Notice for network engineers: 30 classic Routing Problems (1)

As a network engineer, it is necessary to deal with vrouters frequently. In the face of all kinds of routing problems, no one can say that they can do anything. Today, we will gather together various Routing Problems, hoping to help you.

1. When to use the multi-route protocol? When two different routing protocols need to exchange routing information, they need to use multiple routing protocols. Of course, route redistribution can also exchange route information. In the following cases, you do not need to use the multi-route Protocol: upgrade from the old version of the Internal Gateway Protocol (I g p) to the new version of the I G P.

To use another routing protocol, you must retain the original one.

You want to terminate the internal route to avoid interference from other routers that do not strictly filter the monitoring function.

You are in an environment composed of routers from multiple manufacturers.

2. What is distance vector routing protocol? The distance vector routing protocol is designed for small network environments. In a large network environment, such protocols will generate large traffic when learning routes and maintaining routes, occupying excessive bandwidth. If the route selection table update is not received from the adjacent site within 9 0 seconds, the adjacent site is considered inaccessible. Every 30 seconds, the distance vector routing protocol sends the entire route selection table to the adjacent site to update the route selection table of the adjacent site. In this way, it can collect a list of networks from other sites (directly connected or connected in other ways) for route selection. Distance Vector Routing uses the number of hops as the metric value to calculate the number of routers that need to pass to the destination.

For example, r I p uses the B e l m a n-F o r d algorithm to determine the shortest path, that is, the line that can reach the destination as long as it passes through the smallest hop count. The maximum number of hops allowed is usually set to 1 5. Terminals that must pass through more than five vrouters are considered inaccessible.

Distance Vector routing protocols include ip rip, ipx rip, A p l e Talk rt m p, And I G R P.

3. What is the connection status routing protocol? The link status routing protocol is more suitable for large networks. However, due to its complexity, the router needs more c p u resources. It can detect broken links or new routers in a shorter period of time, so that the convergence time of the Protocol is shorter than that of the Distance Vector routing protocol. Generally, if you do not receive the he l lo packet from the neighboring station within one 0 second, it is deemed that the neighboring station is no longer reachable. A connection status router sends an update message to its neighbor to notify it of all the links it knows. It determines that the measurement value of the optimal path is a numerical cost, which is generally determined by the bandwidth of the link. Links with the minimum cost are considered optimal. In the Shortest Path priority algorithm, the maximum possible cost is almost unlimited.

If the network does not change, the router only needs to periodically refresh the route selection table that has not been updated (the duration of the cycle can be from 3 0 minutes to 2 hours ).

The connection status routing protocols include ip ospf, ipx nlsp, And I s-I S.

Can a vro use the distance vector routing protocol and the link status routing protocol? Yes. Each interface can be configured to use different routing protocols. However, they must be able to exchange routing information by allocating routes.

4. What is an access table? The access table is a series of rules that the manager adds to control data packets input and output in the vro. It is not generated by the router itself. The Access Table allows or disables data packets from entering or outputting to the destination. The table items for accessing the table are executed sequentially. When the data packet arrives, the system first checks whether it is restricted by the first table item. If not, it is executed sequentially; if it matches the first table item, you do not have to perform the following table item check whether it is allowed or disabled.

Each Protocol of each interface can have only one access table.

5. What types of access tables are supported? The number of an access table can be determined. The specific protocol and its corresponding access table number are as follows:

◎ I P standard Access Table No.: 1 ~ 9 9

◎ I P extended access table No.: 1 0 0 ~ 1 9 9

◎ I P X standard Access Table No.: 8 0 0 ~ 8 9 9

◎ I P X extended access table No.: 1 0 0 0 ~ 1 0 9 9

◎ AppleTa l k Access Table No.: 6 0 0 ~ 6 9 9

Note: In Cisco IOS Release11.2 or later versions, you can use the famous access table to determine the number between 1 and later ~ 199 access table.

6. How to create an IP standard access table?

The following command creates an I P standard Access table: access-list Access list number {permit | deny} source [source-mask]

In this command:

◎ Access list number: determines which access table the entry belongs. It is a number ranging from 1 to 9.

◎ Permit | deny: indicates whether the entry permits or blocks information traffic from a specific address.

◎ Source: determine the source I P address.

◎ S o u r c e-m a s k: determines which bits in the address are used for matching. If a bit is "1", it indicates that the bit in the address is unnecessary. If it is "0", it indicates that the bit in the address will be used for matching. Wildcard characters can be used.

The following is an example of an access table in the vro configuration file:

Router # show access-lists

Standard IP access list 1

Deny 204.59.144.0, wildcard bits 0.0.0.255

Ermit any

7. When will route redistribution be used? Route redistribution is usually configured on routers responsible for learning routes from one autonomous system and then broadcasting to another autonomous system. If you are using I g r p or e I G R P, route redistribution is generally automatically executed.

8. What is Management Distance? Management Distance refers to the route reliability of a routing protocol. Each routing protocol is assigned a level of trust from high to low reliability. This level of trust is called the Management Distance. For the routing information from two different routing protocols to one destination, the router first determines which Protocol to trust based on the Management Distance.