Dynamic routing protocol

Dynamic routing protocol

n Dynamic routing protocol Basics

1. Dynamic Routing Overview

Dynamic routing is the process by which routers communicate with each other, transmit routing information, and update routing tables with received routing information. It can adapt to the changes of network structure in real time. If the routing update information indicates that the network has changed, the routing software will recalculate the route and issue a new routing update information. This information, through each network, causes the routers to restart their routing algorithms and update their respective routing tables to dynamically reflect the changes in the network topology.

If the dynamic routing protocol is used, the router sends its own routing information to neighboring routers and receives routing information from neighboring routers, optionally saving these routing information and generating its own routing table.

Dynamic routing is suitable for networks with large network size and complex network topology. the features of dynamic routing are as follows:

? management tasks are reduced. because the process of dynamic routing is completely done by the router itself, the administrator only needs to do a simple configuration, routing learning, Routing and Routing and maintenance of the task is done by dynamic routing. With dynamic routing configured, when the network topology changes, there is no need for reconfiguration, and dynamic routing understands these changes to modify the routing table.

? consumes the bandwidth of the network. because dynamic routing communicates with other routers to understand the network, each router tells the other routers what they know about the network, and learns the network information they do not know from other routers, which inevitably sends packets that consume a certain amount of network traffic.

2. Dynamic routing protocol

1) Overview of dynamic routing Protocols

Dynamic routing is based on some kind of routing protocol (Routing Protocol). The routing protocol defines some rules for routers to communicate with other routers. In other words, the routing protocol specifies how routers learn to route, what criteria are used to select routes, and how to maintain the path by information.

The dynamic routing protocol is like the language used to communicate information between routers, through which network connection information and status information can be shared between routers. Dynamic routing protocol is not limited to path selection and routing table update, when the optimal path to the destination network occurs, the dynamic routing protocol can be substituted by selecting the next optimal path in the remaining available paths.

Each dynamic routing protocol has its own routing algorithm, and the algorithm is a series of steps to solve the problem. A routing algorithm must have at least the following necessary steps:

(1) Passing routing information to other routers.

(2) Receive routing information from other routers.

(3) The optimal path of each destination network is computed based on the received routing information, and the routing table is generated.

(4) According to the network topology changes in time to respond, adjust the route to generate a new routing table, while the topology changes in the form of routing information to other routing information.

2) measure value

Different routing protocols use different metrics, and sometimes multiple measures are used.

? Hops : hop count metric can simply record the hop count of the router.

? Bandwidth: The bandwidth (Bandwidth) metric will select a high-bandwidth path rather than a low-bandwidth path.

? load: The load measure reflects the amount of traffic that is taking up the link along the way. The optimal path should be the least loaded path. Unlike hop count and bandwidth, the load on the path changes, and so the metrics change accordingly. It is important to note that routing swings (frequent changes in optimal paths) can occur frequently if metrics change too frequently. The routing swing negatively affects the router's CPU, the bandwidth of the data link, and the stability of the entire network.

? delay: delay (delay) measures the time it takes for a packet to pass through a path. The route selection protocol using the delay as a measure will choose the path with the lowest delay as the optimal path.

? reliability: The Reliability (reliability) metric is used to measure the likelihood of a link failure in some situation. Reliability can be variable or fixed. The number of times a link has failed or the number of times an error has been received within a specific time interval is an example of a variable reliability metric. A fixed reliability metric is a known amount based on a link determined by the administrator. The path with the highest reliability is the preferred choice.

? Cost: The cost is a generic term used to describe the merits of a route, the minimum cost (highest cost) or the shortest (longest) refers only to the way the routing protocol is based on its own particular metric. The network administrator can define the cost manually.

3) Convergence

The dynamic routing protocol must contain a series of procedures that are used by routers to advertise local direct-attached networks to other routers, receive and process similar information from other routers, and relay information received from other routers. In addition, the routing protocol needs to define measures that determine the optimal path. Another standard for routing protocols is that the accessible information in all routers on the Internet network must be consistent. The process of making all routing tables conform is called Convergence (Convergence). Convergence time is the sum of the total network sharing of information and the time it takes for all routers to calculate the optimal path.

3. static Routing and dynamic routing

Through the learning of dynamic routing, it feels that dynamic routing protocol is better than static routing protocol. The dynamic routing protocol is automatic detection and updates the routing table with the transformation of the network topology. Static routing protocols are difficult to manage for large and medium-sized networks, but it is convenient to configure static routes in small networks.

Both static and dynamic routes have their own characteristics and practical scope, and static routes and dynamic routes complement each other in the network. In all routes, static routes except for direct-attached routes have the highest precedence. When a packet is selected in the router, the router looks for the static route first, and if it finds the forwarding packet according to the corresponding static route, then finds the dynamic route. static routes prevail when static routes collide with dynamic routes.

n Dynamic routing Protocol classification

The common routing protocol can be divided into distance vector routing protocol and link state routing protocol. The distance vector routing protocol chooses routes based on the number of routers that pass from the source network to the target network, typical protocols such as RIP and IGRP. The link state routing protocol takes into account the various paths from the source network to the target network to select routes, typical protocols such as OSPF and Is-is.

1. Distance Vector routing protocol

The distance vector name is derived from the fact that the route is advertised in vectors (distance, direction), where the distance is defined by the metric and the direction is defined by the next hop router. For example, the direction of the next-hop router X can reach target a, which is 5 hops away, which implies that each router learns the routing information they observe from the neighboring router, and then advertises its observed routing information outward. Because each router relies on neighboring routers for information, and neighboring routers learn routes from their neighboring routers, the distance vector routing is sometimes considered "routing based on rumors".

2. link State Routing protocol

The information used by the distance vector routing protocol can be likened to the information provided by the Signpost, while the link state routing protocol is like a road map. A link-state router is a routing decision that is not easy to spoof and makes a mistake because it has a complete network diagram. The link state differs from the way in which the distance vectors are routed according to rumors, because the link state router obtains firsthand information from the peer router. Each router generates some information about itself, the local direct-attached network, and the status of those links. This information is transferred from one router to another, and each router makes a backup copy of the information, but never changes the information. The ultimate goal is that each router has an identical information about the internetwork, and each router can independently compute the optimal path for each destination.

How n RIP Routing protocol Works

? Regular updates (periodic updates): regular updates mean that updates will be sent every time a specific period passes. It is important to note that if the update information is sent too frequently it may cause congestion, but if the update information is sent infrequently, the network convergence time may be unacceptably long.

? neighbor (Neighbors): in the router's view, a neighbor usually means a router that shares the same data link. The distance vector routing protocol sends update information to the neighbor router and relies on the neighbor to pass the update information to its neighbors. As a result, the distance vector routing protocol is said to be using hop-hopping update mode.

? Broadcast update (broadcast update): How does the router look for other routers when the router is first activated on the network? And how does it announce its existence? The simplest method is to send the update information to the broadcast address (the broadcast address is 255.255.255.255 in the IP network). Neighbor routers that use the same router selection protocol will receive broadcast packets and take corresponding actions. Hosts and other devices that do not care about routing update information discard the packet.

? full Routing Table update: Most distance vector routing protocols use a very simple method to tell a neighbor what it knows, and this method is to broadcast its entire routing table. After the neighbors receive these updates, they collect the information they need and others are discarded.

1. formation of routing tables

When the IP address of the interface is configured for the router, and in the case of an interface up, a direct-attached route entry appears in the routing table for each router. If the router is configured with RIP routing protocols, the routers will send their own routing table information to each other.

The router receives the routing information sent by the neighboring router, compares it to the entry in its own routing table, and if this routing information is already present in the routing table, the router compares whether the newly received routing information takes precedence over the existing entry. If the existing entry is preferred, the router replaces the original route entry with the new routing information. Conversely, the router compares whether the route information is from the same source as the original entry, and if it is from the same source, it is updated, otherwise the routing information is ignored.

2. RIP metrics and update time

1) RIP The measure value

The RIP routing protocol uses hop count as the only measure.

The maximum number of hops specified in RIP is 15, and 16 hops is considered unreachable. Therefore, the RIP routing protocol does not work with large WANs.

2) RIP The update time

RIP uses UDP protocol, port number is 520

After the router starts, the average of every 30s on the interface from each start RIP protocol constantly sends the way out by updating the message.

3. horizontal split (split Horizon)

After the network converges, the router still sends out the entire routing table at a 30s interval.

Performing a horizontal split can prevent routing loops from occurring, and the rules for horizontal partitioning are: Learning from an interface to routing information, and no longer sending it out from this interface. Horizontal segmentation can not only prevent the generation of routing loops, but also reduce the link bandwidth resources occupied by routing update information.

Configuration and validation of n-RIP routing protocol

1. Configure Commands

Configure the RIP routing protocol to start the RIP process on the router first.

The command to start the RIP process is as follows:

Router (config) # Router RIP

Router (Config-router) #

The main network number of all the interfaces on the router that initiates the RIP is then declared with the following command:

Router (config-router) # network network-number

2. Verify the configured commands

? View the routing table

Use the View route table command to see if the routing table learned the correct routing entry through the RIP protocol, with the following command:

router# show ip route

In the routing table, you can see all of the network segments in the networks, indicating that RIP is configured correctly. In the routing entry preceded by a direct-connect route labeled C, Mark R for the route learned through the RIP routing protocol. The [120/1] after the segment number represents the administrative distance (priority) and measure (hop count).

The administrative distance is a priority measure, and when both routes reach the same network, the router chooses a route with a smaller administrative distance to reach the target network segment. Static routes have an administrative distance of 1, and the RIP protocol has an administrative distance of 120, so if you reach the same network segment and configure both static routes and RIP, the router chooses the path to which the static route points to forward the data.

RIP Priority : 120,OSPF Priority:

? to view the configuration of a routing protocol

Using the command to view the routing protocol configuration, you can view information about the RIP timer, the version used, the network segment being declared, and the following commands:

router# show IP Protocols

By default, RIP uses version 1 to send routing updates and can accept updates for routes of V1 and v2 two versions.

n RIP v1 and Tip v2

RIP routing protocol contains two versions, RIP v1 and RIP v2. The main differences between version 1 and version 2 are as follows:

? RIP v1 broadcasts send routing updates, broadcast addresses for 255.255.255.255;rip v2 group advertisements send routing updates, multicast address is 224.0.0.9

? RIP V1 is a class-routing (classful) protocol that does not carry a netmask when declaring routing information, whereas RIP v2 is a class-free routing (classless) protocol that carries a netmask when declaring routing information.

Another feature of the class routing protocol is the automatic routing summarization on the border routers.

N RIP v2 Configuration

To configure the RIP protocol, use the version v2 command as follows:

Router (config) # Router RIP

Router (config-router) # version 2

RIP v2 routes are aggregated on the primary network boundary by default, so you need to turn off the route summarization feature.

Router (config-router) # no Auto-summary

The main network number is then declared.

Router (config-router) # network network-number

n verifying RIP v1 and RIP v2

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Lab Environment:

The topology map is connected to the network, where 10.1.1.0/24 and 10.1.2.0/24 use the loopback interface respectively.

Requirements Description:

Requires that RIP v1 and RIP v2 be configured separately, and verify that the network can communicate properly.

Specific steps:

1. Configure the router's interface address to enable router interoperability

2. Configure the RIP v1 protocol, use show IP route to view the routing table, pingR1 or R3 loopback interface address on R2, verify that network traffic is normal.

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3. Configure the RIP v2 protocol, use the ping, show ip route view command to verify that network traffic is normal.

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n RIP configuration

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Lab Environment:

According to the topology map to connect the network, through the configuration of routers to achieve the company's internal network interoperability, the specific planning situation is as follows.

? R1 and R2 's connected address: 192.168.0.0/24,r1 and R3 's connected address: 192.168.1.0/24,R2 and R3 's connected address: 192.168.2.0/24,r3 and R4 's connected address: 192.168.3.0/24.

? use the loopback interface of the router to simulate the client hosts inside the company, R1 LOOPBACK0:192.168.10.0/24,R2 loopback0:192.168.20.0/24,r2 Loopback0 : 192.168.30.0/24,r4 's loopback0:192.168.40.0/24.

Requirements Description:

To avoid frequent configuration due to changes in the network segment, the RIP router protocol is required.

Specific steps:

1. Configure the router's interface address to enable router interoperability.

2. Configure RIP protocol to achieve network interoperability.

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4. to view the routing table using the show ip route command

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5. Use the ping command to verify that the network and RIP protocols are normal

650) this.width=650; "Style=" background-image:none;border-bottom:0px;border-left:0px;margin:0px; padding-left:0px;padding-right:0px;border-top:0px;border-right:0px;padding-top:0px; "Title=" clip_image045 " Border= "0" alt= "clip_image045" src= "Http://s3.51cto.com/wyfs02/M02/77/91/wKiom1ZpiaOQqa2CAAAUCISv4ww005.png" height= "Notoginseng"/>650) this.width=650; "Style=" background-image:none;border-bottom:0px;border-left:0px;margin:0px; padding-left:0px;padding-right:0px;border-top:0px;border-right:0px;padding-top:0px; "Title=" clip_image046 " Border= "0" alt= "clip_image046" src= "Http://s3.51cto.com/wyfs02/M00/77/91/wKiom1ZpiaPRdwWoAAAUgc4Uljs155.png" height= "/>650" this.width=650; "style=" background-image:none;border-bottom:0px;border-left:0px; padding-left:0px;padding-right:0px;border-top:0px;border-right:0px;padding-top:0px; "Title=" clip_image047 " Border= "0" alt= "clip_image047" src= "Http://s3.51cto.com/wyfs02/M01/77/91/wKiom1ZpiaSySTz1AAAUUbeNhl4124.png" height= "Notoginseng"/>

Dynamic routing Protocol