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Ch. 16\Mod.7 – Distance Vector Routing Protocols Part 1 of 2: Distance Vector Routing and RIP

Ch. 16Mod.7 – Distance Vector Routing Protocols Part 1 of 2: Distance Vector Routing and RIP. CCNA 1 version 3.0. RIP routing process. Request for Comments (RFC) 1058

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Ch. 16\Mod.7 – Distance Vector Routing Protocols Part 1 of 2: Distance Vector Routing and RIP

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  1. Ch. 16\Mod.7 – Distance Vector Routing ProtocolsPart 1 of 2: Distance Vector Routing and RIP CCNA 1 version 3.0

  2. RIP routing process • Request for Comments (RFC) 1058 • RIP has evolved over the years from a Classful Routing Protocol, RIP Version 1 (RIP v1), to a Classless Routing Protocol, RIP Version 2 (RIP v2). RIP v2 enhancements include: • Ability to carry additional packet routing information. • Authentication mechanism to secure table updates. • Supports variable length subnet masking (VLSM).

  3. Configuring RIP

  4. Configuring RIP RIP and IGRP: • Classful network statements only • IOS will take subnetted networks but will translate it into the classful network for the running-config.

  5. Configuring RIP Clarifications (This is for IGPs only and not EGPs such as BGP): • The network command does two things: 1. Determines which interfaces will participate in sending and receiving routing updates, as long as the interface IP address falls in the range of the network command. 2. Determines which networks this router will announce as being directly connected to in its routing updates to other routers. • The network numbers do not necessarily have to be based on the network class, as it depends on the routing protocol. Network numbers are based on the network class for RIP, IGRP, and usually EIGRP, but can be more specific for OSPF, EIGRP and IS-IS.

  6. Triggered Extensions Triggered Extensions to RIP • http://www.cisco.com/en/US/products/sw/iosswrel/ps1830/products_feature_guide09186a008008746f.html • There were two problems using RIP to connect to a WAN: • Periodic broadcasting by RIP generally prevented WAN circuits from being closed. • Even on fixed, point-to-point links, the overhead of periodic RIP transmissions could seriously interrupt normal data transfer because of the quantity of information that hits the line every 30 seconds. • To overcome these limitations, triggered extensions to RIP cause RIP to send information on the WAN only when there has been an update to the routing database. • Periodic update packets are suppressed over the interface on which this feature is enabled. interface serial 0  ip rip triggered

  7. Triggered Extensions • RFC 2091, Triggered Extensions to RIP to Support Demand Circuits. • When triggered extensions to RIP are enabled, routing updates are transmitted on the WAN only if one of the following occurs: • The router receives a specific request for a routing update. (Full database is sent.) • Information from another interface modifies the routing database. (Only latest changes are sent) • The interface comes up or goes down. (Partial database is sent.) • The router is first powered on, to ensure that at least one update is sent. (Full database is sent.) • You might want to enable this feature if you are using an on-demand circuit and you are charged for usage time. Fewer routing updates will incur lower usage costs. interface serial 0  ip rip triggered

  8. Data Link Frame Header IP Packet Header UDP Segment Header RIP Message The RIPv1 Protocol RIP Message Data Link Frame ·MAC Source Address ·MAC Destination Address = Broadcast IP Packet ·IP Source Address ·IP Destination Address = Broadcast: 255.255.255.255 ·Protocol field = 17 for UDP UDP Segment ·Source Port number field = 520 for RIP Message RIP Message (Data portion of IP Packet): ·Routes: Network IP Address ·Hops (metric)

  9. Data Link Frame Header IP Packet Header UDP Segment Header RIP Message • Command: 1 signifying a Request or 2 signifying a Reply • Version: 1 for RIP v 1 or 2 for RIP v 2 • Address Family Identifier: 2 signifying IP (only exception is for a Request for the Router’s full routing table, later Semester in RIP v 2) • IP Address: The address of the destination route, which may be a network address, a subnet address of a host address. • Metric: Hop count between 1 and 16. Note: With RIP the sending router increases the metric before sending out the RIP message. • Note: The routing table knows the next-hop-ip-address (via) from the source IP address of the packet.

  10. RIP v2 message format • All the extensions to the original protocol are carried in the unused fields. • The Address Family Identifier (AFI) field is set to two for IP. The only exception is a request for a full routing table of a router or host, in which case it will be set to zero.

  11. RIP v2 message format • The Route Tag field provides a way to differentiate between internal and external routes. • External routes are those that have been redistributed into the RIP v2. • The Next Hop field contains the IP address of the next hop listed in the IP Address field. • Metric indicates how many internetwork hops, between 1 and 15 for a valid route, or 16 for an unreachable route.

  12. Configuring RIP RIP must be enabled and the networks specified. The remaining tasks are optional. Among these optional tasks are: • Applying offsets to routing metrics(Not commonly used) • Adjusting timers • Specifying a RIP version(RIPv1 or RIPv2) • Enabling RIP authentication • Configuring route summarization on an interface • Verifying IP route summarization • Disabling automatic route summarization(RIPv2) • Running IGRP and RIP concurrently(Usually, redistributing, not concurrently.) • Disabling the validation of source IP addresses • Enabling or disabling split horizon • Connecting RIP to a WAN

  13. ip classless command • IP classless only affects the operation of the forwarding processes in IOS. IP classless does not affect the way the routing table is built. • This command concerns classless and classful routing behavior, which is not the same as classless and classful routing protocols (later). • To discuss this command, we will use information which is not in the curriculum. • For more information: • The Routing Table: Part 1 or 2 - The Routing Table Structure (PDF)  • The Routing Table: Part 2 or 2 - The Routing Table Lookup Process (PDF) 

  14. Parent and Child Routes RouterB#show ip route 172.16.0.0/24 is subnetted, 3 subnets R 172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0 C 172.16.2.0 is directly connected, Serial0 C 172.16.3.0 is directly connected, FastEthernet0 C 192.168.1.0/24 is directly connected, Serial1 S 172.0.0.0/8 is directly connected, Serial1 S 160.0.0.0/4 is directly connected, Serial1 S* 0.0.0.0/0 is directly connected, Serial1 Parent Route • Created automatically whenever there is a route with a mask greater than the classful mask. • For non-VLSM routes, contains the mask of the child routes. Child Routes • Routes with masks greater than the default classful mask.

  15. Lookup what? RouterB#show ip route 172.16.0.0/24 is subnetted, 3 subnets R 172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0 C 172.16.2.0 is directly connected, Serial0 C 172.16.3.0 is directly connected, FastEthernet0 C 192.168.1.0/24 is directly connected, Serial1 S 172.0.0.0/8 is directly connected, Serial1 S 160.0.0.0/4 is directly connected, Serial1 S* 0.0.0.0/0 is directly connected, Serial1 Routing Table process matches: • The routing table process compares the left-most bits in the packet’s destination IP address with the left-most bits in the route in the routing table, looking for a longest-bit-match. • The subnet mask of the route in the routing table specifies the minimum number of left-most bits that must match. • Before checking child routes, the classful mask of the parent route is used. • For child routes the parent route’s mask is used. • For VLSM routes, the mask is contained with the child route.

  16. Parent and Child Routes RouterB#show ip route 172.16.0.0/24 is subnetted, 3 subnets R 172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0 C 172.16.2.0 is directly connected, Serial0 C 172.16.3.0 is directly connected, FastEthernet0 C 192.168.1.0/24 is directly connected, Serial1 S 172.0.0.0/8 is directly connected, Serial1 S 160.0.0.0/4 is directly connected, Serial1 S* 0.0.0.0/0 is directly connected, Serial1 DA = 192.168.1.10 • 16 bits of 172.16.0.0 do not match, so child routes are not checked. • 24 bits of 192.168.1.0/24 do match, so this route is used.

  17. Parent and Child Routes RouterB#show ip route 172.16.0.0/24 is subnetted, 3 subnets R 172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0 C 172.16.2.0 is directly connected, Serial0 C 172.16.3.0 is directly connected, FastEthernet0 C 192.168.1.0/24 is directly connected, Serial1 S 172.0.0.0/8 is directly connected, Serial1 S 160.0.0.0/4 is directly connected, Serial1 S* 0.0.0.0/0 is directly connected, Serial1 DA = 172.16.2.1 • 16 bits of 172.16.0.0 do match, so child routes are checked. • 24 bits of 172.16.1.0 do not match, so continue to next child route. • 24 bits of 172.16.2.0 do match, so this route is used!

  18. Parent and Child Routes RouterB#show ip route 172.16.0.0/24 is subnetted, 3 subnets R 172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0 C 172.16.2.0 is directly connected, Serial0 C 172.16.3.0 is directly connected, FastEthernet0 C 192.168.1.0/24 is directly connected, Serial1 S 172.0.0.0/8 is directly connected, Serial1 S 160.0.0.0/4 is directly connected, Serial1 S* 0.0.0.0/0 is directly connected, Serial1 DA = 32.1.1.10 • 16 bits of 172.16.0.0 do not match, so child routes are not checked. • 24 bits of 192.168.1.0/24 do not match, so this route is not used. • 8 bits of 172.0.0.0/8 do not match, so this route is not used. • 4 bits of 160.0.0.0/4 do not match, so this route is not used. • 0 bits of 0.0.0.0/0 does match, so this route is used!

  19. Parent and Child Routes RouterB#show ip route 172.16.0.0/24 is subnetted, 3 subnets R 172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0 C 172.16.2.0 is directly connected, Serial0 C 172.16.3.0 is directly connected, FastEthernet0 C 192.168.1.0/24 is directly connected, Serial1 S 172.0.0.0/8 is directly connected, Serial1 S 160.0.0.0/4 is directly connected, Serial1 S* 0.0.0.0/0 is directly connected, Serial1 DA = 172.16.4.1 • 16 bits of 172.16.0.0 do match, so child routes are checked. • 24 bits of 172.16.1.0 do not match, so continue to next child route. • 24 bits of 172.16.2.0 do not match, so continue to next child route. • 24 bits of 172.16.3.0 do not match, no more child routes. Now what??? It depends!

  20. Classful Routing Behavior RouterB#show ip route 172.16.0.0/24 is subnetted, 3 subnets R 172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0 C 172.16.2.0 is directly connected, Serial0 C 172.16.3.0 is directly connected, FastEthernet0 C 192.168.1.0/24 is directly connected, Serial1 S 172.0.0.0/8 is directly connected, Serial1 S 160.0.0.0/4 is directly connected, Serial1 S* 0.0.0.0/0 is directly connected, Serial1 DA = 172.16.4.1 Router(config)# no ip classless • With classful routing behavior, if the child routes are checked but there are no matches, the routing lookup process ends and the Packet is dropped. (The packets get in, but they can’t get out!) • Supernet and default routes are not checked. • Default with IOS 11.2 and prior

  21. Classless Routing Behavior RouterB#show ip route 172.16.0.0/24 is subnetted, 3 subnets R 172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0 C 172.16.2.0 is directly connected, Serial0 C 172.16.3.0 is directly connected, FastEthernet0 C 192.168.1.0/24 is directly connected, Serial1 S 172.0.0.0/8 is directly connected, Serial1 S 160.0.0.0/4 is directly connected, Serial1 S* 0.0.0.0/0 is directly connected, Serial1 DA = 172.16.4.1 Router(config)# ip classless • With classless routing behavior, if the child routes are checked but there are no matches, the routing lookup process continues with other routes in the routing table, including supernet and default routes. • 8 bits of 172.0.0.0/8 do match, so this route is used! • Default with IOS 11.3 and later

  22. Common RIP Configuration Issues Split Horizon • The following command is used to disable split horizon: GAD(config-if)#no ip split-horizon • The following command is used to enable (default) split horizon: GAD(config-if)#ip split-horizon

  23. Common RIP Configuration Issues Holddown Timer • The ideal setting would be to set the timer just longer that the longest possible update time for the internetwork. • To change the holddown timer: Router(config-router)#timers basicupdate invalid holddown flush [sleeptime]

  24. Common RIP Configuration Issues Update Timer • The default RIP update interval in Cisco IOS is 30 seconds. This can be configured for longer intervals to conserve bandwidth, or for shorter intervals to decrease convergence time. • To change the update internal: GAD(config-router)#update-timer seconds

  25. Common RIP Configuration Issues For RIP and IGRP, the passive interface command stops the router from sending updates to a particular neighbor, but the router continues to listen and use routing updates from that neighbor. (More later.) • Also used when there are no routers on that interface, such as stub LANs. Router(config-router)# passive-interface interface router rip passive-interface fastethernet 0/0 

  26. Common RIP Configuration Issues • Because RIP is a broadcast protocol, the network administrator may have to configure RIP to exchange routing information in a non-broadcast network such as Frame Relay. • In this type of network, RIP needs to be told of other neighboring RIP routers. • To do this use the router rip command: Router(config-router)# neighbor ip address

  27. Common RIP Configuration Issues • By default, the Cisco IOS software receives RIP Version 1 and Version 2 packets, but sends only Version 1 packets. • The network administrator can configure the router to only receive and send Version 1 packets or the administrator can configure the router to send only Version 2 packets.

  28. Compatibility with RIP v1 NewYork interface fastethernet0/0 ip address 192.168.50.129 255.255.255.192 ip rip send version 1 ip rip receive version 1 interface fastethernet0/1 ip address 172.25.150.193 255.255.255.240 ip rip send version 1 2 interface fastethernet0/2 ip address 172.25.150.225 225.255.255.240 router rip version 2 network 172.25.0.0 network 192.168.50.0 RIPv2 • Interface FastEthernet0/0 is configured to send and receive RIP v1 updates. • FastEthernet0/1 is configured to send both version 1 and 2 updates. • FastEthernet0/2 has no special configuration and therefore sends and receives version 2 by default.

  29. Verifying RIP configuration

  30. Verifying RIP configuration • Also: show running-config

  31. Troubleshooting RIP update issues

  32. Troubleshooting RIP update issues Other commands to troubleshoot RIP: • show ip rip database • show ip protocols {summary} • show ip route • debug ip rip {events} • show ip interface brief

  33. Load balancing with RIP • RIP is capable of load balancing over as many as six equal-cost paths, with four paths being default. RIP performs what is referred to as “round robin” load balancing. • This means that RIP takes turns forwarding packets over the parallel paths. • This is only part of the story…

  34. Fast Switching and Process Switching The following information is taken from Routing TCP/IP Volume I by Jeff Doyle. • Load sharing or Load balancing allows routers to take advantage of multiple paths to the same destination. • Equal-cost load balancing: • Distributes packets equally among multiple paths with equal metrics • RIP, IGRP, EIGRP, OSPF, IS-IS and BGP • Unequal-cost load balancing: • Distributes packets among multiple paths with different metrics, inversely proportional to the cost of the routes. • EIGRP • Load sharing can be either: • Per Destination (Fast Switching) • Per Packet ( Process Switching)

  35. Fast Switching – Per Destination Load Balancing • The default for most interfaces is Fast Switching. • Load balancing is distributed according to the destination IP address. • Given two paths to the same network, all packets for one destination IP address will travel over the first path, all packets for a second destination will travel over the second path, all packets for the third destination will again travel over the first path, and so on. • To enable fast switching: Router(config-if)# ip route-cache • To enable distributed or process switching: Router(config-if)# noip route-cache Router(config-if)# ip route-cache ping 10.0.0.1 ping 10.0.0.2

  36. Fast Switching – Per Destination Load Balancing Fast Switching • Router switches first packet to a particular destination, a routing table lookup is performed and an exit interface is selected. • The necessary data-link information to frame the packet for the selected interface is retrieved including any ARP cache information. • The route and data-link information is stored in fast switching cache. • The router uses the cache to look up subsequent packets. • All other packets to the same destination are immediately switched out the same interface without the router performing another routing table lookup, including any recursive lookups. (Also no ARP cache lookup). Router(config-if)# ip route-cache ping 10.0.0.1 ping 10.0.0.2

  37. Process Switching – Per Packet Load Balancing Process Switching • Given equal cost paths, per packet load sharing means that one packet to a destination is sent over one link, the next packet to the same destination is sent over the next link, and so on. • If the paths are unequal cost, the load balancing may be one packet over the higher-cost link for every three packets over the lower-cost link, or similar ratio. • With process switching, for every packet, the router performs a route table lookup and selects an interface, and looks up the data-link information. • To enable distributed or process switching: Router(config-if)# noip route-cache Router(config-if)#noip route-cache ping 10.0.0.1 ping 10.0.0.2

  38. Which one? Fast Switching or Process Switching • Process switching (per packet load balancing) has a price, load balancing may be distributed more evenly but the lower switching time and processor utilization of fast switching are lost. Fast Switching Process Switching ping 10.0.0.1 ping 10.0.0.1 ping 10.0.0.2 ping 10.0.0.2 Router(config-if)# ip route-cache Router(config-if)#noip route-cache

  39. Using debug ip packet withFast Switching and Process Switching Router# debug ip packet IP: s=192.168.3.2 (FastEthernet0), d=10.0.0.1 (Serial0/0), g=192.168.1.2, forward IP: s=192.168.3.2 (FastEthernet0), d=10.0.0.1 (Serial0/1), g=192.168.2.2, forward IP: s=192.168.3.2 (FastEthernet0), d=10.0.0.1 (Serial0/0), g=192.168.1.2, forward IP: s=192.168.3.2 (FastEthernet0), d=10.0.0.1 (Serial0/1), g=192.168.2.2, forward • debug ip packet can be used to observe packets sent and received and the interfaces that are involved. • IMPORTANT: The debug ip packet command allows only process switched packets to be observed. Fast switch packets are not displayed (except for the first packet in the flow).

  40. Load balancing across multiple paths • Note: The example used in this section of the online curriculum is really for IGRP/EIGRP and does not fit well in this section of RIP. • By default, most IP routing protocols install a maximum of four parallel routes in a routing table. • Static routes always install six routes. • The exception is BGP, which by default allows only one path to a destination. • The range of maximum paths is one to six paths. To change the maximum number of parallel paths allowed, use the following command in router configuration mode: Router(config-router)#maximum-paths [number]

  41. RIP and Administrative Distance

  42. RIP and Floating Static Routes • Floating static routes are static routes which are used as backup routes. • They are only injected into the routing table when a route with a lower administrative distance (dynamic or another static route) goes down. • Should the route with the lower administrative distance come back up then the floating static route is removed from the routing table. 172.16.0.0/16 X router rip network 192.168.14.0 ip route 172.16.0.0 255.255.0.0 bri0/1 130

  43. Redistribute Static • Redistributes static routes into the dynamic routing domain. • 172.16.0.0/16 will be seen by other RIP routers as a dynamic route learned via RIP. • The default metric is 0, so B and D will have a hop count of 1, where C will have a hop count of 2. 172.16.0.0/16 RouterA ip route 172.16.0.0 255.255.0.0 eth 0 Router rip redistribute static network …. RIP

  44. RIPv1 Labs – 3 Scenarios • Read the following lab. • In groups review the configurations and the outputs. • Afterwards, we will discuss the this lab together, paying particular attention to the Reflection sections.

  45. RIPv1 Labs – 3 Scenarios Objective • In this lab, you will configure RIP routing in three different scenarios. • At the end of each scenario, all hosts and all routers should be able to reach (ping) each other. Scenario There are five separate classful networks. After configuring RIP, we want to view the RIP update messages being sent and received by each router. • Scenario 1: Running RIPv1 on classful networks • Scenario 2: Running RIPv1 on subnets and between classful networks • Scenario 3: Running RIPv1 on a stub network These three scenarios can be done in sequence or separately.

  46. RIPv1 Labs – 3 Scenarios Setup • Use the 8 Steps to Success to help you configure the routers. • Be sure your cabling is correct, as this causes more troubleshooting issues than anything else. • If the routers have a startup-config already on them, erase it and reboot the routers. • Configure the routers to include hostnames and the proper interface commands including IP addresses, subnet masks, etc. • Each router should be able to ping the interface of the adjacent (neighboring) router and the host on its LAN (Ethernet) interface. • Test and troubleshoot as necessary. Basic Configurations • There is a Basic Configuration included for each scenario, but it does not include clock rate, no shutdown and some other necessary commands. • Note: Even though some of the networks are in numerical order, obviously this does not need to be the case. We only did this to make it easier to remember where the networks originated from.

  47. RIPv1 Labs – 3 Scenarios Optional: Keeping outputs from interrupting our inputs Before we begin to configure RIP, lets configure the console 0 port to keep debug and other output messages from interrupting our input. Use the following command on each router to keep the debug out from interfering with you command-line input: Router(config)# line console 0 Router(config-line)# loggingsynchronous Optional: Changing the default timeout After 10 minutes, by default, if there is no input via the console, the user will be logged off. Although a good idea in production environment, in a lab environment this can be somewhat annoying. To turn-off the automatic timeout feature, we use the command: exec-timeout minutes [seconds], setting both the minutes and seconds to 0. Router(config)# line console 0 Router(config-line)# exec-timeout 0 0

  48. Scenario 1: Running RIPv1 on classful networks SanJose2 hostname SanJose2 interface ethernet 0 ip add 192.168.1.1 255.255.255.0 interface serial 0 ip add 192.168.2.1 255.255.255.0 SanJose1 hostname SanJose1 interface ethernet 0 ip add 192.168.3.1 255.255.255.0 interface serial 0 ip add 192.168.2.2 255.255.255.0 interface serial 1 ip add 192.168.4.2 255.255.255.0 Baypointe hostname Baypointe interface ethernet 0 ip add 192.168.5.1 255.255.255.0 interface serial 0 ip add 192.168.4.1 255.255.255.0

  49. Scenario 1: Running RIPv1 on classful networks Objective: Running RIPv1 on classful networks This scenario is the same one we used in the network discovery lab, with the same configurations and the same outputs. The concepts specific to this scenario will become more clear when we view the differences between this scenario and Scenario 2: Running RIPv1 on subnets and between classful networks. Step 1 – Configuring RIP First, lets enable RIP on each router. From global configuration you will enter the command (the default is RIPv1): Router(config)#router rip Once you are in the Router RIP configuration sub-mode, all you need to do is enter the classful network address for each directly connected network, using the network command. Router(config-router)#network directly-connected-classful-network-address

  50. Scenario 1: Running RIPv1 on classful networks Here are the commands for each router: SanJose2#configure terminal Enter configuration commands, one per line. End with CNTL/Z. SanJose2(config)#router rip SanJose2(config-router)#network 192.168.1.0 SanJose2(config-router)#network 192.168.2.0 Baypointe#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Baypointe(config)#router rip Baypointe(config-router)#network 192.168.4.0 Baypointe(config-router)#network 192.168.5.0 SanJose1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. SanJose1(config)#router rip SanJose1(config-router)#network 192.168.2.0 SanJose1(config-router)#network 192.168.3.0 SanJose1(config-router)#network 192.168.4.0

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