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Technical terms that must be understood by network engineers

Router problem:

1. When to 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 the Interior Gateway Protocol (Interior Gateway Protocol,I G P) to the new version of I G P.

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

You want to terminate internal routing so as not to be disturbed by other routers that do not have strict filtering and regulatory capabilities.

You are in an environment made up of routers from multiple manufacturers.

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, A p p l e Talk RT M P and I G R P.

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 C P U 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 H E L LO 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. )

2. What is the 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:

◎ I P Standard access Table No.: 1 # 9 9

◎ I P extended access Table No.: 100 million 1 9 9

◎ I P X Standard access Table No.: 8 00 8 9 9

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

◎ AppleTa l k 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 with the number 1: 199.

How do I create an IP standard access table?

The creation of an I / P 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

Permit any

3. When will route redistribution be 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 I G R P or E I G R P, route redistribution is usually performed automatically.

4. 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.

6. How to configure redistribution?

Before redistributing routes, you must first:

1) decide where to add the new agreement.

2) determine the autonomous system boundary router (ASBR).

3) decide which protocol is at the core and which is at the border.

4) determine the direction of route redistribution.

You can use the following command to reassign routing updates (this example is for OSPF):

Router (config-router) # redistribute protocol [process-id] [metric metric- value] [metric-type type-value] [subnets]

In this command:

◎ protocol: the source routing protocol that indicates the route redistribution of the router.

The main values are: bgp, eqp, igrp, isis, ospf, static [ip], connected, and rip.

◎ process-id: indicates the process ID of the OSPF.

◎ metric: is an optional parameter that indicates the metric of the redistributed route. The default measure is 0.

7. 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.

8. 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 B G P.

9. 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.

10. What kinds 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:

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

O Internal BGP (IBGP): is 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 in a connection, a notification message is generated and the connection is disconnected. " -from RFC11654 and BGP operations.

11. 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.

12. How do I display all BGP routes in the database?

To display all BGP routes in the database, simply enter at the EXEC command line:

Show ip bgp paths

The output of this command might be:

Address Hash Refcount MetricPath

0 x 2 9 7 A 9 C 0 2 0 i

13. What is split horizon?

Split horizon is a technology that avoids the emergence of routing rings and speeds up route aggregation. Because the router may receive its own routing information, which is useless, split horizon does not reverse advertise any routing updates received from the terminal, but only advertises those routes that will not be cleared by counting to infinity.

14. How is the routing ring generated?

Due to the existence of the route aggregation time of the network, the new or changed routes in the routing table can not be quickly stable in the whole network, resulting in the existence of inconsistent routes, resulting in routing rings.

15. What is a measure?

The measure represents the distance. They are used to determine the optimal route when looking for a route. When each routing algorithm generates a routing table, it generates a value (measure) for each path through the network, and the minimum value represents the optimal path. The calculation of metrics can take into account only one characteristic of the path, but the more complex metrics are generated by combining multiple characteristics of the path. Some commonly used metrics are:

Number of ◎ hops: the number of router output ports through which the message is to be passed.

◎ Ticks: the delay of the data link (approximately 1 pound 18 per second).

◎ cost: can be an arbitrary value based on bandwidth, cost, or other calculation methods defined by network managers.

◎ bandwidth: capacity of the data link.

◎ delay: the time it takes for a message to travel from the source to the destination.

◎ load: the size of the portion of a network resource or link that has been used.

◎ reliability: the rate of error bits in a network link.

◎ maximum transmission unit (MTU): the maximum message length (in bytes) acceptable to all links on a path.

What type of routing metric does IGRP use? What does this measure consist of?

IGRP uses multiple routing metrics. It includes the following parts:

◎ bandwidth: the smallest bandwidth from source to destination.

◎ delay: the interface delay accumulated in the path.

◎ reliability: the worst possible reliability from source to destination, based on the state of link retention.

◎ load: the worst-case load on a source-to-destination link, expressed in bits per second.

◎ MTU: the lowest MT U value in the path.

16. Can the measurement be modified or adjusted?

Add a positive offset. The complete structure of this command is as follows: you can use the OFFSET-LIST root subcommand

Add a positive offset to the network input and output metrics in the access table.

Offset-list {in | out} offset [access-list] no offset-list {in | out} offset [access-list]

If the value of the parameter LIST is 0, then the OFFSET parameter is added to all measures. If the value of OFFSET is 0, then it has no effect. For IGRP, the value of the offset is added only to the delay. This subcommand also applies to RIP and hello routing protocols.

This offset can be cleared using the NO OFFSET- LIST command with the appropriate parameters.

In the following example, a router using IGRP adds an offset of 10: offset-list out 10 to the delay of all output metrics

Here is an example of adding the same offset to the access table 121:

Offset-list out 10 121

17. What five pieces of information does each router need to know when looking for a route?

All routers need the following information to route the message:

◎ destination address: the destination host to which the message is sent.

Determination of ◎ neighbor stations: indicates who is directly connected to the interface of the router.

Discovery of ◎ routes: discover which networks are known by neighboring stations.

◎ routing: provides the optimal (metric-dependent) path to the destination through information learned from neighboring stations.

◎ keeps routing information: the router keeps a routing table that stores all the routing information it knows.

18. Are the routing protocols supported by Cisco routers compatible with those of devices from other manufacturers?

All routing protocols supported by IGRP and EIGRP,Cisco routers are compatible with the same protocols implemented by other manufacturers. IGRP and EIGRP are patented products of Cisco.

19. What does the information about the entries in the RIP routing table indicate?

Each entry in the RIP routing table provides certain information, including the final destination address, the next-hop address to the destination, and the metric. This metric represents the distance (number of hops) to the destination terminal. Other information can also include.

Router issues add:

1. Do Cisco3600 series routers currently support WAN interface cards WIC-2T and WIC-2A/S?

Cisco3600 series routers support WIC-2T and WIC-2A/S WAN interface cards in 12.007XK and above.

But it is important to note that:

Only the Fast Ethernet hybrid network module can support these two WAN interface cards.

The network modules that support these two interface cards are as follows:

NM-1FE2W, NM-2FE2W, NM-1FE1R2W, NM-2W .

The Ethernet hybrid network module does not support it, as follows:

NM-1E2W,NM-2E2W, NM1E1R2W .

2. What is the maximum different / synchronization rate supported by the 8A/S network module and the WIC (2A/S WAN interface card) of Cisco3600 series routers?

These network modules and WAN interface cards can support both asynchrony and synchronization. The maximum asynchronous rate supported is 115.2Kbps, and the maximum synchronous rate is 128Kbps.

3. What are the cables for WIC-2T and WIC-1T?

WIC-1T:DB60 to V35 or RS232, 449 and other cables. Such as: CAB-V35-MT.

WIC-2T: smart to V35 or RS232, 449 and other cables. Such as: CAB-SS-V35-MT.

4. What is the difference between MCE1 on the Cisco 7000 series and E1 and CE1 on the Cisco 2600 Universe 3600?

MCE1 on Cisco 7000 can be configured as E1, CE1, while E1 and CE1 on Cisco 2600Universe 3600 only support their own functions.

5. Do Cisco 2600 series routers support inter-VLAN routing? what is the need for IOS software?

Cisco (in 2600 series routers, only Cisco2620 and Cisco2621 can support inter-VLAN routing (inter-VLAN routing is supported on 100-megabit ports). And if inter-VLAN routing is supported, the IOS software must include the IP Plus feature set.

6. What is the difference in hardware between the Cisco3660 router and the 3620amp 3640 router?

The differences are as follows:

* the basic configuration of the Cisco3660 router includes 1 or 2 10max 100m adaptive Fast Ethernet interfaces, while the Cisco3620/3640 basic configuration does not include Ethernet interfaces.

* Cisco3660 routers support hot-swappable network modules, while Cisco3620/3640 does not support hot-swappable network modules.

* the redundant power supply for Cisco3660 is built-in, while the redundant power supply for Cisco3620/3640 is external.

7. Why can't 3640 recognize NM-1FE2W?

Need to upgrade IOS to 12.0.7T

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