Routing Protocol RIP-2

RIP-2 Basic Concepts Routers using RIP-2 advertise a small amount of simple information about each subnet to their neighbors. Their neighbors in turn advertise the information to their neighbors, and so on, until all routers have learned the information

Example of How RIP-2 Advertises Routes

Interior and Exterior Routing Protocols IP routing protocols fall into one of two major categories: – Interior Gateway Protocol (IGP): A routing protocol that was designed and intended for use inside a single autonomous system – Exterior Gateway Protocol (EGP): A routing protocol that was designed and intended for use between different autonomous systems

Comparing Locations for Using IGPs and EGPs

Routing Protocol Classes/Algorithms and Protocols

Metrics Routing protocols must have some way to decide which route is best when a router learns of more than one route to reach a subnet. The lower the metric, the better the route. RIP uses a metric called hop count, which measures the number of routers (hops) between a router and a subnet. Maximum hops in RIP is 15

Classless and Classful Routing Protocols Some routing protocols must consider the Class A, B, or C network number that a subnet resides in when performing some of its tasks. Other routing protocols can ignore Class A, B, and C rules altogether.

Convergence The term convergence refers to the overall process that occurs with routing protocols when something changes in a network topology. When a link comes up or fails, or when a router fails or is first turned on, the possible routes in the internetwork change. The processes used by routing protocols to recognize the changes, to figure out the now-best routes to each subnet, and to change all the routers’ routing tables, is called convergence.

Interior IP Routing Protocols Compared

RIP-2 Configuration Step 1 Use the router rip configuration command to move into RIP configuration mode. Step 2 Use the version 2 RIP subcommand to tell the router to use RIP Version 2 exclusively. Step 3 Use one or more network net-number RIP subcommands to enable RIP on the correct interfaces. Step 4 (Optional) As needed, disable RIP on an interface using the passiveinterface type number RIP subcommand.

RIP-2 Configuration RIP-2 The router multicasts routing updates to a reserved IP multicast IP address,

RIP-2 Verification

show ip route

Administrative Distance

show ip protocols Command

RIP Debug Output

Loop Prevention Split horizon route advertisement Route poisoning Holddown timers Maximum Distance Triggered updates

OSPF

OSPF Protocols and Operation OSPF features can be broken into three major categories: – Neighbors, – Database exchange – Route calculation

OSPF Protocols and Operation OSPF routers first form a neighbor relationship that provides a foundation for all continuing OSPF communications

OSPF Protocols and Operation After routers become neighbors, they exchange the contents of their respective LSDBs through a process called database exchange

OSPF Protocols and Operation Finally, as soon as a router has topology information in its link-state database (LSDB), it uses the Dijkstra Shortest Path First (SPF) algorithm to calculate the now-best routes and add those to the IP routing table

Identifying OSPF Routers with a Router ID OSPF RIDs are 32-bit numbers written in dotted decimal, so using an IP address is a convenient way to find a default RID. Alternatively, the OSPF RID can be directly configured, as covered in the later section “Configuring the OSPF Router ID.” As soon as a router has chosen its OSPF RID and some interfaces come up, the router is ready to meet its OSPF neighbors

Link-State Hello Packets Routers A and B both send Hello messages onto the LAN. They continue to send Hellos based on their Hello Timer settings. Soon afterward, the two routers can begin exchanging topology information with each other. Then they run the Dijkstra algorithm to fill the routing table with the best routes.

Hello messages have the following The Hello message follows the IP packet header, with IP packet protocol type 89. Hello packets are sent to multicast IP address , a multicast IP address intended for all OSPF-speaking routers. OSPF routers listen for packets sent to IP multicast address , in part hoping to receive Hello packets and learn about new neighbors.

Potential Problems in Becoming a Neighbor Subnet mask used on the subnet Subnet number (as derived using the subnet mask and each router's interface IP address) Hello interval Dead interval OSPF area ID Must pass authentication checks (if used) Value of the stub area flag

OSPF Database Exchange Based on the OSPF interface type, the routers may or may not collectively elect a Designated Router (DR) and Backup Designated Router (BDR). For each pair of routers that need to become fully adjacent, mutually exchange the contents of their respective LSDBs When completed, the neighbors monitor for changes and periodically reflood LSAs while in the Full (fully adjacent) neighbor state

No DR on a Point-to-Point Link with a DR on the LAN

choose the DR based on the following criteria The router sending the Hello with the highest OSPF priority setting becomes the DR. If two or more routers tie with the highest priority setting, the router sending the Hello with the highest RID wins. It's not always the case, but typically the router with the second- highest priority becomes the BDR. A priority setting of 0 means that the router does not participate in the election and can never become the DR or BDR. The range of priority values that allow a router to be a candidate are 1 through 255. If a new, better candidate comes along after the DR and BDR have been elected, the new candidate does not preempt the existing DR and BDR.

Summary of Neighbor States

Single-Area OSPF

Two-Area OSPF

OSPF Design Terminology

OSPF Configuration Step 1 Enter OSPF configuration mode for a particular OSPF process using the router ospf process-id global command. Step 2 (Optional) Configure the OSPF router ID by – a. Configuring the router-id id-value router subcommand – b. Configuring an IP address on a loopback interface Step 3 Configure one or more network ip-address wildcard-mask area area-id router subcommands, with any matched interfaces being added to the listed area. Step 4 (Optional) Change the interface Hello and Dead intervals using the ip ospf hello-interval time and ip ospf dead-interval time interface subcommands.

OSPF Configuration Step 5 (Optional) Impact routing choices by tuning interface costs as follows: – a. Configure costs directly using the ip ospf cost value interface subcommand. – b. Change interface bandwidths using the bandwidth value interface subcommand. – c. Change the numerator in the formula to calculate the cost based on the interface bandwidth using the auto-cost reference- bandwidth value router subcommand

OSPF Configuration Step 6 (Optional) Configure OSPF authentication: – a. On a per-interface basis using the ip ospf authentication interface subcommand – b. For all interfaces in an area using the area authentication router subcommand Step 7 (Optional) Configure support for multiple equal-cost routes using the maximum-paths number router subcommand.

OSPF Single-Area Configuration

Configuring the OSPF Router ID 1.If the router-id rid OSPF subcommand is configured, this value is used as the RID 2.If any loopback interfaces have an IP address configured and the interface has an interface status of up, the router picks the highest numeric IP address among these loopback interfaces. 3.The router picks the highest numeric IP address from all other interfaces whoseinterface status code (first status code) is up. (In other words, an interface is up/down state will be included by OSPF when choosing its router ID.)

Displaying OSPF-Related Information

Displaying the Hello and Dead Timers

IOS chooses an interface's cost based on the following rules 1. The cost can be explicitly set using the ip ospf cost x interface subcommand to a value between 1 and 65,535, inclusive. 2. IOS can calculate a value based on the generic formula Ref-BW / Int-BW, where Ref- BW is a reference bandwidth that defaults to 100 Mbps, and Int-BW is the interface's bandwidth setting. 3. The reference bandwidth can be configured from its default setting of 100 (100 Mbps) using the router OSPF subcommand auto-cost reference-bandwidth ref-bw, which in turn affects the calculation of the default interface cost.

EIGRP

EIGRP Concepts and Operation 1. Neighbor discovery: EIGRP routers send Hello messages to discover potential neighboring EIGRP routers and perform basic parameter checks to determine which routers should become neighbors. 2. Topology exchange: Neighbors exchange full topology updates when the neighbor relationship comes up, and then only partial updates as needed based on changes to the network topology. 3. Choosing routes: Each router analyzes its respective EIGRP topology tables, choosing the lowest-metric route to reach each subnet.

EIGRP Neighbors An EIGRP neighbor is another EIGRP-speaking router, connected to a common subnet, with which the router is willing to exchange EIGRP topology information. EIGRP uses EIGRP Hello messages, sent to multicast IP address , to dynamically discover potential neighbors. A router learns of potential neighbors by receiving a Hello

EIGRP Neighbors Then the router checks the following settings to determine if the router should be allowed to be a neighbor: It must pass the authentication process. It must use the same configured AS number. The source IP address used by the neighbor’s Hello must be in the same subnet.

Full and Partial EIGRP Updates

EIGRP Routing When a router learns multiple routes to the same subnet, it puts the best route in the IP routing table (successor route) EIGRP runs a simple algorithm to identify which routes could be used, keeping these loop-free backup routes in its topology table and using them if the currently best route fails. These alternative, immediately usable routes are called feasible successor routes

The Query and Reply Process When a route fails and has no feasible successor, EIGRP uses a distributed algorithm called Diffusing Update Algorithm (DUAL). DUAL sends queries looking for a loop-free route to the subnet in question The EIGRP DUAL process simply uses messages to confirm that a route exists, and would not create a loop, before deciding to replace a failed route with an alternative route.

EIGRP Summary and Comparisons with OSPF

EIGRP Configuration Step 1 Enter EIGRP configuration mode and define the EIGRP ASN by using the router eigrp as-number global command. Step 2 Configure one or more network ip- address [wildcard-mask] router subcommands. This enables EIGRP on any matched interface and causes EIGRP to advertise the connected subnet.

EIGRP Configuration Step 3 (Optional) Change the interface Hello and hold timers using the ip hellointerval eigrp asn time and ip hold-time eigrp asn time interface subcommands. Step 4 (Optional) Impact metric calculations by tuning bandwidth and delay using the bandwidth value and delay value interface subcommands.

EIGRP Configuration Step 5 (Optional) Configure EIGRP authentication. Step 6 (Optional) Configure support for multiple equal-cost routes using the maximum-paths number and variance multiplier router subcommands.

Basic EIGRP Configuration

Using Wildcard Masks with EIGRP