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This article mainly explains "what routing knowledge points web operators need to master". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what routing knowledge points web operators need to master".

Routing protocol (English: Routing protocol) is a network protocol that specifies the way packets are forwarded. The main node device of the Internet network is the router, which forwards the received data through the routing table. Forwarding policies can be manually specified (through static routes, policy routing, and so on).

1. When do I use the multirouting protocol?

When two different routing protocols want to exchange routing information, multirouting protocols are used. Of course, route redistribution can also exchange routing information.

You do not need to use a multirouting protocol in the following situations:

Upgrade from the old version of Interior Gateway Protocol (Interior Gateway Protocol,IGP) to the new version of IGP.

You want to use another routing protocol but you have to keep the original protocol.

Want to terminate the internal route so as not to be disturbed by other routers that do not have strict filtering supervision.

In an environment made up of routers from multiple manufacturers.

two。 What is a distance vector routing protocol?

Distance vector routing protocols are designed for small network environments. In a large network environment, this kind of protocol will generate a large amount of traffic and occupy too much bandwidth in learning and maintaining routing. If it does not receive an update to the routing table sent by the neighboring site within 90 seconds, it considers the neighboring site unreachable.

Every 30 seconds, the distance vector routing protocol sends the entire routing table to the neighboring sites, so that the routing tables of the neighboring sites are updated. In this way, it can collect a list of networks from other sites (directly connected or otherwise connected) for routing. The distance vector routing protocol uses hops as a metric to calculate the number of routers to reach the destination.

For example, R I P uses the B e l l m a n-F o r d algorithm to determine the shortest path, that is, the route that can reach the destination with the minimum number of hops. The maximum number of hops allowed is usually set at 1 / 5. Terminals that must pass through more than 15 routers are considered unreachable.

There are several distance vector routing protocols:

IP RIP, IPX RIP, Apple Talk RTMP and IGRP.

3. What is a link state routing protocol?

Link-state routing protocol is more suitable for large networks, but because of its complexity, routers need more CPU resources. It can find broken links or newly connected routers in a shorter time, so that the convergence time of the protocol is shorter than that of distance vector routing protocols.

Usually, if the hello message of the neighboring station is not received within 10 seconds, it thinks that the neighboring station is unreachable. A link-state router sends update messages to its neighboring stations, notifying it of all links it knows.

It determines that the metric of the optimal path is a numerical cost, which is generally determined by the bandwidth of the link. The link with the lowest cost is considered to be optimal. In the shortest path first algorithm, the value of the maximum possible cost can be almost infinite.

If there is no change in the network, the router can periodically refresh the unupdated routing table (the cycle can range from 30 minutes to 2 hours).

There are several link state routing protocols: IP OSPF, IPX NLSP, and IS-IS.

Can a router use both the distance vector routing protocol and the link state routing protocol?

Sure. Each interface can be configured to use a different routing protocol; however, they must be able to exchange routing information through redistribution of routes. (redistribution of routes will be discussed later in this chapter.)

4. What is an access table?

The access table is a series of rules that managers join to control the input and output of packets in the router. It is not generated by the router itself. The access table allows or forbids packets to enter or output to the destination.

The table items of the access table are executed sequentially, that is, when the packet arrives, first see whether it is constrained by the first table item, and then execute it down sequentially; if it matches the first table item, it is no longer necessary to check the following table items, whether allowed or prohibited.

There can be only one access table for each protocol per interface.

What types of access tables are supported?

An access table can be determined by its number. The specific protocol and its corresponding access table numbers are as follows:

IP Standard access Table No.: 1-9-9

IP extended access Table No.: 1 00 9 9

IPX Standard access Table No.: 8 00 8 9 9

IPX extended access Table No.: 1 0 0 9 9

AppleTalk access Table No.: 6 00006 9 9

Tip: in Cisco IOS Release11.2 or above, you can use the named access table to determine the access table numbered 1: 199.

5. How do I create an IP standard access table?

The creation of an IP standard access table can be accomplished by the following command:

Access-list access list number {permit | deny} source [source-mask]

In this command:

Access list number: determine which access table this entry belongs to. It is a number from 1 to 9 9.

Permit | deny: indicates whether this entry allows or blocks traffic from a specific address.

Source: determine the source IP address.

S o u r c e-m a s k: determine which bits in the address are used to match. If a bit is "1", it means that the bit in the address is ignored, and if it is "0", it indicates that the bit in the address will be used to match. You can use wildcards.

The following is an example of an access table in a router configuration file:

Router# show access-lists Standard IP access list 1 deny 204.59.144.0, wildcard bits 0.0.0.255 ermit any

6. When is route redistribution used?

Route redistribution is usually configured on routers that are responsible for learning routes from one autonomous system and then broadcasting to another. If you are using IGRP or EIGRP, route redistribution is usually performed automatically.

7. What is administrative distance?

Administrative distance refers to the routing credibility of a routing protocol. Each routing protocol assigns a trust level according to its reliability from high to low, which is called administrative distance. For the routing information from two different routing protocols to a destination, the router first decides which protocol to trust according to the administrative distance.

8. Why is it important to identify adjacent routers?

Identifying adjacent routers in a small network is not a major problem. Because when one router fails, other routers can converge within an acceptable time. However, in large networks, the delay of finding a faulty router may be very large.

Knowing that neighboring routers can accelerate convergence, because routers can know faulty routers more quickly, because the interval between hello messages is shorter than the interval between routers exchanging information.

A router using a distance vector routing protocol will not find that the neighboring router is unreachable until the neighboring router does not send routing update information, which usually takes 10-90 seconds. On the other hand, routers using link-state routing protocols can find that neighboring routers are unreachable without receiving the hello message, which is usually 10 seconds.

How do distance vector routing protocols and link state routing protocols discover neighboring routers?

A router that uses a distance vector routing protocol creates a routing table (including networks directly connected to it), and it sends the routing table to the router that is directly connected to it.

A neighboring router merges the routing table it receives into its own routing table, and it also sends its own routing table to its neighboring routers. Routers that use link-state routing protocols create a link state table that includes a list of destinations for the entire network. In the update message, each router sends its entire list.

When a neighboring router receives this update message, it copies its contents and sends the information to its neighboring stations. There is no need to recalculate when forwarding the contents of the routing table.

Note that routers using IGRP and EIGRP broadcast hello messages to discover neighboring stations and exchange routing updates like OSPF. EIGRP maintains a table of neighboring stations for each network layer protocol, which includes the address of the neighboring station, the number of messages waiting to be sent in the queue, the average time it takes to receive or send a message from the neighboring station, and the time that no message is received from the neighboring station before determining that the link is broken.

9. What is an autonomous system?

An autonomous system is a group of routers and networks under the control of a management organization. It can be a router directly connected to a LAN, but also connected to an Internet; it can be a number of Lans interconnected by an enterprise backbone.

All routers in an autonomous system must be connected to each other, run the same routing protocol, and assign the same autonomous system number. Links between autonomous systems use an external routing protocol, such as BGP.

10. What is BGP?

BGP (Border GatewayProtocol) is a routing protocol that dynamically exchanges routing information between autonomous systems. The classic definition of an autonomous system is a group of routers under the control of a management organization that uses IGP and normal metrics to forward messages to other autonomous systems.

The term autonomous system is used in BGP to emphasize the fact that the management of an autonomous system provides a unified internal routing plan for other autonomous systems, which provides a consistent description of the networks that can be reached through it.

11. What types of sessions are supported by BGP?

The session between BGP neighboring routers is based on the TCP protocol. The TCP protocol provides a reliable transport mechanism that supports two types of sessions:

External BGP (EBGP): a session between routers belonging to two different autonomous systems. These routers are adjacent and share the same media and subnets.

Internal BGP (IBGP): a session between routers within an autonomous system. It is used to coordinate and synchronize the routing process within the autonomous system.

BGP routers can be separated by several routers anywhere or even in the middle of an autonomous system. Note that the content of the initial data flow is the entire BGP routing table. However, when the routing table changes later, the router only transmits the changed part. BGP does not need to update the entire routing table periodically.

Therefore, during the period when a connection is established, an BGP sender must keep the entire BGP routing table common to all current peer routers. The BGP router periodically sends Keep Alive messages to confirm that the connection is active. When an error or special situation occurs, the router sends a Notification message. When an error occurs on a connection, a notification message is generated and the connection is disconnected.

12. Does BGP allow route redistribution?

Allow it. Because BGP is mainly used for routing between autonomous systems, it must support the synthesis of routing tables for RIP, OSPF, and IGRP in order to transfer their routing tables to an autonomous system.

BGP is an external routing protocol, so it operates differently from an internal routing protocol. In BGP, you can use the NETWORK command to create a route in the IP routing table only if a route already exists in the BGP routing table.

Thank you for your reading. The above is the content of "what routing knowledge points need to be mastered by web operation and maintenance". After the study of this article, I believe you have a deeper understanding of what routing knowledge points web operation and maintenance need to master, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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