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C C N A  Day2
 

C C N A Day2

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C C N A Day2

C C N A Day2

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  • great explanation!
    would be nice to update by adding EIGRP to IGRP even thought is no longer running on the newer IOS versions.
    IGRP-routed packets 255 default 100
    EIGRP hop count 224 default 100
    convergence 3 seconds
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  • informative
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  • very good
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  • Function POST Bootstrap
  • Function POST Bootstrap
  • Enable router to connect other devices Based on the type we have modular and non modular Non modular are fixed Modular can be added interfaces Ethernet or FA – connecting to switch Line – for the local configuration Router – console port PC- Serial Port Aux – for remote configuration using a modem BRI – for ISDN WAN connectivity Ports are numbered serially
  • Note: RAM—Packet buffers, running configurations, running Cisco IOS ROM—POST, ROM monitor, baby Cisco IOS (Rxboot) NVRAM—Backup configurations, config register Flash—Cisco IOS Flash memory is nonvolatile. It behaves like a file system. It is more expensive than NVRAM. It is readable and writeable. The 2500 routers run from Flash. If it is running Cisco IOS from Flash, then the Flash is in the readable state. Use the boot system command to boot Cisco IOS from a TFTP server so the 2500 can run from RAM if you need to write or erase Flash online.
  • Emphasize: In a later slide, there is a very detailed flowchart of the router startup process.
  • Rommonitor – Safe Mode Rxboot – TFTP Server Flash
  • Note: The 2500 series routers do not operate this way. The 2500 series routers normally run Cisco IOS from Flash. The Cisco IOS in Flash is not compressed but it is relocatable. Relocatable means the Cisco IOS image can be run from Flash or from RAM. The 2500 can run from RAM if you use the boot system tftp command to boot the Cisco IOS image. The Rxboot mode is also run from RAM on the 2500 routers.
  • Emphasize: Using the default config register value (0x2102), the router will load the config from NVRAM at startup.
  • Purpose: This slide presents the show version command. Emphasize: Point out that this command is useful when troubleshooting problems because it gives the versions of the various software components and files. It also displays how long the router has been in operation and where it obtained the image file. Config register is discussed in Chapter 6, “Catalyst Switch Operations.”
  • Emphasize: When you exit the setup mode, the configuration can be saved to RAM and NVRAM at the same time. Note: The Catalyst 1900 has no show start command. It automatically saves the running configuration to NVRAM.
  • Purpose: This slide shows the format and output of the show running-config and show startup-config commands, which display the active and backup configuration files, respectively. Emphasize: We put these two commands on the same page because it is easy to confuse the two. The show running-config command displays the configuration information in memory, while the show startup-config command displays the backup file. Often in class someone will enter commands and then say that the router did not accept them. This scenario might indicate that the person entered the commands to modify the configuration information in memory, and then entered a show startup-config (show config) to look at the backup file that has not yet been updated to reflect the changes. You must use another command to update the backup file. Default parameters do not display in the running configuration. In Cisco IOS Release 10.2 and earlier, the write terminal command shows the running configuration, and the show config command shows the startup configuration.
  • As its name suggests, the most common use of the show version command is to determine which version of the Cisco IOS a device is running. However, this command does much more than that—it actually offers several different uses. Let David Davis introduce you to the many uses of Cisco's show version command, and see how its output varies according to which device you're using. 1. The version of the IOS operating system 2. The version of the ROM bootstrap 3. The version of the boot loader 4. How someone last powered on the device (In addition to powering on in the usual manner, you can also power on a device with a system reset (i.e., warm reboot) or by a system panic.) 5. The time and date the system last started 6. The "uptime" for the system (i.e., how much time has passed since the last power-on) 7. The image file that the device last started (i.e., the actual path to the IOS software) 8. How much RAM the device has 9. The processor board ID, which you can use to determine the version of the device's motherboard 10. The number and type of each interface on the device (e.g., Qty 2 Ethernet, Qty 6 Serial, etc.) 11. The number of terminal lines on the router if a router has asynchronous serial lines attached 12. The amount of nonvolatile RAM (NVRAM), used to hold the SAVED version of the configuration file, also known as the startup-configuration 13. The amount and type of Flash on the device (except on a switch), used to hold the operating system when it isn't in use (Think of it as the equivalent to a hard drive on a PC.) 14. The configuration register on the device, which is a hexadecimal number used to tell the device what to do when it boots. (Typically, this only changes when you need to bypass the configuration file because of a lost password, but you can also change it for other special cases.) 15. The hostname of the device SHOW HISTORY will give all commands available in history bufer By default the buffer size is 10, this can be seen by SHOW TERMINA: Command The terminal history size can be increased by #Terminal History size 25
  • Connecting to the Auxiliary Port When a modem is connected to the auxiliary port, a remote user can dial in to the router and configure it. Use the light blue console cable and the DB-9-to-DB-25 connector adapter that came in the router accessory kit. To connect a modem to the router, follow these steps: Step 1- Connect the RJ-45 end of the adapter cable to the black AUX port on the router. Step 2-Connect the DB-9 end of the console cable to the DB-9 end of the modem adapter. Step 3-Connect the DB-25 end of the modem adapter to the modem.
  • The router Serial to serial AUI to Host Change Host name to R1 AND R2
  • To see the route #Show IP route
  • Purpose: this figure states the chapter objectives. Emphasize: Read or state each objective so each student has a clear understanding of the chapter objectives.
  • In internetworking , the process of moving a packet of data from source to destination . Routing is usually performed by a dedicated device called a router . Routing is a key feature of the Internet because it enables messages to pass from one computer to another and eventually reach the target machine. Each intermediary computer performs routing by passing along the message to the next computer. Part of this process involves analyzing a routing table to determine the best path. Routing is often confused with bridging, which performs a similar function. The principal difference between the two is that bridging occurs at a lower level and is therefore more of a hardware function whereas routing occurs at a higher level where the software component is more important. And because routing occurs at a higher level, it can perform more complex analysis to determine the optimal path for the packet. A routing protocol sends and receives routing information packets to and from other routers. A routed protocol can be routed by a router, which means that it can be forwarded from one router to another. Yes, there are protocols that can't be routed, such as NetBEUI (Network Basic Input Output System Extended User Interface). That a routed protocol can be routed may seem obvious, but unless you know how to differentiate it from a routing protocol, you may have trouble with the wording for some questions on the exam. A protocol is a set of rules that defines how two devices communicate with one another. It also defines the format for the packets used to transmit data over communications lines. A routed protocol contains the data elements required for a packet to be sent outside its host network or network segment. In other words, a routed protocol can be routed. Protocols used to communicate routing information between routers within an autonomous system are Interior Gateway Protocols (IGP), which are routing protocols, but not routed protocols. Routing protocols gather and share the routing information used to maintain and update routing tables. That routing information is in turn used to route a routed protocol to its final destination. Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP) are the routing protocols you need to know for the exam. If you can remember what the abbreviations mean, you'll remember that they are routing protocols because they have routing in their names. Remember, too, that they are not routed protocols. In short, routed protocols route your data and routing protocols send routing updates between routers about the status of the network so that your routed protocol data can be routed. Got that? No? Well, try this to help keep it straight:
  • Purpose: This figure introduces students to routing. The router must accomplish the items listed in the figure for routing to occur. Emphasize: Path determination occurs at Layer 3, the network layer. The path determination function enables a router to evaluate the available paths to a destination and to establish the best path. Routing services use network topology information when evaluating network paths. This information can be configured by the network administrator (static routes) or collected through dynamic processes (routing protocols) running in the network. Transition: How do you represent the path to the packet’s destination?
  • Purpose: This figure explains that routers must learn about paths not directly connected. Emphasize: The router already knows about directly connected networks. It must learn about those networks not connected. This chapter describes how routers learn about those paths.
  • 1. Internet Control Message Protocol (ICMP) creates an echo request payload (which is just the alphabet in the data field). 2. ICMP hands that payload to Internet Protocol (IP), which then creates a packet. 3. Once the packet is created, IP determines whether the destination IP address is on the local network or a remote one. 4. Since IP determines that this is a remote request, the packet needs to be sent to the default gateway so the packet can be routed to the remote network. The Registry in Windows is parsed to find the configured default gateway. 5. The default gateway of host 172.16.10.2 (Host_A) is configured to 172.16.10.1. To be able to send this packet to the default gateway, the hardware address of the router’s interface Ethernet 0 (configured with the IP address of 172.16.10.1) must be known. 6. Next, the ARP cache is checked to see if the IP address of the default gateway has already been resolved to a hardware address: If the hardware address isn’t already in the ARP cache of the host, an ARP broadcast is sent out onto the local network to search for the hardware address of 172.16.10.1. The router responds to the request and provides the hardware address of Ethernet 0, and the host caches this address. The router also caches the hardware address of Host_A in its ARP cache. 7. Once the packet and destination hardware address are handed to the Data Link layer, the LAN driver is used to provide media access via the type of LAN being used (in this example, Ethernet). A frame is then generated, encapsulating the packet with control information. Within that frame are the hardware destination and source addresses, plus, in this case, an Ether-Type field that describes the Network layer protocol that handed the packet to the Data Link layer—in this instance, IP. At the end of the frame is something called a Frame Check Sequence (FCS) field that houses the result of the cyclic redundancy check (CRC). 8. Once the frame is completed, it’s handed down to the Physical layer to be put on the physical medium (in this example, twisted-pair wire) one bit at a time. 9. Every device in the collision domain receives these bits and builds the frame. They each run a CRC and check the answer in the FCS field. If the answers don’t match, the frame is discarded. _ If the CRC matches, then the hardware destination address is checked to see if it matches, too (which, in this example, is the router’s interface Ethernet 0). If it’s a match, then the Ether-Type field is checked to find the protocol used at the Network layer. 10. The packet is pulled from the frame, and what is left of the frame is discarded. The packet is handed to the protocol listed in the Ether-Type field—it’s given to IP. 11. IP receives the packet and checks the IP destination address. Since the packet’s destination address doesn’t match any of the addresses configured on the receiving router itself, the router will look up the destination IP network address in its routing table. 12. The routing table must have an entry for the network 172.16.20.0, or the packet will be discarded Immediately and an ICMP message will be sent back to the originating device with a “destination network unreachable” message. 13. If the router does find an entry for the destination network in its table, the packet is switched to the exit interface—in this example, interface Ethernet 1. 14. The router packet-switches the packet to the Ethernet 1 buffer. 15. The Ethernet 1 buffer needs to know the hardware address of the destination host and first checks the ARP cache. If the hardware address of Host_B has already been resolved, then the packet and the hardware address are handed down to the Data Link layer to be framed. If the hardware address has not already been resolved, the router sends an ARP request out E1 looking for the hardware address of 172.16.20.2. Host_B responds with its hardware address, and the packet and destination hardware address are both sent to the Data Link layer for framing. 16. The Data Link layer creates a frame with the destination and source hardware address, Ether-Type field, and FCS field at the end of the frame. The frame is handed to the Physical layer to be sent out on the physical medium one bit at a time. 17. Host_B receives the frame and immediately runs a CRC. If the result matches what’s in the FCS field, the hardware destination address is then checked. If the host finds a match, the Ether-Type field is then checked to determine the protocol that the packet should be handed to at the Network layer—IP, in this example. 18. At the Network layer, IP receives the packet and checks the IP destination address. Since there’s finally a match made, the protocol field is checked to find out whom the payload should be given to. 19. The payload is handed to ICMP, which understands that this is an echo request. ICMP responds to this by immediately discarding the packet and generating a new payload as an echo reply. 20. A packet is then created including the source and destination address, protocol field, and payload. The destination device is now Host_A. 21. IP then checks to see whether the destination IP address is a device on the local LAN or on a remote network. Since the destination device is on a remote network, the packet needs to be sent to the default gateway. 22. The default gateway IP address is found in the Registry of the Windows device, and the ARP cache is checked to see if the hardware address has already been resolved from an IP address. 23. Once the hardware address of the default gateway is found, the packet and destination hardware addresses are handed down to the Data Link layer for framing. 24. The Data Link layer frames the packet of information and includes the following in the header: _ The destination and source hardware address _ The Ether-Type field with 0x0800 (IP) in it _ The FCS field with the CRC result in tow 25. The frame is now handed down to the Physical layer to be sent out over the network medium one bit at a time. 26. The router’s Ethernet 1 interface receives the bits and builds a frame. The CRC is run, and the FCS field is checked to make sure the answers match. 27. Once the CRC is found to be okay, the hardware destination address is checked. Since the router’s interface is a match, the packet is pulled from the frame and the Ether-Type field is checked to see what protocol at the Network layer the packet should be delivered to. 28. The protocol is determined to be IP, so it gets the packet. IP runs a CRC check on the IP header first, and then checks the destination IP address. 29. But the router does know how to get to network 172.16.10.0—the exit interface is Ethernet 0—so the packet is switched to interface Ethernet 0. 30. The router checks the ARP cache to determine whether the hardware address for 172.16.10.2 has already been resolved. 31. Since the hardware address to 172.16.10.2 is already cached from the originating trip to Host_B, the hardware address and packet are handed to the Data Link layer. 32. The Data Link layer builds a frame with the destination hardware address and source hardware address, and then puts IP in the Ether-Type field. A CRC is run on the frame, and the result is placed in the FCS field. 33. The frame is then handed to the Physical layer to be sent out onto the local network one bit at a time. 34. The destination host receives the frame, runs a CRC, checks the destination hardware address, and looks in the Ether-Type field to find out whom to hand the packet to. 35. IP is the designated receiver, and after the packet is handed to IP at the Network layer, it checks the protocol field for further direction. IP finds instructions to give the payload to ICMP, and ICMP determines the packet to be an ICMP echo reply. 36. ICMP acknowledges that it has received the reply by sending an exclamation point (!) to the user interface. ICMP then attempts to send four more echo requests to the destination host.
  • The router Serial to serial AUI to Host Change Host name to R1 AND r2
  • The router Serial to serial AUI to Host Change Host name to R1 AND R2
  • Purpose: This figure describes the command syntax used to establish an IP static route. Emphasize: A static route allows manual configuration of the routing table. No dynamic changes to this table entry will occur as long as the path is active. Routing updates are not sent on a link that is only defined by a static route; hence, conserving bandwidth. The ip route field descriptions are as follows: network —Destination network or subnet mask —Subnet mask address —IP address of next-hop router interface —Name of the interface to use to get to the destination network Transition: The next figure provides a static route configuration example.
  • Purpose: This figure describes the command syntax used to establish an IP static route. Emphasize: A static route allows manual configuration of the routing table. No dynamic changes to this table entry will occur as long as the path is active. Routing updates are not sent on a link that is only defined by a static route; hence, conserving bandwidth. Describe the The ip route field descriptions: network—destination network or subnet mask—subnet mask address—IP address of next hop router interface—name of interface to use to get to destination network. Transition: The next figure provides a static route configuration example.
  • The router Serial to serial AUI to Host Change Host name to R1 AND R2
  • The router Serial to serial AUI to Host Change Host name to R1 AND R2
  • Purpose: This figure gives an example of a default route configuration. Emphasize: With an address and subnet mask of 0.0.0.0 0.0.0.0 in the ip route statement, packets for any network not listed in the routing table will be sent to the next hop, 172.16.2.2.
  • The router Serial to serial AUI to Host Change Host name to R1 AND r2
  • Purpose: This figure introduces students to routing protocols and compares routing protocols to routed protocols. Emphasize: If network 10.120.2.0 wants to know about network 172.16.2.0, it must learn it from its S0 (or possibly S1) interface. If you have100’s of routers it become difficult to configure static routes Static has less overhead,
  • Purpose: This figure discusses autonomous systems, IGPs and EGPs. Emphasize: Introduce the interior/exterior distinctions for routing protocols, as follows: Interior routing protocols are used within a single autonomous system Exterior routing protocols are used to communicate between autonomous systems The design criteria for an interior routing protocol require it to find the best path through the network. In other words, the metric and how that metric is used is the most important element in an interior routing protocol. Exterior protocols are used to exchange routing information between networks that do not share a common administration. IP exterior gateway protocols require the following three sets of information before routing can begin: A list of neighbor (or peer) routers or access servers with which to exchange routing information A list of networks to advertise as directly reachable The autonomous system number of the local router
  • Purpose: This figure introduces the three classes of routing protocols. Emphasize: There is no single best routing protocol. Note: Distance vector routing protocol operation is covered in detail later in this course. Link state and hybrid are only briefly explained after the distance vector discussion. Refer students to the ACRC to learn more about link-state and hybrid routing protocols.
  • Distance vector algorithms do not allow a router to know the exact topology of an internetwork. This information is somewhat same to the information found on signs at a highway intersection. A sign points toward a road leading away from the intersection and indicates the distance to the destination. Further down the highway, another sign also points toward the destination, but now the distance to the destination is shorter. Distance is interm of HOPS Vector is direction Exchange entire routing tables with all neighbors at regular intervals More BW consumed This is also know as routing by rumor
  • Basis for All other routing protocol Algorithm Think that you are going for a trip from Mumbai to Delhi, there are two paths one 1500 Kms and another 1200Kms The routing table contains information about two routes But there is a piece of information which tells one route is better than other, that is known as Metric
  • RIP uses Hop count as metric, IGRP uses Composite Metric The composite Metric are bandwidth, Delay, Load, Reliability and MTU
  • When Network 5 fails, Router E tells Router C. This causes Router C to stop routing to Network5 through Router E. But Routers A, B, and D don’t know about Network 5 yet, so they keep sending out update information. Router C will eventually send out its update and cause B to stop routing to Network 5, but Routers A and D are still not updated. To them, it appears that Network 5 is still available through Router B with a metric of 3. The problem occurs when Router A sends out its regular 30-second “Hello, I’m still here these are the links I know about” message, which includes the ability to reach Network 5 and now Routers B and D receive the wonderful news that Network 5 can be reached from Router A, so Routers B and D then send out the information that Network 5 is available. Any packet destined for Network 5 will go to Router A, to Router B, and then back to Router A. This is a routing loop
  • Layer 3 of 3 Emphasize: Layer 3 adds the final entries received some time later that have distances of 2 from routers A and C.
  • Slide 1 of 4 Purpose: This figure describes the first of the general problems that a distance vector protocol could face without the corrective influence of some countermeasure. Emphasize: Layer 1 shows the original state of the network and routing tables. All routers have consistent knowledge and correct routing tables. In this example, the cost function is hop count, so the cost of each link is 1. Router C is directly connected to network 10.4.0.0 with a distance of 0. Router A’s path to network 10.4.0.0 is through router B, with a hop count of 2.
  • Slide 2 of 4 Emphasize: In Layer 2, router C has detected the failure of network 10.4.0.0 and stops routing packets out its E0 interface. However, router A has not yet received notification of the failure and still believes it can access network 10.4.0.0 through router B. Router A’s routing table still reflects a path to network 10.4.0.0 with a distance of 2.
  • Slide 3 of 4 Emphasize: Because router B’s routing table indicates a path to network 10.4.0.0, router C believes it now has a viable path to 10.4.0.0 through router B. Router C updates its routing table to reflect a path to network 10.4.0.0 with a hop count of 2.
  • Slide 4 of 4 Emphasize: In Layer 4, router A receives the new routing table from router B, detects the modified distance vector to network 10.4.0.0, and recalculates its own distance vector to network 10.4.0.0 as 3. If all routers in an internetwork do not have up-to-date, accurate information about the state of the internetwork, they might use incorrect routing information to make a routing decision. The use of incorrect information might cause packets to take less-than-optimum paths or paths that return packets to routers that they have already visited.
  • Purpose: This figure describes another of the general problems that a distance vector protocol could face without the corrective influence of some countermeasure. Emphasize: Both routers conclude that the best path to network 10.4.0.0 is through each other and continue to bounce packets destined for network 10.4.0.0 between each other, incrementing the distance vector by 1 each time. This condition, called count to infinity, continuously loops packets around the network, despite the fundamental fact that the destination network 10.4.0.0 is down. While the routers are counting to infinity, the invalid information allows a routing loop to exist. A related concept is the Time-to-Live (TTL) parameter. The TTL is a packet parameter that decreases each time a router processes the packet. When the TTL reaches zero, a router discards or drops the packet without forwarding it. A packet caught in a routing loop is removed from the internetwork when its TTL expires.
  • Slide 4 of 4 Emphasize: In Layer 4, router A receives the new routing table from router B, detects the modified distance vector to network 10.4.0.0, and recalculates its own distance vector to network 10.4.0.0 as 3. If all routers in an internetwork do not have up-to-date, accurate information about the state of the internetwork, they might use incorrect routing information to make a routing decision. The use of incorrect information might cause packets to take less-than-optimum paths or paths that return packets to routers that they have already visited.
  • Purpose: This figure describes a corrective measure that attempts to solve the routing loop problems that a distance vector protocol could face. Emphasize: Routing loops occur only when routing knowledge being propagated has not yet reached the entire internetwork—when the internetwork has not converged after a change. Fast convergence minimizes the chance for a routing loop to occur, but even the smallest interval leaves the possibility open. To avoid prolonging the count-to-infinity time span, distance vector protocols define infinity as some maximum number. This number refers to a routing metric, such as a hop count. With this approach, the routing protocol permits the routing loop until the metric exceeds its maximum allowed value. This example shows this defined maximum as 16 hops. Once the metric value exceeds the maximum, network 10.4.0.0 is considered unreachable.
  • Purpose: This figure introduces the corrective measure known as “split horizon.” The split horizon technique attempts to solve routing loops. Emphasize: The split horizon technique attempts to eliminate routing loops and speed up convergence. The rule of split horizon is that it is never useful to send information about a route back in the direction from which the original packet came. In the example: Router C originally announced a route to network 10.4.0.0 to router B. It makes no sense for router B to announce to router C that router B has access to network 10.4.0.0 through router C. Given that router B passed the announcement of its route to network 10.4.0.0 to router A, it makes no sense for router A to announce its distance from network 10.4.0.0 to router B. Because router B has no alternative path to network 10.4.0.0, router B concludes that network 10.4.0.0 is inaccessible. In its basic form, the split-horizon technique simply omits from the message any information about destinations routed on the link. This strategy relies either on routes never being announced or on old announcements fading away through a timeout mechanism. Split horizon also improves performance by eliminating unnecessary routing updates. Under normal circumstances, sending routing information back to the source of the information is unnecessary. * Splithorizon - the routing protocol advertises routes out an interface only if they were not learned from updates entering that interface.
  • Split Horizon. In looking at the routing loop example, you should have noticed that Router A ultimately let Router B know about a route to network 172.16.0.0, even though it originally learned that route from Router B. Split horizon is a rule that specifies that a router can never send information about a route back to the router that originally supplied the information. Had split horizon been used in our example, Router A would not have included information about network 172.16.0.0 in its update to Router B.
  • Triggered Updates. Obviously the interval between routing table updates is part of the problem that leads to routing loops. Instead of relying on regular periodic updates, distance vector protocols will send out a triggered update when a metric to reach a network increases. In our example, Router C would immediately send out an update about network 172.16.0.0 not being available to Router B, who would then immediately send out an update to Router A. While triggered updates cause a little more network traffic in the short term, they go a long way towards faster convergence on a distance-vector network
  • When a router receives an update from a neighbor indicating that a previously accessible network isn’t working and is inaccessible, the holddown timer will start. If a new update arrives from a neighbor with a better metric than the original network entry, the holddown is removed and data is passed. But if an update is received from a neighbor router before the holddown timer expires and it has an equal or lower metric than the previous route, the update is ignored and the holddown timer keeps ticking. This allows more time for the network to stabilize before trying to converge
  • RIP versions 1 and 2 also use the concept of hold timers. When a destination has become unreachable (or the metric has increased enough to cause poisoning), the destination goes into "holddown". During this state, no new path will be accepted for the same destination for this amount of time. The hold time indicates how long this state should last. * Hold-down timer - After finding out that a router to a subnet has failed, a router waits a certain period of time before believing any other routing information about that subnet.
  • RIP uses only hop count to determine the best path to a network. If RIP finds more than one link to the same remote network with the same hop count, it will automatically perform a round-robin load balancing. RIP can perform load balancing for up to six equal-cost links (four by default). However, a problem with this type of routing metric arises when the two links to a remote network are different bandwidths but the same hop count. Figure 5.9, for example, shows two links to remote network 172.16.10.0. Since network 172.16.30.0 is a T1 link with a bandwidth of 1.544Mbps, and network 172.16.20.0 is a 56K link, you’d want the router to choose the T1 over the 56K link, right? But because hop count is the only metric used with RIP routing, the two links would be seen as being of equal cost. This little snag is called pinhole congestion .
  • The router Serial to serial AUI to Host Change Host name to R1 AND r2
  • Purpose : This figure displays the show ip route command, which displays the contents of the router’s IP routing table. Emphasize : Discuss the IP routing table in detail. Show the locations of the hop count (metric) and the administrative distance (120). Discuss the following fields: R—Refers to routes learned from RIP. via—Refers to the router that informed us about this route. 00:00:07 timer value—RIP updates are every 30 seconds. Ask, “How long until the next update?” The interfaces used for the best path
  • Purpose : This figure shows the debug ip rip command. Emphasize : Explain that debug commands also provide information for monitoring IP. The first highlighted line lists the source of the updates. The router returned information about two destinations. The last highlighted line shows the broadcast address to which the router sent updates.
  • 152-5
  • Purpose: This chapter introduces the Cisco IOS™ CLI on the Catalyst® 1900 switch and router. Timing: This chapter should take about 2 hours to present. Note: The Catalyst 1900 switch only has a subset of the router Cisco IOS commands available. Contents: Introduction to Cisco IOS. Explain to the student what is IOS? Cisco Device startup procedures in general. IOS configuration source. General introduction to the IOS CLI . Cat 1900 switch startup procedures. Intro to Cat 1900 CLI. This part covers the basic configuration on the switch, like setting the IP address and hostname. More details about the various Cat 1900 switch configuration commands are explained in Chapter 6 and 7. Router startup procedures. More details on the router startup process is discussed in chapter 5. Router IOS CLI.
  • Purpose : The figure introduces the IGRP routing protocol. IGRP is a sophisticated distance vector routing protocol. Emphasize: The Interior Gateway Routing Protocol (IGRP) is a dynamic distance-vector routing protocol designed by Cisco in the mid-1980s for routing in an autonomous system that contains large, arbitrarily complex networks with diverse bandwidth and delay characteristics. Historically, IGRP became one of the success factors for the early Cisco IOS software capabilities because of its superiority to RIP version 1. The important IGRP characteristics are as follows: More scalability than RIP Fast response to network changes Sophisticated metric Multiple-path support
  • Purpose : This figure presents the IGRP metric with its five possible components. Emphasize : Bandwidth and delay are the two metrics that are most commonly used. They also comprise the default metric. Note : Changing IGRP metrics can have great impact on network performance. Describe the IGRP 24-bit metric field, as follows: Bandwidth—Minimum bandwidth on the route, in kilobits per second. Delay—Route delay, in tens of microseconds. Reliability—Likelihood of successful packet transmission, expressed as an integer from 0 to 255. Loading—Effective bandwidth of path. MTU—Minimum MTU in path, expressed in bytes. The following equation calculates the metric. It is presented for instructors and is not required to be taught: metric = [k1 x bandwidth + (k2 x bandwidth) / (256 - load) + k3 x delay] If k5 does not equal 0, an additional operation is done: metric = metric x (k5/(reliability + k4)) The default constant values are k1 = k3 = 1 and k2 = k4 = k5 = 0. Again, if default values are set, metric = bandwidth + delay. The constants (k1, k2, k3) can be changed using the metric weights command. Changes to the IGRP constant values should be made with great care.
  • Can explain pin hole congestion how RIP and IGRP Handles (Load Balancing) IGRP – Hop count 25, default - 100
  • The router Serial to serial AUI to Host Change Host name to R1 AND r2

C C N A  Day2 C C N A Day2 Presentation Transcript

  • Routers & Cisco IOS
  • Cisco IOS Cisco technology is built around the Cisco Internetwork Operating System (IOS), which is the software that controls the routing and switching functions of internetworking devices. A solid understanding of the IOS is essential for a network administrator.
  • The Purpose of Cisco IOS As with a computer, a router or switch cannot function without an operating system. Cisco calls its operating system the Cisco Internetwork Operating System or Cisco IOS.
  • Introduction to Routers A router is a special type of computer. It has the same basic components as a standard desktop PC. However, routers are designed to perform some very specific functions. Just as computers need operating systems to run software applications, routers need the Internetwork Operating System software (IOS) to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. The many parts of a router are shown below:
  • Router Memory Components ROM - Read Only Memory – Bootstrap/POST FLASH Memory - IOS Images are kept here - Erasable reprogrammable ROM - Contents are kept on Power down or reload RAM - Random Access memory - Routing Tables - Running Configuration - Contents are lost on reboot NVRAM - Start up configuration - Configuration Register - Contents are kept on reload
  • ROM
    • Read-Only Memory
    • ROM has the following characteristics and functions:
    • Maintains instructions for power-on self test (POST) diagnostics
    • Stores bootstrap program and basic operating system software
    • Mini IOS
  • RAM
    • Random Access Memory, also called dynamic RAM (DRAM)
    • RAM has the following characteristics and functions:
    • Stores routing tables
    • Holds ARP cache
    • Performs packet buffering (shared RAM)
    • Provides temporary memory for the configuration file of the router while the router is powered on
    • Loses content when router is powered down or restarted
  • NVRAM
    • Non-Volatile RAM
    • NVRAM has the following characteristics and functions:
    • Provides storage for the startup configuration file
    • Retains content when router is powered down or restarted
    • Configuration Register – 16 bit register which decides boot sequence
  • Flash
    • Flash memory has the following characteristics and functions:
    • Holds the operating system image (IOS)
    • Allows software to be updated without removing and replacing chips on the processor
    • Retains content when router is powered down or restarted
    • Can store multiple versions of IOS software
    • Is a type of electronically erasable, programmable ROM (EEPROM)
  • Interfaces
    • Interfaces have the following characteristics and functions:
    • Connect router to network for frame entry and exit
    • Can be on the motherboard or on a separate module
    • Types of interfaces:
    • Ethernet
    • Fast Ethernet
    • Serial
    • ISDN BRI
    • Loopback
    • Console
    • Aux
  • Router Internal Components
  • Router Power-On/Bootup Sequence
    • Perform power-on self test (POST).
    • Load and run bootstrap code.
    • Find the Cisco IOS software.
    • Load the Cisco IOS software.
    • Find the configuration.
    • Load the configuration.
    • Run the configured Cisco IOS software.
  • Boot Sequence ON OFF POST Bootstrap ROMMonitor RXBoot FLASH CR Configuration Register LOAD IOS C-File NVRAM Y N Running Setup Mode Checks All interfaces RAM 0 0 0 0 0 0 0 1 0 0 1 0 ROMMonitor RxBoot Flash 1 1 1 1 0 1 2-15 14 15 13 12 10 11 9 8 6 7 5 4 2 3 1 0 4 8 2 1 4 8 2 1 4 8 2 1 4 8 2 1
  • After the Post… After the POST, the following events occur as the router initializes: Step 1 The generic bootstrap loader in ROM executes. A bootstrap is a simple set of instructions that tests hardware and initializes the IOS for operation.  Step 2 The IOS can be found in several places. The boot field of the configuration register determines the location to be used in loading the IOS. Step 3 The operating system image is loaded. Step 4 The configuration file saved in NVRAM is loaded into main memory and executed one line at a time. The configuration commands start routing processes, supply addresses for interfaces, and define other operating characteristics of the router. Step 5 If no valid configuration file exists in NVRAM, the operating system searches for an available TFTP server. If no TFTP server is found, the setup dialog is initiated.  
  • Loading the Cisco IOS Software From Flash Memory
    • The flash memory file is decompressed into RAM.
  • Loading the Configuration
      • Load and execute the configuration from NVRAM.
      • If no configuration is present in NVRAM, enter setup mode.
  • External Components of a 2600 Router
  • Internal Components of a 2600 Router
  • Computer/Terminal Console Connection
  • Modem Connection to Console/Aux Port
  • HyperTerminal Session Properties
  • Establishing a HyperTerminal Session Take the following steps to connect a terminal to the console port on the router: First, connect the terminal using the RJ-45 to RJ-45 rollover cable and an RJ-45 to DB-9 or RJ-45 to DB-25 adapter. Then, configure the terminal or PC terminal emulation software for 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow control.
  • Router Command Line Interface
  • IOS File System Overview
  • Router LED Indicators Cisco routers use LED indicators to provide status information. Depending upon the Cisco router model, the LED indicators will vary. An interface LED indicates the activity of the corresponding interface. If an LED is off when the interface is active and the interface is correctly connected, a problem may be indicated. If an interface is extremely busy, its LED will always be on. The green OK LED to the right of the AUX port will be on after the system initializes correctly.
  • Router Configuration
  • Router User Interface Modes The Cisco command-line interface (CLI) uses a hierarchical structure. This structure requires entry into different modes to accomplish particular tasks. Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode. As a security feature the Cisco IOS software separates sessions into two access levels, user EXEC mode and privileged EXEC mode. The privileged EXEC mode is also known as enable mode .
  • Overview of Router Modes
  • Router Modes
  • CLI Command Modes All command-line interface (CLI) configuration changes to a Cisco router are made from the global configuration mode. Other more specific modes are entered depending upon the configuration change that is required. Global configuration mode commands are used in a router to apply configuration statements that affect the system as a whole. The following command moves the router into global configuration mode Router# configure terminal (or config t) Router(config)# When specific configuration modes are entered, the router prompt changes to indicate the current configuration mode. Typing exit from one of these specific configuration modes will return the router to global configuration mode. Pressing Ctrl-Z returns the router to all the way back privileged EXEC mode.
  • Show Version Command wg_ro_a# show version Cisco Internetwork Operating System Software IOS (tm) 2500 Software (C2500-JS-L), Version 12.0(3), RELEASE SOFTWARE (fc1) Copyright (c) 1986-1999 by cisco Systems, Inc. Compiled Mon 08-Feb-99 18:18 by phanguye Image text-base: 0x03050C84, data-base: 0x00001000 ROM: System Bootstrap, Version 11.0(10c), SOFTWARE BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c), RELEASE SOFTWARE(fc1) wg_ro_a uptime is 20 minutes System restarted by reload System image file is "flash:c2500-js-l_120-3.bin" (output omitted) --More-- Configuration register is 0x2102
  • Viewing the Configuration
  • show running-config and show startup-config Commands wg_ro_c# show startup-config Using 1359 out of 32762 bytes ! version 12.0 ! -- More -- wg_ro_c # show running-config Building configuration... Current configuration: ! version 12.0 ! -- More -- In NVRAM In RAM
      • Displays the current and saved configuration
    • Configurations in two locations - RAM and NVRAM.
    • The running configuration is stored in RAM.
    • Any configuration changes to the router are made to the running-configuration and take effect immediately after the command is entered.
    • The startup-configuration is saved in NVRAM and is loaded into the router's running-configuration when the router boots up.
    • To save the running-configuration to the startup configuration, type the following from privileged EXEC mode (i.e. at the "Router#" prompt.)
      • Router# copy run start
    Saving Configurations
  • Command Abbreviation
    • Show Configuration – sh conf
    • Configure Terminal – conf t
    • Line auxillary – line aux
    • Line console – line con
  • Configuring a Router’s Name A router should be given a unique name as one of the first configuration tasks. This task is accomplished in global configuration mode using the following commands: Router(config)#hostname Gates Gates(config)# As soon as the Enter key is pressed, the prompt changes from the default host name (Router) to the newly configured host name (which is Gates in the example above).
  • Setting the Clock with Help
  • Message Of The Day (MOTD) A message-of-the-day (MOTD) banner can be displayed on all connected terminals. Enter global configuration mode by using the command config t Enter the command banner motd # Welcome to Gates Training # . Save changes by issuing the command copy run start
  • Privileged Mode Command
    • # show startup-config
    • # show running-config
    • # show version
    • # show flash
    • # show interfaces
    • # show interfaces s 0
    • # show history
    • # show terminal
    • # terminal history size 25
  • Password
    • Passwords restrict access to routers.
    • Passwords should always be configured for virtual terminal lines and the console line.
    • Passwords are also used to control access to privileged EXEC mode so that only authorized users may make changes to the configuration file.
  • Passwords
    • There are five passwords for Router
      • Privileged Mode Password – 2
      • Line Console Password
      • Auxiliary Port Password
      • Telnet Password
  • Privileged Mode Password
    • Gates(config)# enable password gates
    • Encrypted privilege mode password
    • Gates(config)# enable secret gates1
  • Line Password
    • Gates(config)# line console 0
    • Gates(config)# password cisco
    • Gates(config)# login
  • Aux Port Password
    • Gates(config)# line aux 0
    • Gates(config)# password cisco
    • Gates(config)# login
  • Connecting to Aux Port
  • Configuring a Telnet Password
    • A password must be set on one or more of the virtual terminal (VTY) lines for users to gain remote access to the router using Telnet.
    • Typically Cisco routers support five VTY lines numbered 0 through 4.
  • Telnet Password
    • Gates(config)# line vty 0 4
    • Gates(config)# password cisco
    • Gates(config)# login
  • Encrypting Passwords
    • Only the enable secret password is encrypted by default
    • Need to manually configure the user-mode and enable passwords for encryption
    • To manually encrypt your passwords, use the service password-encryption command
    • Router#config t
    • Enter configuration commands, one per line. End with CNTL/Z.
    • Router(config)#service password-encryption
  • Disable Passwords
    • Gates(config)# no enable password
    • Gates(config)# no enable secret
    • For the Console
    • Gates(config)# line con 0
    • Gates(config)# no password
    • Gates(config)# line vty 0 4
    • Gates(config)# no password
  • LAB – Interface Configuration S0 S0 R1 R2 E0 10.0.0.1 10.0.0.2 30.0.0.2 20.0.0.1 20.0.0.2 30.0.0.1 A S0 E0 40.0.0.2 40.0.0.1 B S1 R3
  • Descriptions
    • Setting descriptions on an interface is helpful to the administrator
    • Only locally significant
    • R1(config)# int e0
      • R1(config-if)# description Sales Lan
      • R1(config-if)# int s0
      • R1(config-if)# desc Wan to Mumbai
  • Configuring Interfaces
    • An interface needs an IP Address and a Subnet Mask to be configured.
    • All interfaces are “shutdown” by default.
    • The DCE end of a serial interface needs a clock rate.
    • R1# config t R1(config)# int e0
    • R1(config)# Description Connoted to Host R1(config-if)# ip address 10.0.0.1 255.0.0.0
    • R1(config-if)# no shutdown
    • R1(config-if)# exit
    • R1(config)# interface serial 0
    • R1(config-if)# ip address 20.0.0.1 255.255.255.0
    • R1(config-if)# bandwidth 64
    • R1(config-if)# clock rate 64000 (required for serial DCE only) R1(config-if)# no shutdown
    • R1(config-if)# exit
    • R1(config)# exit
    • R1#
    • On new routers, Serial 1 would be just Serial 0/ 1 and e0 would be f0/0 .
    • s = serial e = Ethernet f = fast Ethernet
  • DCE DTE
    • To find out DCE or DTE
    • #Show controllers s 0
  • Viewing Configuration
    • To Check the status of interface
    • #Show IP interface brief
    • or
    • #Sh IP int brief
  • Saving and Erasing Configurations
    • To copy RAM to NVRAM
    • # copy run startup-config
    • To remove all configuration
    • # erase startup-config
    • # reload
  • Routing
  • Objectives
    • Upon completion of this chapter, you will be able to complete the following tasks:
      • Distinguish the use and operation of static and dynamic routes
      • Configure and verify a static route
      • Identify how distance vector IP routing protocols such as RIP and IGRP operate on Cisco routers
      • Enable Routing Information Protocol (RIP)
      • Enable Interior Gateway Routing Protocol (IGRP)
      • Verify IP routing with show and debug commands
  • Routing
      • The process of transferring data from one local area network to another
      • Layer 3 devices
      • Routed protocol Enables to forward packet from one router to another – Ex – IP, IPX
      • Routing protocol sends and receives routing information packets to and from other routers – Ex -RIP, OSPF , IGRP
      • Routing protocols gather and share the routing information used to maintain and update routing tables.
      • That routing information is in turn used to route a routed protocol to its final destination
  • Routing
    • From
      • Raj
      • House #213, 4 th Street
      • Jayanagar, Bangalore
    • To
      • Ram
      • House #452, 2 nd Street
      • Dadar, Mumbai
    • To route, a router needs to know:
      • Destination addresses
      • Sources it can learn from
      • Possible routes
      • Best route
    What is Routing? 172.16.1.0 10.120.2.0
  • What is Routing? (cont.) Network Protocol Destination Network Connected Learned 10.120.2.0 172.16.1.0 Exit Interface E0 S0 Routed Protocol: IP
      • Routers must learn destinations that are not directly connected
    172.16.1.0 10.120.2.0 E0 S0
  • Route Types
    • Static routing - network administrator configures information about remote networks manually. They are used to reduce overhead and for security.
    • Dynamic routing - information is learned from other routers, and routing protocols adjust routes automatically.
    • Because of the extra administrative requirements, static routing does not have the scalability of dynamic routing.
  • IP Routing Process
    • Step-by-step what happens when Host A wants to communicate with Host B on a different network
    • A user on Host A pings Host B’s IP address.
    R1 E0 E1 10.0.0.1 10.0.0.2 A B 20.0.0.2 20.0.0.1
  • LAB Configuration S0 S0 R1 R2 E0 E0 10.0.0.1 10.0.0.2 30.0.0.2 20.0.0.1 20.0.0.2 30.0.0.1 A B
  • LAB – Interface Configuration S0 S0 R1 R2 E0 10.0.0.1 10.0.0.2 30.0.0.2 20.0.0.1 20.0.0.2 30.0.0.1 A S0 E0 40.0.0.2 40.0.0.1 B S1 R3
  • Test The Connection
    • Host A can ping router R1 and R2
    • To enable Host A to Ping Host B we need to configure Routes
  • IP Routing
    • The different types of routing are:
      • Static routing
      • Default routing
      • Dynamic routing
  • Static Routes
    • Benefits
      • No overhead on the router CPU
      • No bandwidth usage between routers
      • Adds security
    • Disadvantage
      • Administrator must really understand the internetwork
      • If a network is added to the internetwork, the administrator has to add a route to it on all routers
      • Not feasible in large networks
      • R1(config)# iproute DestAddress SNM Nexthop address
    Static Route Configuration R1(config)#ip route network [ mask ] { address | interface }[ distance ] [permanent]
      • ip route The command used to create the static route.
      • destination_network The network you’re placing in the routing table.
      • mask The subnet mask being used on the network.
      • next-hop_address The address of the next-hop router that will receive the packet and forward it to the remote network. This is a router interface that’s on a directly connected network.
      • exitinterface You can use it in place of the next-hop address if you want, but it’s got to be on a point-to-point link, such as a WAN
      • administrative_distance By default, static routes have an administrative distance of 1 (or even 0 if you use an exit interface instead of a next-hop address)
      • permanent If the interface is shut down, or the router can’t communicate to the next-hop router, the route will automatically be discarded from the routing table. Choosing the permanent option keeps the entry in the routing table no matter what happens.
    Static Route Configuration ip route [ destination_network ] [ mask ] [ next-hop_address or exitinterface ] [ administrative_distance ] [permanent R1(config)#ip route 30.0.0.0 255.0.0.0 20.0.0.2
  • LAB – Static Route Configuration S0 S0 R1 R2 E0 10.0.0.1 10.0.0.2 30.0.0.2 20.0.0.1 20.0.0.2 30.0.0.1 A S0 E0 40.0.0.2 40.0.0.1 B S1 R3 R1# config t R1(config)#ip route 30.0.0.0 255.0.0.0 20.0.0.2 R1(config)#ip route 40.0.0.0 255.0.0.0 20.0.0.2 R2# config t R2(config)#ip route 10.0.0.0 255.0.0.0 20.0.0.1 R2(config)#ip route 40.0.0.0 255.0.0.0 30.0.0.2 R3# config t R3(config)#ip route 10.0.0.0 255.0.0.0 30.0.0.1 R3(config)#ip route 20.0.0.0 255.0.0.0 30.0.0.1
  • Verifying Static Route Configuration
    • After static routes are configured it is important to verify that they are present in the routing table and that routing is working as expected.
    • The command show running-config is used to view the active configuration in RAM to verify that the static route was entered correctly.
    • The show ip route command is used to make sure that the static route is present in the routing table.
  • Removing IP Route S0 S0 R1 R2 E0 10.0.0.1 10.0.0.2 30.0.0.2 20.0.0.1 20.0.0.2 30.0.0.1 A S0 E0 40.0.0.2 40.0.0.1 B S1 R3 R1# config t R1(config)#no ip route 30.0.0.0 255.0.0.0 20.0.0.2 R1(config)#no ip route 40.0.0.0 255.0.0.0 20.0.0.2 R2# config t R2(config)#no ip route 10.0.0.0 255.0.0.0 20.0.0.1 R2(config)#no ip route 40.0.0.0 255.0.0.0 30.0.0.2 R3# config t R3(config)#no ip route 10.0.0.0 255.0.0.0 30.0.0.1 R3(config)#no ip route 20.0.0.0 255.0.0.0 30.0.0.1
  • Default Routes
    • Can only use default routing on stub networks
    • Stub networks are those with only one exit path out of the network
    • The only routers that are considered to be in a stub network are R1 and R3
    S0 S0 R1 R2 E0 E0 10.0.0.1 10.0.0.2 40.0.0.2 20.0.0.1 20.0.0.2 30.0.0.1 S0 S1 30.0.0.2 40.0.0.1 R3 A B
  • Default Routes Stub Network ip route 0.0.0.0 0.0.0.0 172.16.2.2 172.16.2.1 SO 172.16.1.0 B 172.16.2.2 Network A B
      • This route allows the stub network to reach all known networks beyond router A.
    10.0.0.0
  • Configuring Default Routes Default routes are used to route packets with destinations that do not match any of the other routes in the routing table. A default route is actually a special static route that uses this format: ip route 0.0.0.0 0.0.0.0 [ next-hop-address | outgoing interface ] This is sometimes referred to as a “Quad-Zero” route. Example using next hop address: Router(config)# ip route 0.0.0.0 0.0.0.0 172.16.4.1 Example using the exit interface: Router(config)# ip route 0.0.0.0 0.0.0.0 s0/0
  • LAB Configuration S0 S0 R1 R2 E0 E0 10.0.0.1 10.0.0.2 40.0.0.2 20.0.0.1 20.0.0.2 30.0.0.1 S0 S1 30.0.0.2 40.0.0.1 R3 A B
  • Default Route LAB Configuration S0 S0 R1 R2 E0 E0 10.0.0.1 10.0.0.2 40.0.0.2 20.0.0.1 20.0.0.2 30.0.0.1 S0 S1 30.0.0.2 40.0.0.1 R3 R1# config t R1(config)#ip route 0.0.0.0 0.0.0.0 20.0.0.2 R3# config t R3(config)#ip route 0.0.0.0 0.0.0.0 30.0.0.1 R2# config t R2(config)#ip route 10.0.0.0 255.0.0.0 20.0.0.1 R2(config)#ip route 40.0.0.0 255.0.0.0 30.0.0.2 A B
  • What is a Routing Protocol?
    • Routing protocols are used between routers to determine paths and maintain routing tables.
    • Once the path is determined a router can route a routed protocol.
    Network Protocol Destination Network Connected RIP IGRP 10.120.2.0 172.16.2.0 172.17.3.0 Exit Interface E0 S0 S1 Routed Protocol: IP Routing protocol: RIP, IGRP 172.17.3.0 172.16.1.0 10.120.2.0 E0 S0
  • Autonomous System AS 2000 AS 3000 AS 1000
    • An Autonomous System (AS) is a group of IP networks, which has a single and clearly defined routing policy.
    • Group of routers which can exchange updates
    • AS are identified by numbers
    Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67) All Routing protocols are categorized as IGP or EGP Routing Categories IGP Interior Gateway Protocols are used for routing decisions within an Autonomous System. Exterior Gateway Protocols are used for routing between Autonomous Systems EGP
  • IGP Interior Gateway Protocol (IGP) Interior Gateway Protocol (IGP) AS 1000 AS 2000 AS 3000 Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67) Routing Categories Exterior Gateway Protocol (EGP) EGP EGP EGP
  • Autonomous Systems: Interior or Exterior Routing Protocols
      • An autonomous system is a collection of networks under a common administrative domain.
      • IGPs operate within an autonomous system.
      • EGPs connect different autonomous systems .
  • Types or Classes of Routing Protocols
    • Distance Vector
      • RIP V1
      • IGRP
      • RIP V2
    • Link state
      • OSPF
    • Hybrid
      • EIGRP
    Types or Classes of Routing Protocols
  • Classful Routing Overview
      • Classful routing protocols do not include the subnet mask with the route advertisement.
      • Within the same network, consistency of the subnet masks is assumed.
      • Summary routes are exchanged between foreign networks.
      • Examples of classful routing protocols:
        • RIP Version 1 (RIPv1)
        • IGRP
  • Classless Routing Overview
      • Classless routing protocols include the subnet mask with the route advertisement.
      • Classless routing protocols support variable-length subnet masking (VLSM) and subnetting
      • Examples of classless routing protocols:
        • RIP Version 2 (RIPv2)
        • EIGRP
        • OSPF
        • IS-IS
    • Routers pass periodic copies of routing table to neighbor routers and accumulate distance vectors.
    Distance Vector Routing Protocols
  • Distance Vector
    • Uses Bellman Ford Algorithm
    • It needs to find out the shortest path from one network to other
    • How to determine which path is best?
    192.168.10.1 192.168.20.1
  • Distance Vector
    • There are two Distance Vector Protocol, Both uses different metric
    • RIP – Hops
    • IGRP - Composite
    192.168.20.1 192.168.10.1
  • Distance Vector
    • DV protocol are known as Routing by rumor
    • RIP uses only Hop count
    • RI routing table metric for 192.168.20.1 network will be
      • 3
      • 2
    192.168.20.1 RIP 0 1 1 2 2 3 R1 192.168.10.1
  • Distance Vector
    • IGGRP uses bandwidth and delay as Metric
    • RI routing table metric for 192.168.20.1 network will be
      • 30
      • 60
    192.168.20.1 IGRP 56 kbps 1 Mbps 1 Mbps 1 Mbps 56 kbps R1 10 10 10 30 30 192.168.10.1 192.168.10.1
  • Routing Loops A network problem in which packets continue to be routed in an endless circle
    • Routers discover the best path to destinations from each neighbor.
    Sources of Information and Discovering Routes
    • Each node maintains the distance from itself to each possible destination network.
    Inconsistent Routing Entries
    • Slow convergence produces inconsistent routing.
    Inconsistent Routing Entries (Cont.)
  • Inconsistent Routing Entries (Cont.)
    • Router C concludes that the best path to network 10.4.0.0 is through router B.
  • Inconsistent Routing Entries (Cont.)
    • Router A updates its table to reflect the new but erroneous hop count.
    • Hop count for network 10.4.0.0 counts to infinity.
    Count to Infinity
  • Routing Loops
    • Packets for network 10.4.0.0 bounce (loop) between routers B and C.
    • Define a limit on the number of hops to prevent infinite loops.
    Defining a Maximum
  • Maximum Hop Count
    • One way of solving routing loop problem is to define a maximum hop count.
    • RIP permits a hop count of up to 15, so anything that requires 16 hops is deemed unreachable
    • The maximum hop count will control how long it takes for a routing table entry to become invalid
    • It is never useful to send information about a route back in the direction from which the original information came.
    Split Horizon
  • Split Horizon
    • Solution to the Routing Loop problem
    • Split Horizon is a rule that routing information cannot be sent back in the direction from which it was received
    • Had split horizon been used in our example, Router B would not have included information about network 10.4.0.0 in its update to Router C.
  • Route Poisoning
    • Route Poisoning. Usually used in conjunction with split horizon
    • Route poisoning involves explicitly poisoning a routing table entry for an unreachable network
    • Once Router C learned that network 10.4.0.0 was unavailable it would have immediately poisoned the route to that network by setting its hop count to the routing protocol’s infinity value
    • In the case of RIP, that would mean a hop count of 16 .
  • Triggered Updates
    • New routing tables are sent to neighboring routers on a regular basis.
    • RIP updates occur every 30 seconds
    • However a triggered update is sent immediately in response to some change in the routing table.
    • The router that detects a topology change immediately sends an update message to adjacent routers that, in turn, generate triggered updates notifying their adjacent neighbors of the change.
    • Triggered updates, used in conjunction with route poisoning, ensure that all routers know of failed routes.
  • Triggered Updates Graphic
  • Holddowns
    • Holddowns are a technique used to ensure that a route recently removed or changed is not reinstated by a routing table update from another route
    • Holddown prevents regular update messages from reinstating a route that is going up and down (called flapping)
    • Holddowns prevent routes from changing too rapidly by allowing time for either the downed route to come back up
    • Holddowns make a router wait a period of time before accepting an update for a network whose status or metric has recently changed
  • Solution: Holddown Timers
  • Pinhole Congestion 192.168.10.1 192.168.20.1 1Mbps 1Mbps 56kbps 56kbps
  • RIP Timers
    • Route update timer Sets the interval (typically 30 seconds) between periodic routing updates
    • Route invalid timer Determines the length of time (180 seconds) before a router determines that a route has become invalid
    • Holddown timer This sets the amount of time during which routing information is suppressed. This continues until either an update packet is received with a better metric or until the holddown timer expires. The default is 180 seconds
    • Route flush time r Sets the time between a route becoming invalid and its removal from the routing table (240 seconds).
  • Routing Information Protocol (RIP)
    • Routing Information Protocol (RIP) is a true distance-vector routing protocol.
    • It sends the complete routing table out to all active interfaces every 30 seconds
    • RIP only uses hop count to determine the best way to a remote network
    • It has a maximum allowable hop count of 15
    • AD is 120
    • Bellman-ford algorithm
    • Works well in small networks, but it’s inefficient on large networks
    • RIP version 1 uses only classful routing, which means that all devices in the network must use the same subnet mask
    • RIP version 2 does send subnet mask information with the route updates. This is called classless routing .
  • Router Configuration The router command starts a routing process. The network command is required because it enables the routing process to determine which interfaces participate in the sending and receiving of routing updates. An example of a routing configuration is: Gates(config)# router rip Gates(config-router)# network 172.16.0.0 The network numbers are based on the network class addresses, not subnet addresses or individual host addresses.
  • RIP Configuration S0 S0 R1 R2 E0 E0 192.168.10.1 S0 S1 R3 R1# config t R1(config)# )#router rip R1(config)#network 192.168.10.0 R1(config)#network 192.168.20.0 R2# config t R2(config)#router rip R2(config)#network 192.168.20.0 R2(config)#network 192.168.30.0 192.168.10.2 192.168.20.1 192.168.20.2 192.168.30.1 192.168.30.2 192.168.40.1 192.168.40.2 R3# config t R3(config)# )#router rip R3(config)#network 192.168.30.0 R3(config)#network 192.168.40.0 A B
  • Verifying RIP Configuration
  • Displaying the IP Routing Table
  • debug ip rip Command
  • Passive Interface
    • Passive-interface command prevents RIP update broadcasts from being sent out a defined interface, but same interface can still receive RIP updates
        • R1# config t
        • R1(config)# router rip
        • R1(config-router)# network 192.168.10.0
        • R1(config-router)# passive-interface serial 0
    • Passive-interface command depends upon the routing protocol
    • RIP router with a passive interface will still learn about the networks advertised by other routers
    • EIGRP, a passive-interface will neither send nor receive updates.
  • RIP Version 2 (RIPv2) R1# config t R1(config)# )#router rip R1(config)#network 192.168.10.0 R1(config)#network 192.168.20.0 R1(config)#version 2
  • Exercise - RIP Version 2 Configuration S0 S0 R1 R2 E0 E0 192.168.0.16/29 S0 S1 R3 192.168.0.4/30 192.168.0.8/30 192.168.0.32/28 1. Find out the IP Address and SNM of each interfaces A B
  • Exercise - RIP Version 2 Configuration S0 S0 R1 R2 E0 E0 192.168.0.18 255.255.255.248 S0 S1 R3 192.168.0.17 255.255.255.248 192.168.0.5 255.255.255.252 192.168.0.6 255.255.255.252 192.168.0.9 255.255.255.252 192.168.0.10 255.255.255.252 192.168.0.33 255.255.255.240 192.168.0.34 255.255.255.240 A B
  • Exercise - RIP Version 2 Configuration S0 S0 R1 R2 E0 E0 192.168.0.16/29 S0 S1 R3 192.168.0.4/30 192.168.0.8/30 192.168.0.32/28 R2# config t R2(config)#router rip R2(config)#network 192.168.0.4 R2(config)#network 192.168.0.8 R2(config)#version 2 R1# config t R1(config)# )#router rip R1(config)#network 192.168.0.4 R1(config)#network 192.168.0.16 R1(config)#version 2 R3# config t R3(config)# )#router rip R3(config)#network 192.168.0.8 R3(config)#network 192.168.0.32 R3(config)#version 2 A B
  • © 2002, Cisco Systems, Inc. All rights reserved. Enabling IGRP
      • CISCO Proprietary
      • More scalable than RIP
      • Sophisticated metric
    Introducing IGRP
      • Bandwidth
      • Delay
      • Reliability
      • Load
      • MTU
    IGRP Composite Metric
  • IGRP
    • Some of the IGRP key design characteristics emphasize the following:
      • It is a distance vector routing protocol.
      • Routing updates are broadcast every 90 seconds.
      • Bandwidth, load, delay and reliability are used to create a composite metric.
      • The main difference between RIP and IGRP configuration is that when you configure IGRP, you supply the autonomous system number. All routers must use the same number in order to share routing table information.
  • IGRP Vs RIP
  • IGRP Timers
    • Update timers these specify how frequently routing-update messages should be sent. The default is 90 seconds.
    • Invalid timers These specify how long a router should wait before declaring a route invalid if it doesn’t receive a specific update about it. The default is 3*90 = 270.
    • Holddown timers These specify the holddown period. The default is three times the update timer period plus 10 seconds. 280 seconds
    • Flush timers These indicate how much time should pass before a route should be flushed from the routing table. The default is seven times the routing update period. If the update timer is 90 seconds by default, then 7 × 90 = 630 seconds elapse before a route will be flushed from the route table.
  • Configuring IGRP
  • IGRP Configuration S0 S0 R1 R2 E0 E0 192.168.10.1 S0 S1 R3 R1# config t R1(config)# )#router igrp 10 R1(config)#network 192.168.10.0 R1(config)#network 192.168.20.0 R2# config t R2(config)#router igrp 10 R2(config)#network 192.168.20.0 R2(config)#network 192.168.30.0 192.168.10.2 192.168.20.1 192.168.20.2 192.168.30.1 192.168.30.2 192.168.40.1 192.168.40.2 R3# config t R3(config)# )#router igrp 10 R3(config)#network 192.168.30.0 R3(config)#network 192.168.40.0 A B
  • Verifying the IGRP Routing Tables
    • LabA# sh ip route
    • [output cut]
    • I 192.168.50.0 [100/170420] via 192.168.20.2, Serial0/0
    • I 192.168.40.0 [100/160260] via 192.168.20.2, Serial0/0
    • I 192.168.30.0 [100/158360] via 192.168.20.2, Serial0/0
    • C 192.168.20.0 is directly connected Serial0/0
    • C 192.168.10.0 is directly connected, FastEthernet0/0
    • The I means IGRP-injected routes. The 100 in [100/160360] is the administrative distance of IGRP. The 160,360 is the composite metric. The lower the composite metric, the better the route.
    • To delete all routes
    • clear ip route
  • Debug Commands
    • debug ip igrp events Command
      • summary of the IGRP routing information that is running on the network.
    • debug ip igrp transactions Command
      • shows message requests from neighbor routers asking for an update and the broadcasts sent from your router toward that neighbor router.
    • no debug all – to turn off all debug