CCNA 2 Chapter 3 Dynamic Routing

level 1 parent route

, the 172.16.0.0 and 209.165.200.0 routes are level 1 parent routes. A parent route is a level 1 network route that is subnetted. A parent route can never be an ultimate route. the level 1 parent routes in the routing table of R1. In the routing table, it basically provides a heading for the specific subnets it contains. Each entry displays the classful network address, the number of subnets and the number of different subnet masks into which the classful address has been subdivided.

RIPv2 (Routing Information Protocol version 2)

A Cisco proprietary hybrid protocol that uses "hello" packets broadcasted every 60 seconds to form neighbor relationships, has metrics of bandwidth, delay, load, reliability and MTU, is classless (uses VLSM), can support different protocols with PDMs and implements DUAL as it's algorithm to choose best paths to networks

Routing Table Terms

A dynamically built routing table provides a great deal of information, as shown in the figure. Therefore, it is crucial to understand the output generated by the routing table. Special terms are applied when discussing the contents of a routing table. The Cisco IP routing table is not a flat database. The routing table is actually a hierarchical structure that is used to speed up the lookup process when locating routes and forwarding packets. Within this structure, the hierarchy includes several levels. Routes are discussed in terms of: Ultimate route Level 1 route Level 1 parent route Level 2 child routes

Level 1 route

A level 1 route is a route with a subnet mask equal to or less than the classful mask of the network address. Therefore, a level 1 route can be a: Network route - A network route that has a subnet mask equal to that of the classful mask. Supernet route - A supernet route is a network address with a mask less than the classful mask, for example, a summary address. Default route - A default route is a static route with the address 0.0.0.0/0. The source of the level 1 route can be a directly connected network, static route, or a dynamic routing protocol.

Intermediate System to Intermediate System (IS-IS)

A link-state routing protocol similar in its operation to OSPF. IS-IS uses a configurable, yet dimensionless, metric associated with an interface and runs Dijkstra's shortest path first algorithm. Although using IS-IS as an IGP offers the scalability, fast convergence, and vendor interoperability benefits of OSPF, it has not been deployed as widely as OSPF.

Exterior Gateway Protocol (EGP)

A routing protocol that operates between autonomous systems, which are networks under different administrative control. Border Gateway Protocol (BGP) is the only EGP in widespread use today.

Static Routing Advantages and Disadvantages

Advantages Easy to implement in a small network Very secure. No advertisements are set as compared to dynamic protocols Route to destination is always the same. No routing algorithm is or update mechanism required; therefore extra resources (CPU or RAM) are not required. Disadvantages Suitable only for simple topologies or for special purposes such as default static route. Configuration complexity increases dramatically as network grows. Manual intervention required to re-route traffic.

Dynamic Routing Advantages and Disadvantages

Advantages Suitable in all topologies where multiple routers are required. Generally independent of network size. Automatically adapts topology to reroute traffic if possible. Disadvantages Can be more complex to implement. Less secure. Additional configuration settings are required to secure. Route depends on the current topology. Requires additional CPU, RAM and link bandwidth.

Router RIP Configuration Mode

Although RIP is rarely used in modern networks, it is useful as a foundation for understanding basic network routing. This section provides a brief overview of how to configure basic RIP settings and how to verify RIPv2. Refer to the reference topology in Figure 1 and the addressing table in Figure 2. In this scenario, all routers have been configured with basic management features and all interfaces identified in the reference topology are configured and enabled. There are no static routes configured and no routing protocols enabled; therefore, remote network access is currently impossible. RIPv1 is used as the dynamic routing protocol. To enable RIP, use the router rip command, as shown in Figure 3. This command does not directly start the RIP process. Instead, it provides access to the router configuration mode where the RIP routing settings are configured. When enabling RIP, the default version is RIPv1. To disable and eliminate RIP, use the no router rip global configuration command. This command stops the RIP process and erases all existing RIP configurations.

OSPF (Open Shortest Path First)

An IGP and link-state routing protocol that makes up for some of the limitations of RIP and can coexist with RIP on a network.

Ultimate route

An ultimate route is a routing table entry that contains either a next-hop IPv4 address or an exit interface. Directly connected, dynamically learned, and local routes are ultimate routes.

Static Routing Uses

Before identifying the benefits of dynamic routing protocols, consider the reasons why network professionals use static routing. Dynamic routing certainly has several advantages over static routing; however, static routing is still used in networks today. In fact, networks typically use a combination of both static and dynamic routing. Static routing has several primary uses, including: Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly. Routing to and from a stub network, which is a network with only one default route out and no knowledge of any remote networks. Accessing a single default route (which is used to represent a path to any network that does not have a more specific match with another route in the routing table).

BGP-4 (Border Gateway Protocol)

Border Gateway Protocol 4 (BGP-4) ... Abstract This document, together with its companion document, "Application of the Border Gateway Protocol in the Internet", define an inter- autonomous system routing protocol for the Internet.

Configure Passive Interfaces

By default, RIP updates are forwarded out all RIP-enabled interfaces. However, RIP updates really only need to be sent out interfaces that are connected to other RIPenabled routers. For instance, refer to the topology in Figure 1. RIP sends updates out of its G0/0 interface even though no RIP device exists on that LAN. R1 has no way of knowing this and, as a result, sends an update every 30 seconds. Sending out unneeded updates on a LAN impacts the network in three ways: Wasted Bandwidth - Bandwidth is used to transport unnecessary updates. Because RIP updates are either broadcasted or multicasted, switches also forward the updates out all ports. Wasted Resources - All devices on the LAN must process the update up to the transport layers, at which point the devices will discard the update. Security Risk - Advertising updates on a broadcast network is a security risk. RIP updates can be intercepted with packet sniffing software. Routing updates can be modified and sent back to the router, corrupting the routing table with false metrics that misdirect traffic. Use the passive-interface router configuration command to prevent the transmission of routing updates through a router interface, but still allow that network to be advertised to other routers. The command stops routing updates out the specified interface. However, the network that the specified interface belongs to is still advertised in routing updates that are sent out other interfaces. There is no need for R1, R2, and R3 to forward RIP updates out of their LAN interfaces. The configuration in Figure 2 identifies the R1 G0/0 interface as passive. The show ip protocols command is then used to verify that the Gigabit Ethernet interface was passive. Notice that the G0/0 interface is no longer listed as sending or receiving version 2 updates, but instead is now listed under the Passive Interface(s) section. Also notice that the network 192.168.1.0 is still listed under Routing for Networks, which means that this network is still included as a route entry in RIP updates that are sent to R2. Note: All routing protocols support the passive-interface command. Use the Syntax Checker in Figure 3 to configure the LAN interface as a passive interface on R2 and R3. As an alternative, all interfaces can be made passive using the passive-interface default command. Interfaces that should not be passive can be re-enabled using the no passive-interface command.

Advertise Networks

By entering the RIP router configuration mode, the router is instructed to run RIPv1. But the router still needs to know which local interfaces it should use for communication with other routers, as well as which locally connected networks it should advertise to those routers. To enable RIP routing for a network, use the network network-address router configuration mode command. Enter the classful network address for each directly connected network. This command: Enables RIP on all interfaces that belong to a specific network. Associated interfaces now both send and receive RIP updates. Advertises the specified network in RIP routing updates sent to other routers every 30 seconds. Note: RIPv1 is a classful routing protocol for IPv4. Therefore, if a subnet address is entered, the IOS automatically converts it to the classful network address. For example, entering the network 192.168.1.32 command would automatically be converted to network 192.168.1.0 in the running configuration file. The IOS does not give an error message, but instead corrects the input and enters the classful network address.

IPv6 Routing Table Entries

Components of the IPv6 routing table are very similar to the IPv4 routing table. For instance, it is populated using directly connected interfaces, static routes, and dynamically learned routes. Because IPv6 is classless by design, all routes are effectively level 1 ultimate routes. There is no level 1 parent of level 2 child routes. The topology displayed in the figure is used as the reference topology for this section. Notice that in the topology: R1, R2, and R3 are configured in a full mesh topology. All routers have redundant paths to various networks. R2 is the edge router and connects to the ISP; however, a default static route is not being advertised. EIGRP for IPv6 has been configured on all three routers. Note: Although EIGRP for IPv6 is used to populate the routing tables, the operation and configuration of EIGRP is beyond the scope of this course.

Advertise the RIP network

Configure RIP on R2 to advertise the appropriate networks based on the topology. Start with the lowest IP network. R2(config)# router rip R2(config-router)# network 192.168.2.0 R2(config-router)# network 192.168.3.0 R2(config-router)# network 192.168.4.0 You are now logged into R3. Advertise the RIP networks for R3. Start with the lowest IP network. R3(config)# router rip R3(config-router)# network 192.168.4.0 R3(config-router)# network 192.168.5.0 You successfully configured the networks for R2 and R3.

Configure and verify Passive Interfaces

Configure passive interface on G0/0 and return to privileged EXEC mode. R2(config)# router rip R2(config-router)# passive-interface g0/0 R2(config-router)# end R2# *Mar 10 16:33:32.391: %SYS-5-CONFIG_I: Configured from console by console Verify the RIP protocol settings on R2. R2# show ip protocols *** IP Routing is NSF aware *** Routing Protocol is "rip" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Sending updates every 30 seconds, next due in 17 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Redistributing: rip Default version control: send version 2, receive version 2 Interface Send Recv Triggered RIP Key-chain Serial0/0/0 2 2 Serial0/0/1 2 2 Automatic network summarization is not in effect Maximum path: 4 Routing for Networks: 192.168.2.0 192.168.3.0 192.168.4.0 Passive Interface(s): GigabitEthernet0/0 Routing Information Sources: Gateway Distance Last Update 192.168.2.1 120 00:00:24 Gateway Distance Last Update 192.168.4.1 120 00:00:23 Distance: (default is 120) R2# You are now logged into R3. Configure passive interface to be the default setting. Remove the passive interface setting from S0/0/1 and return to privileged EXEC mode. R3(config)# router rip R3(config-router)# passive-interface default R3(config-router)# no passive-interface s0/0/1 R3(config-router)# end R3# *Mar 10 16:34:28.899: %SYS-5-CONFIG_I: Configured from console by console Verify the RIP protocol settings on R3. R3# show ip protocols *** IP Routing is NSF aware *** Routing Protocol is "rip" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Sending updates every 30 seconds, next due in 15 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Redistributing: rip Default version control: send version 2, receive version 2 Interface Send Recv Triggered RIP Key-chain Serial0/0/1 2 2 Automatic network summarization is not in effect Maximum path: 4 Routing for Networks: 192.168.4.0 192.168.5.0 Passive Interface(s): Embedded-Service-Engine0/0 GigabitEthernet0/0 GigabitEthernet0/1 GigabitEthernet0/3 Serial0/0/0 RG-AR-IF-INPUT1 Routing Information Sources: Gateway Distance Last Update 192.168.4.2 120 00:00:23 Distance: (default is 120) R3# You successfully configured and verified passive interface on R2 and R3.

Interior Gateway Routing Protocol (IGRP)

Created to overcome some of RIP's shortcomings, including the maximum hop count of 16

Disable Auto Summarization

Disable automatic summarization on R2 and return to privileged EXEC mode. R2(config)# router rip R2(config-router)# no auto-summary R2(config-router)# end R2# *Mar 10 14:16:10.439: %SYS-5-CONFIG_I: Configured from console by console Verify the RIP protocol settings on R2. R2# show ip protocols *** IP Routing is NSF aware *** Routing Protocol is "rip" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Sending updates every 30 seconds, next due in 19 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Redistributing: rip Default version control: send version 2, receive version 2 Interface Send Recv Triggered RIP Key-chain GigabitEthernet0/0 2 2 Serial0/0/0 2 2 Serial0/0/1 2 2 Automatic network summarization is not in effect Maximum path: 4 Routing for Networks: 192.168.2.0 192.168.3.0 192.168.4.0 Routing Information Sources: Gateway Distance Last Update 192.168.2.1 120 00:00:09 192.168.4.1 120 00:00:01 Distance: (default is 120) R2# You are now logged into R3. Disable automatic summarization on R3 and return to privileged EXEC mode. R3(config)# router rip R3(config-router)# no auto-summary R3(config-router)# end R3# *Mar 10 14:17:06.059: %SYS-5-CONFIG_I: Configured from console by console Verify the RIP protocol settings on R3. R3# show ip protocols *** IP Routing is NSF aware *** Routing Protocol is "rip" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Sending updates every 30 seconds, next due in 11 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Redistributing: rip Default version control: send version 2, receive version 2 Interface Send Recv Triggered RIP Key-chain GigabitEthernet0/0 2 2 Serial0/0/1 2 2 Automatic network summarization is not in effect Maximum path: 4 Routing for Networks: 192.168.4.0 192.168.5.0 Routing Information Sources: Gateway Distance Last Update 192.168.4.2 120 00:00:26 Distance: (default is 120) R3# You successfully disabled automatic summarization on R2 and R3.

Compare Static and Dynamic Routing

Dynamic Routing Suitable for multiple topologies Adapts to topology changes to reroute traffic, when possible. Requires more CPU, RAM and link bandwidth Static route Easy to implement in small network Route to the destination is always the same.

Dynamic Routing Protocol Evolution

Dynamic routing protocols have been used in networks since the late 1980s. One of the first routing protocols was RIP. RIPv1 was released in 1988, but some of the basic algorithms within the protocol were used on the Advanced Research Projects Agency Network (ARPANET) as early as 1969. As networks evolved and became more complex, new routing protocols emerged. The RIP protocol was updated to RIPv2 to accommodate growth in the network environment. However, RIPv2 still does not scale to the larger network implementations of today. To address the needs of larger networks, two advanced routing protocols were developed: Open Shortest Path First (OSPF) and Intermediate System-to-Intermediate System (IS-IS). Cisco developed the Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP (EIGRP), which also scales well in larger network implementations. Additionally, there was the need to connect different internetworks and provide routing between them. The Border Gateway Protocol (BGP) is now used between Internet service providers (ISPs). BGP is also used between ISPs and their larger private clients to exchange routing information. Figure 1 displays the timeline of when the various protocols were introduced. Figure 2 classifies the protocols. With the advent of numerous consumer devices using IP, the IPv4 addressing space is nearly exhausted; thus, IPv6 has emerged. To support the communication based on IPv6, newer versions of the IP routing protocols have been developed, as shown in the IPv6 row in the Figure 2.

Dynamic Routing Protocols Uses

Dynamic routing protocols help the network administrator manage the time-consuming and exacting process of configuring and maintaining static routes. Imagine maintaining the static routing configurations for the seven routers hat if the company grew and now had four regions and 28 routers to manage, What happens when a link goes down? How do you ensure that redundant paths are available? Dynamic routing is the best choice for large networks

Enable and Verify RIPv2

Enable RIP version 2 on R2 and return to privileged EXEC mode. R2(config)# router rip R2(config-router)# version 2 R2(config-router)# end R2# *Mar 10 13:48:38.951: %SYS-5-CONFIG_I: Configured from console by console Verify the RIP protocol settings on R2. R2# show ip protocols *** IP Routing is NSF aware *** Routing Protocol is "rip" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Sending updates every 30 seconds, next due in 26 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Redistributing: rip Default version control: send version 2, receive version 2 Interface Send Recv Triggered RIP Key-chain GigabitEthernet0/0 2 2 Serial0/0/0 2 2 Serial0/0/1 2 2 Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 192.168.2.0 192.168.3.0 192.168.4.0 Routing Information Sources: Gateway Distance Last Update 192.168.2.1 120 00:00:19 192.168.4.1 120 00:00:22 Distance: (default is 120) Display the routing table on R2. R2# show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per- user static route o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP + - replicated route, % - next hop override Gateway of last resort is not set R 192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:03, Serial0/0/0 192.168.2.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.2.0/24 is directly connected, Serial0/0/0 L 192.168.2.2/32 is directly connected, Serial0/0/0 192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.3.0/24 is directly connected, GigabitEthernet0/0 L 192.168.3.1/32 is directly connected, GigabitEthernet0/0 192.168.4.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.4.0/24 is directly connected, Serial0/0/1 L 192.168.4.2/32 is directly connected, Serial0/0/1 R2# You are now logged into R3. Enable RIP version 2 on R3 and return to privileged EXEC mode. R3(config)# router rip R3(config-router)# version 2 R3(config-router)# end R3# *Mar 10 13:50:17.359: %SYS-5-CONFIG_I: Configured from console by console Verify the RIP protocol settings on R3. R3# show ip protocols *** IP Routing is NSF aware *** Routing Protocol is "rip" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Sending updates every 30 seconds, next due in 18 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Redistributing: rip Default version control: send version 2, receive version 2 Interface Send Recv Triggered RIP Key-chain GigabitEthernet0/0 2 2 Serial0/0/1 2 2 Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 192.168.4.0 192.168.5.0 Routing Information Sources: Gateway Distance Last Update 192.168.4.2 120 00:00:20 Distance: (default is 120) Display the routing table on R3. R3# show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per- user static route o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP + - replicated route, % - next hop override Gateway of last resort is not set R 192.168.1.0/24 [120/2] via 192.168.4.2, 00:00:03, Serial0/0/1 R 192.168.2.0/24 [120/1] via 192.168.4.2, 00:00:03, Serial0/0/1 R 192.168.3.0/24 [120/1] via 192.168.4.2, 00:00:03, Serial0/0/1 192.168.4.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.4.0/24 is directly connected, Serial0/0/1 L 192.168.4.1/32 is directly connected, Serial0/0/1 192.168.5.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.5.0/24 is directly connected, GigabitEthernet0/0 L 192.168.5.1/32 is directly connected, GigabitEthernet0/0 R3# You successfully enable and verified RIPv2 on R2 and R3.

Routing Protocol Evolution

Exterior Gateway Protocol (EGP) (1982) Interior Gateway routing protocol (IGRP) (1985) Routing information protocol (RIPv1) (1988) Open Short path first (OSPF) (1989) Intermediate System-to-intermediate System (IS-IS) (1990) Open Short Path First V2 (OFPFv2) (1991) Enhanced Interior Gateway routing protocol (EIGRP) (1992) Routing information protocol v2 (RIPv2) (1993) Border Gateway protocol version 4 (BGP-4) (1995) Ripng (1997) Open Short Path First v3 (OSPFv3) (1999) Border Gateway protocol version 4 multi protocol Extensions (BGP-MP) (1999) Intermediate System-to-intermediate System for IPv6 (IS-IS for IPv6) (2000) Enhanced Interior Gateway routing protocol for IPv6 (EIGRP for IPv6) (2005)

Open Shortest Path First (OSPF) protocol version 2

Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous system (AS). It is defined as OSPF Version 2 in RFC 2328 (1998) for IPv4.

routing table entries

R1# show ip route | begin gateway

Routing information protocol (RIPv1)

RIP is a distance-vector routing protocol using "hop count" as a routing metric. The maximum number of hops allowed for RIP is 15 which effectively limits the size of networks that RIP can support.

Disable Auto Summarization

RIPv2 automatically summarizes networks at major network boundaries by default, just like RIPv1. To modify the default RIPv2 behavior of automatic summarization, use the no auto-summary router configuration mode command as shown in Figure 2. This command has no effect when using RIPv1. When automatic summarization has been disabled, RIPv2 no longer summarizes networks to their classful address at boundary routers. RIPv2 now includes all subnets and their appropriate masks in its routing updates. The show ip protocols now states that "automatic network summarization is not in effect". Note: RIPv2 must be enabled before automatic summarization is disabled.

Parts of an IPv6 Routing Table Entry

Route Source. Administrative Distance. Outgoing interface Connected. 0. Serial 0/0/0 EIGRP. 90. Serial 0/0/1 Local Route. 0. Gigabit Ethernet 0/0

Parts of an IPv4 Routing Table Entry

Route. Route source AD. metric 10.4.0.0/16. Static. 1. 0 172.16.2.0/24. Connected. 0. 0 172.16.3.0/24. EIGRP. 90. 2172416 192.168.110.0/24. OSPF. 110. 65 192.168.120.0/24. RIP 120. 1

RIPng

Routing Information Protocol next generation

Propagate a Default Route

Similar default static routes could be configured on R2 and R3, but it is much more scalable to enter it one time on the edge router R1 and then have R1 propagate it to all other routers using RIP. To provide Internet connectivity to all other networks in the RIP routing domain, the default static route needs to be advertised to all other routers that use the dynamic routing protocol. To propagate a default route in RIP, the edge router must be configured with: A default static route using the ip route 0.0.0.0 0.0.0.0 command. The default-information originate router configuration command. This instructs R1 to originate default information, by propagating the static default route in RIP updates. The example in Figure 2 configures a fully-specified default static route to the service provider and then the route is propagated by RIP. Notice that R1 now has a Gateway of Last Resort and default route installed in its routing table.

Parent and Child IPv4 Routes

Specified network. Route Type 0.0.0.0. Level 1 192.168.3.0/24. Level 1 192.0.2.64/26. Level 2 child 192.0.3.0/30. Level 2 child 192.0.2.0.24. Level 1 parent

Directly Connected Entries

The entries contain the following information: Route source - Identifies how the route was learned. Directly connected interfaces have two route source codes. C identifies a directly connected network. Directly connected networks are automatically created whenever an interface is configured with an IP address and activated. L identifies that this is a local route. Local routes are automatically created whenever an interface is configured with an IP address and activated. Destination network - The address of the remote network and how that network is connected. Outgoing interface - Identifies the exit interface to use when forwarding packets to the destination network. A router typically has multiple interfaces configured. The routing table stores information about both directly connected and remote routes. As with directly connected networks, the route source identifies how the route was learned. For instance, common codes for remote networks include: S - Identifies that the route was manually created by an administrator to reach a specific network. This is known as a static route. D - Identifies that the route was learned dynamically from another router using the EIGRP routing protocol. O - Identifies that the route was learned dynamically from another router using the OSPF routing protocol. R - Identifies that the route was learned dynamically from another router using the RIP routing protocol.

Remote Network Entries

The entry identifies the following information: Route source - Identifies how the route was learned. Destination network - Identifies the address of the remote network. Administrative distance (AD) - Identifies the trustworthiness of the route source. The AD for static routes is 1 and the AD for connected routes is 0. Dynamic routing protocols have an AD higher than 1 depending upon the protocol. Metric - Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. The metric for static and connected routes is 0. Next hop - Identifies the IPv4 address of the next router to forward the packet to. Route timestamp - Identifies from when the route was last heard. Outgoing interface - Identifies the exit interface to use to forward a packet toward the final destination.

Verify RIP Routing

The show ip protocols command displays the IPv4 routing protocol settings currently configured on the router. 1. RIP routing is configured and running on router R1. 2. The values of various timers; for example, the next routing update, is sent by R1 in 16 seconds. 3. The version of RIP configured is currently RIPv1. 4. R1 is currently summarizing at the classful network boundary. 5. The classful networks are advertised by R1. These are the networks that R1 includes in its RIP updates. 6. The RIP neighbors are listed, including their next-hop IP address, the associated AD that R2 uses for updates sent by this neighbor, and when the last update was received from this neighbor. Note: This command is also very useful when verifying the operations of other routing protocols (i.e., EIGRP and OSPF). The show ip route command displays the RIP routes installed in the routing table.

Verify RIP Settings and Routes

Verify the networks being advertised in RIP on router R2. R2# show ip protocols *** IP Routing is NSF aware *** Routing Protocol is "rip" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Sending updates every 30 seconds, next due in 16 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Redistributing: rip Default version control: send version 1, receive any version Interface Send Recv Triggered RIP Key-chain GigabitEthernet0/0 1 1 2 Serial0/0/0 1 1 2 Serial0/0/1 1 1 2 Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 192.168.2.0 192.168.3.0 192.168.4.0 Routing Information Sources: Gateway Distance Last Update 192.168.2.1 120 00:00:13 192.168.4.1 120 00:00:22 Distance: (default is 120) Display the routing table on R2. R2# show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP + - replicated route, % - next hop override Gateway of last resort is not set R 192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:20, Serial0/0/0 192.168.2.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.2.0/24 is directly connected, Serial0/0/0 L 192.168.2.2/32 is directly connected, Serial0/0/0 192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.3.0/24 is directly connected, GigabitEthernet0/0 L 192.168.3.1/32 is directly connected, GigabitEthernet0/0 192.168.4.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.4.0/24 is directly connected, Serial0/0/1 L 192.168.4.2/32 is directly connected, Serial0/0/1 R 192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:01, Serial0/0/1 R2# You are now logged into R3. Verify the networks being advertised in RIP on router R3. R3# show ip protocols Routing Protocol is "rip" Sending updates every 30 seconds, next due in 10 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: rip Default version control: send version 1, receive any version Interface Send Recv Triggered RIP Key-chain GigabitEthernet0/0 1 2 1 Serial0/0/1 1 2 1 Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 192.168.4.0 192.168.5.0 Passive Interface(s): Routing Information Sources: Gateway Distance Last Update 192.168.4.2 120 00:00:14 Distance: (default is 120) Display the routing table on R3. R3# show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP + - replicated route, % - next hop override Gateway of last resort is not set R 192.168.1.0/24 [120/2] via 192.168.4.2, 00:00:02, Serial0/0/1 R 192.168.2.0/24 [120/1] via 192.168.4.2, 00:00:02, Serial0/0/1 R 192.168.3.0/24 [120/1] via 192.168.4.2, 00:00:02, Serial0/0/1 192.168.4.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.4.0/24 is directly connected, Serial0/0/1 L 192.168.4.1/32 is directly connected, Serial0/0/1 192.168.5.0/24 is variably subnetted, 2 subnets, 2 masks C 192.168.5.0/24 is directly connected, GigabitEthernet0/0 L 192.168.5.1/32 is directly connected, GigabitEthernet0/0 R3# You successfully verified RIP settings and routes on R2 and R3.

OSPFv3

Version 3 of the OSPF routing protocol. It is used to support both IPv4 and IPv6 unicast address families.

Best Route = Longest Match

What is meant by the router must find the best match in the routing table? Best match is equal to the longest match. For there to be a match between the destination IPv4 address of a packet and a route in the routing table, a minimum number of far left bits must match between the IPv4 address of the packet and the route in the routing table. The subnet mask of the route in the routing table is used to determine the minimum number of far left bits that must match. Remember that an IPv4 packet only contains the IPv4 address and not the subnet mask. The best match is the route in the routing table that has the most number of far left matching bits with the destination IPv4 address of the packet. The route with the greatest number of equivalent far left bits, or the longest match, is always the preferred route. In the figure, a packet is destined for 172.16.0.10. The router has three possible routes that match this packet: 172.16.0.0/12, 172.16.0.0/18, and 172.16.0.0/26. Of the three routes, 172.16.0.0/26 has the longest match and is chosen to forward the packet. Remember, for any of these routes to be considered a match there must be at least the number of matching bits indicated by the subnet mask of the route.

Level 2 child route

a route with a subnet mask greater than the classful mask of the network address

Remote IPv6 Network Entries

a routing table entry on R1 for the route to remote network 2001:DB8:CAFE:3::/64 on R3. The entry identifies the following information: Route source - Identifies how the route was learned. Common codes include O (OSPF), D (EIGRP), R (RIP), and S (Static route). Destination network - Identifies the address of the remote IPv6 network. Administrative distance - Identifies how trustworthiness of the route source. IPv6 uses the same distances as IPv4. Metric - Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. Next hop - Identifies the IPv6 address of the next router to forward the packet to. Outgoing interface - Identifies the exit interface to use to forward a packet toward the final destination. When an IPv6 packet arrives on a router interface, the router examines the IPv6 header and identifies the destination IPv6 address. The router then proceeds through the following router lookup process. The router examines level 1 network routes for the best match with the destination address of the IPv6 packet. Just like IPv4, the longest match is the best match. For example, if there are multiple matches in the routing table, the router chooses the route with the longest match. A match is made by matching the far left bits of the packet's destination IPv6 address with the IPv6 prefix and prefix-length in the IPv6 routing table.

Directly Connected Entries

directly connected route entries display the following information: Route source - Identifies how the route was learned. Directly connected interfaces have two route source codes (C identifies a directly connected network while L identifies that this is a local route.) Directly connected network - The IPv6 address of the directly connected network. Administrative distance - Identifies the trustworthiness of the route source. IPv6 uses the same distances as IPv4. A value of 0 indicates the best, most trustworthy source. Metric - Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. Outgoing interface - Identifies the exit interface to use when forwarding packets to the destination network.

Route Lookup Process

network routes for the best match with the destination address of the IPv4 packet: 1. If the best match is a level 1 ultimate route, then this route is used to forward the packet. 2. If the best match is a level 1 parent route, proceed to the next step. In Figure 2, the router examines child routes (the subnet routes) of the parent route for a best match: 3. If there is a match with a level 2 child route, that subnet is used to forward the packet. 4. If there is not a match with any of the level 2 child routes, proceed to the next step. In Figure 3, the router continues searching level 1 supernet routes in the routing table for a match, including the default route, if there is one: 5. If there is now a lesser match with a level 1 supernet or default routes, the router uses that route to forward the packet. 6. If there is not a match with any route in the routing table, the router drops the packet. Note: A route referencing only a next-hop IP address and not an exit interface, must be resolved to a route with an exit interface, if Cisco Express Forwarding (CEF) is not being used. Without CEF, a recursive lookup is performed on the next-hop IP address until the route is resolved to an exit interface. CEF is enabled by default.

Dynamic Routing Protocol Components

outing protocols are used to facilitate the exchange of routing information between routers. A routing protocol is a set of processes, algorithms, and messages that are used to exchange routing information and populate the routing table with the routing protocol's choice of best paths. The purpose of dynamic routing protocols includes: Discovery of remote networks Maintaining up-to-date routing information Choosing the best path to destination networks Ability to find a new best path if the current path is no longer available The main components of dynamic routing protocols include: Data structures - Routing protocols typically use tables or databases for its operations. This information is kept in RAM. Routing protocol messages - Routing protocols use various types of messages to discover neighboring routers, exchange routing information, and other tasks to learn and maintain accurate information about the network. Algorithm - An algorithm is a finite list of steps used to accomplish a task. Routing protocols use algorithms for facilitating routing information and for best path determination. Routing protocols allow routers to dynamically share information about remote networks and automatically offer this information to their own routing tables. Click Play in the figure to see an animation of this process. Routing protocols determine the best path, or route, to each network. That route is then offered to the routing table. The route will be installed in the routing table is there is not another routing source with a lower administrative distance. For example, a static route with an administrative distance of 1 will have precedence over the same network learned by a dynamic routing protocol. A primary benefit of dynamic routing protocols is that routers exchange routing information when there is a topology change. This exchange allows routers to automatically learn about new networks and also to find alternate paths when there is a link failure to a current network.

Enable and Verify RIPv2

y default, when a RIP process is configured on a Cisco router, it is running RIPv1, as shown in Figure 1. However, even though the router only sends RIPv1 messages, it can interpret both RIPv1 and RIPv2 messages. A RIPv1 router ignores the RIPv2 fields in the route entry. Use the version 2 router configuration mode command to enable RIPv2, as shown in Figure 2. Notice how the show ip protocols command verifies that R2 is now configured to send and receive version 2 messages only. The RIP process now includes the subnet mask in all updates, making RIPv2 a classless routing protocol. Note: Configuring version 1 enables RIPv1 only, while configuring no version returns the router to the default setting of sending version 1 updates but listening for version 1 and version 2 updates.