with those neighbors. Step 3. Calculate the currently best IP route for each subnet, based on the known EIGRP topology data, and add those best routes to the IP routing table. This three-step process hinges on the first step the successful creation of neighbor relationships between EIGRP routers. The basic EIGRP configuration described earlier in this chapter, particularly the network command, most directly tells EIGRP on which interfaces to dynamically discover neighbors. After EIGRP neighborships have been formed with neighboring routers that are reachable through those interfaces, the final two steps occur without any additional direct configuration. EIGRP dynamically discovers neighbors by sending EIGRP Hello messages on each EIGRP-enabled interface. When two routers hear EIGRP Hello messages from each other, they check the EIGRP parameters listed in those messages and decide whether the two routers should or should not become neighbors. Hello interval: Interval at which a router sends EIGRP Hello messages on an interface. Hold Timer: Timer used to determine when a neighboring router has failed, based on a router not receiving any EIGRP messages, including Hellos, in this timer period. The basic operation of these two timers is relatively simple. EIGRP uses the Hello messages in part as a confirmation that the link between the neighbors still works. If a router does not receive a Hello from a neighbor for one entire Hold time, that router considers the neighbor to have failed. For example, with a default LAN setting of Hello of 5, and Hold of 15, the local router sends Hellos every 5 seconds. The neighbor resets its downward-counting Hold Timer to 15 upon receiving a Hello from that neighbor. Under normal

4 operation on a LAN, with defaults, the Hold Timer for a neighbor would vary from 15, down to 10, and then be reset to 15. However, if the Hellos were no longer received for 15 seconds, the neighborship would fail, driving convergence. Convergence: The word convergence defines the overall process by which routers notice internetwork topology changes, communicate about those changes, and change their routing tables to contain only the best currently working routes. EIGRP converges very quickly even with all default settings. EIGRP converges very quickly, but EIGRP does not achieve the most optimal fast convergence times in all conditions. One design goal might be to tune EIGRP configuration settings so that EIGRP uses the faster convergence methods for as many routes as possible, and when not possible, that EIGRP converge as quickly as it can without introducing routing loops. As a result, routers might converge in some cases in a second instead of tens of seconds (from the point of a router realizing that a route has failed). Default Routing: A router s default route matches the destination of all packets that are not matched by any other route in the IP routing table. In fact, a default route can be thought of as the ultimate summary route a route for the prefix that includes all IPv4 addresses, as represented by prefix/length /0. This section first examines the most common use of default routes inside an Enterprise: to draw Internet traffic toward the Internet-connected routers without having to put routes for all Internet destinations into the Enterprise routers routing tables Default Routing Configuration with EIGRP: 1. Advertising Static Default Routes with EIGRP To cause the advertisement of the default routes shown in Figure 4-9, Router I1 can follow these steps: Step 1. Create a static route default route using the ip route S0/0/0 command. Step 2. Inject this route into the EIGRP topology database, either using the network command or by redistributing the static route. 2. Configuring a Default Network The second option for creating a default route is to flag a route for a classful network for a prefix that will be advertised into the EIGRP domain as a route that can be used as a default route. Then each router can use the forwarding details in that route the outgoing interface and next-hop router as its default route. Step 1. On the router to which all traffic should be directed, identify a classful network that can be advertised into the EIGRP domain, and ensure that network is being advertised into EIGRP (typically using the EIGRP network command). Step 2. Configure that network as a default network using the global command ip default network networknumber. Load Balancing: IOS allows routing protocols to place multiple routes into the routing table for an individual prefix/length. IOS then balances traffic across those routes, by default balancing traffic on a per-destination IP address basis. Load balancing, sometimes called load sharing, provides a primary benefit of making use of the available bandwidth, rather than using some links as simply backup links. A useful secondary benefit faster convergence occurs when using load balancing. By placing multiple routes into the routing table for a single prefix, convergence happens essentially instantly. For example, if a branch router has two routes for each data center subnet one using each PVC that connects the branch to the core and one of the routes fails, the other route is already in the routing table. In this case, the router does not need to look for FS routes nor go active on the route. The router uses the usual EIGRP convergence tools only when all such routes are removed from the routing table. The load balancing configuration requires two commands, one of which already defaults to a reasonable setting. First, you need to define the number of allowed routes for each prefix/prefix length using the maximum-paths number EIGRP subcommand. The default setting of 4 is often big enough, because most internetworks do not have enough redundancy to have more than four possible routes. The second part of the load balancing configuration overcomes a challenge introduced by EIGRP s metric calculation. The EIGRP integer metric calculation often results in 8-to-10- digit integer metrics, so the metrics of competing routes are seldom the exact same value. Calculating the exact same metric for different routes for the same prefix is statistically unlikely. IOS includes the concept of EIGRP variance to overcome this problem. Variance lets you tell IOS that the EIGRP

5 metrics can be close in value and still be considered worthy of being added to the routing table and you can define how close. The variance multiplier EIGRP router subcommand defines an integer between 1 and 128. The router then multiplies the variance times the successor route s FD the metric of the best route to reach that subnet. Any FS routes whose metric is less than the product of the variance times the FD are considered to be equal routes and may be placed into the routing table, up to the number of routes defined by the maximum-paths command. Metric Calculations: EIGRP associates six (6) different vector metrics with each route and considers only four (4) of the vector metrics in computing the Composite metric: Bandwidth: Minimum Bandwidth (in kilobits per second) along the path from router to destination network Load: Load (number in range 1 to 255; 255 being saturated) Delay: Total Delay (in 10s of microseconds) along the path from router to destination network Reliability: Reliability (number in range 1 to 255; 255 being the most reliable) MTU: Minimum path Maximum Transmission Unit (MTU) (never used in the metric calculation) Hop Count: Number of routers a packet passes through when routing to a remote network, used to limit the EIGRP AS. The K Values There is five (5) K values used in the Composite metric calculation - K1 through K5. The K values only act as multipliers or modifiers in the composite metric calculation. K1 is not equal to Bandwidth, etc. By default, only total delay and minimum bandwidth are considered when EIGRP is started on a router, but an administrator can enable or disable all the K values as needed to consider the other Vector metrics. For the purposes of comparing routes, these are combined together in a weighted formula to produce a single overall metric: where the various constants ( through ) can be set by the user to produce varying behaviors. An important and unintuitive fact is that if is set to zero, the term is not used (i.e. taken as 1). The default is for and to be set to 1, and the rest to zero, effectively reducing the above formula to. Obviously, these constants must be set to the same value on all routers in an EIGRP system, or permanent routing loops will probably result. Cisco routers running EIGRP will not form an EIGRP adjacency and will complain about K- values mismatch until these values are identical on these routers. EIGRP scales the interface bandwidth and delay configuration values with following calculations: = 10 7 / Value of the bandwidth interface command = Value of the delay interface command

6 PRELAB QUESTIONS FOR EIGRP LAB Q1. What type of routing protocol is EIGRP. Give one advantage and disadvantage of EIGRP. Q2. What is the default method of calculating metrics for routes in EIGRP? Q3. Explain the tems Feasible Distance and Reported Distance Q4. Explain discontiguous networks. Q5. Explain neighborship in EIGRP Q6. Explain convergence in EIGRP. Q7. How does EIGRP perform load balancing. Q8. Explain what are access lists and what are their uses. Q9. Explain route filtering and route summarization. Q10. How are default routes added and distributed via EIGRP.

7 LAB EXERCISE 1 Configuration and Neighborship. Figure 1 : Topology for Lab Exercise 1 and 2 The topology for parts is shown in figure 1. CONFIGURATION OF EIGRP 1 (A): Setting Up The Network. Step 1. Set up the network as shown in the figure. Step 2. Make sure that the local interfaces can be pinged by the ping command. Step 3. Enter the following commands on both the routers: no ip routing ip routing 1 (B): Configuring EIGRP Step 1. Run the following commands on both the routers in global configuration mode. router eigrp 10 passive- interface eth 0 network network exit Step 2. Run the folowing commands: Ping from and vice versa. Ping from and vice versa. Ping from and vice versa.

8 Ping from and vice versa. QUESTIONS: 1. Which of the pings were successful and which were not? 2. Explain your reasoning. 3. What does the passive interface command do? Why is it necessary? 1 (C): Configuring EIGRP For Discontinuous Networks. Step 1: On both routers, enter the following commands in global configuration mode: router eigrp 10 no auto-summary exit Step 2. Try the same set of pings and observe the output. QUESTIONS: 1. Why did the pings work now? Explain what the no auto-summary command does. 2. Can you show how the metric was calculated for routing between the two routers? 1 (D): Observing neighborship formation. NEIGHBORSHIP Step 1. Run the follwing command on both routers in privilege mode and observe the output show ip eigrp interfaces detail serial 0 Step 2. Note down the Hello Interval of both the routers. Step 3. Run the following command on both routers in privilege and observe the output. show ip eigrp neighbors. Step 4. Repeat step 3 many times and try and estimate the hold time from the various outputs and from Hello Interval. QUESTIONS(1): 1. What was the configured Hello Interval? 2. What was the configured Hold Time? How could you tell? 3. Explain the first 6 columns in the output of Step 3. 1 (E): Changing The Neighborship Parameters. Step 1. On Router 1, enter the following commandsin global configuration mode: interface serial 0 ip hello-interval eigrp 10 2 ip hold-time eigrp 10 6

9 Step 2. Run show ip eigrp interfaces detail serial 0 and show ip eigrp neighbors command to confirm changes. QUESTIONS(2): 1. Explain one advantage of changing these configuration parameters.

10 LAB EXERCISE 2 ROUTE FILTERING via EIGRP The topology for this part is the same as the topology in Lab Exercise One. However, restart all PC s and Routers so that the previous EIGRP Configurations are no longer valid. 2(A): Configuring Loopback Addresses Step 1: On Router 2, enter the following commands in global configuration mode. interface loopback 5 ip address interface loopback 6 ip address interface loopback 7 ip address interface loopback 8 ip address interface loopback 9 ip address interface loopback 10 ip address interface loopback 11 ip address (B): Creating Access Lists Step 1. On Router 2, create an access list by entering the following commands: access-list 2 deny access-list 2 deny

11 access-list 2 deny access list 2 permit any. 2(C): Distributing Routes via EIGRP Step 1. On Router 2, enter the following commands in global configuration mode. router eigrp 10 network network distribute-list 2 out no auto-summary exit Step 2. Configure EIGRP on Router 1 as was done in Lab Exercise One. QUESTIONS(1): 1. What entries do you see in Router 1 s routing table? 2. Explain why certain routes are present and some are missing? Why is route filtering done? 3. Can you atleast ping the missing routes? 4. Explain the advantags and disadvantages of route filtering and suggest any alternatives to this.

12 LAB EXERCISE 3 Convergengce and Load Balancing Figure 2. Topology for Parts 3 and 4 CONVERGENCE 3(A1) : Convergence With Known Feasible Successor Step 1. Set up the topology as shown in Figure 2. Do remember to add a default gateway on PC1. Step 2. Enter the following steps on all routers: (config)# router eigrp 20 network no auto-summary. Step 3. Ping acorss all interfaces from every router to ensure connectivity across the entire network. Step 4. Run the command show ip eigrp topology. Notice the path Router 1 takes to reach network address It can be seen that it takes the path via Router 2 since it is the lower cost path. It can also be seen that the path lists a feasible successor. Step 5. Start ethereal on interface eth0 of PC1. Set up a continuous ping from PC1 to Disconnect interface eth0 on router 1. The ping should be unsuccessful for some moments. From ethereal, note down the time taken for the network to converge. Reconnect interface eth0 on router 1.

13 Step 6. Check if connecting the interface again leads to change in the path again. 3 (A2) : Convergence With No Feasible Successor Step 1. Run the command show ip eigrp topology Note down the path Router 1 takes to reach network address Note down if the path to has any successor. There shouldn t be any. Step 2. Start ethereal on interface eth0 of PC1. Step 3. Start a continuous ping from PC1 to network address Disconnect eth0 of Router 1. On ethereal, observe how long it takes for ping to be successful again. Reconnect eth0 on router 1. Run traceroute to the same network address and check the path. QUESTIONS(1): 1. In which case did convergence take more time 2. Explain why you observe the difference in convergence times. 3. Explain Feasible Distance and Reported Distance 3 (B1) : Load Balancing Across Equal Links. LOAD BALANCING Step 1. On Router 3 run the following command in global configuration mode. router eigrp 20 maximum-paths 4. variance 1. Step 2. Run the command sh ip route on Router 3 The path to network shoud list two routes. Observe that the routes are the exact same cost. Comfirm the load balancing by executing traceroute to from Router 3. Step 3. Repeat step 1, but this time change the variance to 50. Run sh ip route and see if there are any other changes. QUESTIONS(2): 1. What is the necessary condition for load balancing? 2. What do the maximum-paths 4 and variance 1 command do?

14 3. Explain your observation in step 3. 3 (B2) : Load Balancing Across Un-Equal Links. Step 1. On Router 1, run the command sh ip eigrp topology and save the output. Observe the entry for network lists two successors. Step 2. On Router 1, run the command sh ip route and save the output. Step 3. On Router 1, run the following commands in global configuration mode. router eigrp 20 maximum paths 4 variance 2. Step 4. On Router 1, run the command sh ip route and save the output. Step 5. repeat step 4 and this time and change the variance value to 50. Run sh ip route and observe the output. QUESTIONS(3): 1. What does the variance 2 command do? 2. Explain your observation in step 5.

15 LAB EXERCISE 4 Adding and Distributing Default Route with EIGRP We use the same topology as in part 2 for this experiment. 4(A): Step 1: On Router 4, add the following commands in global configuration mode: interface loopback 8 ip address exit router eigrp 1 network no auto-summary. exit ip default network Step 2. Run the command sh ip route on all routers and observe the output. QUESTIONS(1): 1. Explain the difference between this route entry and other routes in the table.