Network engineers must know the network essence knowledge!

Router problems ：

1、 When to use multi routing protocol ？

When two different routing protocols want to exchange routing information , We need to use multi routing protocol . Of course , Routing redistribution can also exchange routing information . It is not necessary to use multi routing protocol in the following cases ：

• From the old version of the internal Gateway Protocol （ Interior Gateway Protocol,I G P） Upgrade to a new version of I G P.
• You want to use another routing protocol, but you must keep the original protocol .
• You want to terminate the internal route , To avoid interference from other routers that do not have strict filtering and supervision functions .
• You are in an environment composed of routers from multiple manufacturers .

What is distance vector routing protocol ？

The distance vector routing protocol is for Small network environment The design of the . In a large network environment , This kind of protocol is learning routing and security Holding the route will generate large traffic , Take up too much bandwidth . If in 9 0 The route sent by the adjacent site is not received within seconds Select table update , It thinks that adjacent sites are unreachable . every other 30 second , Distance vector routing protocol should send to neighboring sites The entire routing table , Update the routing table of adjacent sites . such , It can be from other sites （ Direct connection Or connected in other ways ） Collect a list of networks , For routing . Distance vector routing protocol uses hop Number as a measure , To calculate the number of routers to reach the destination .

for example ,R I P Use B e l 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 minimum number of hops . The maximum number of hops allowed is usually 1 5. Those must go through 1 5 More than router terminals 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 link state routing protocol ？

Link state routing protocol is more suitable for Big networks , But because of its complexity , Make the router need more C P U resources . It can find broken links or newly connected routers in a shorter time , Make the convergence time ratio of the protocol Shorter distance from vector routing protocol . Usually , stay 10 No message from the next station was received within seconds H E L LO message , It thinks that the next station No longer reachable . A link state router sends an update message to its neighbor , Notify all links it knows . It does The metric of determining the optimal path is a numerical cost , The value of this cost is generally determined by the bandwidth of the link . With minimum cost The link is considered to be optimal . In the shortest path first algorithm , The value of the maximum possible cost can be almost infinite .

If the network hasn't changed , The router only needs to refresh the routing table that has not been updated periodically （ The length of the cycle can be from 3 0 Minutes to 2 Hours ）.

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

A router can use both distance vector routing protocols , Use link state routing protocol again ？

Sure . Each interface can be configured to use different routing protocols ; But they must be able to exchange routing information through reassignment routing .

2、 What is an access table ？

The access table is a series of control data packets added by the manager and input in the router 、 Output rules . It is not generated by the router itself . The access table can allow or prohibit packets from entering or outputting to the destination . The entries of the access table are executed sequentially , That is, when the packet arrives , First, see if it is constrained by the first table item , If it is not , Then execute down in sequence ; If it matches the first entry , Whether allowed or prohibited , There is no need to check the following table items .

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

What types of access tables are supported ？

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

• IP Standard access table No ：1～9 9
• IP Extended access table number ：1 0 0～1 9 9
• IPX Standard access table No ：8 0 0～8 9 9
• IPX Extended access table number ：1 0 0 0～1 0 9 9
• AppleTa l k Access table number ：6 0 0～6 9 9

Hint at Cisco IOS Release11.2 Or above , You can use the named access table to determine the number in 1～199 Access table for .

How to create IP Standard access table ？

One I P The creation of standard access table can be completed by the following command ： Access-list access list number {permit | deny} source [source-mask]

In this order ：

• access list number： Determine which access table this entry belongs to . It's from 1 To 9 9 The number of .
• permit | deny： Indicates whether the entry allows or blocks the flow of information from a specific address .
• source： Determine source I P Address .
• source-mask： Determine which bits in the address are used for matching . If a bit is "1", It indicates that the bit in the address is independent , If it is "0" Words , Indicates that this bit in the address will be used for matching .

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 to use route redistribution ？

Route redistribution is usually in those responsible for learning routes from an autonomous system , A router that then broadcasts to another autonomous system Configure on . If you are using IGRP or EIGRP, Route redistribution is usually performed automatically .

4、 What is management distance ？

Management distance refers to the routing reliability of a routing protocol . Each routing protocol ranges from high reliability to low reliability , Assign a trust level in turn , This level of trust is called management distance . For two different routing protocols to a destination routing message Rest , The router first determines which protocol to trust according to the management distance .

6、 How to configure reallocation ？

Before route reallocation , You have to first ：

1) Decide where to add a new agreement .

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

3) Decide which protocol is at the core , Which is on the border .

4) Determine the direction of route reallocation .

You can use the following command to reallocate route updates （ This example is for OSPF Of ）：

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

In this order ：

• protocol： Indicates the source routing protocol that the router wants to reallocate routes . The main values are ： bgp、eqp、igrp、isis、ospf、static ip 、connected and rip.
• process-id： To specify OSPF The process of ID.
• metric： Is an optional parameter , The metric used to indicate the reassigned 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 a router fails , Other routers can converge in an acceptable time . But in large networks , A router may find a fault with a large delay . Know that adjacent routers can accelerate convergence , Because the router can know the faulty router faster , because hello The interval between messages is shorter than the interval between routers exchanging information .

A router using distance vector routing protocol does not send routing update information when the adjacent router does not send routing update information , To find that the adjacent router is unreachable , This time is generally 10～90 second . The router using link state routing protocol does not receive hello The message can be found that the adjacent router is unreachable , This interval is generally 10 Second .

How distance vector routing protocol and link state routing protocol find adjacent routers ？

A router using distance vector routing protocol needs to create a routing table （ This includes the network directly connected to it ）, At the same time, it will send the routing table to the router directly connected to it . The adjacent router merges the received routing table into its own routing table , At the same time, it should also send its own routing table to its adjacent router . Routers that use link state routing protocols create a link state table , Include a list of destinations for the entire network . In the update message , Each router sends its entire list . When the adjacent router receives this update message , It copies the content , At the same time, send the information to its adjacent station . There is no need to recalculate when forwarding the contents of the routing table .

Pay attention to IGRP and EIGRP Router broadcast hello Message to find adjacent stations , At the same time like OSPF Same as exchanging routing update information .EIGRP Save a neighbor list for each network layer protocol , It includes the address of adjacent stations 、 The number of messages waiting to be sent in the queue 、 The average time required to receive or send messages from or to neighboring stations , And the time when no message is received from the adjacent station before determining that the link is disconnected .

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 On , Also connected to Internet On ; It can be a multi LAN interconnected by the enterprise backbone network . All routers must be connected to each other in an autonomous system , Run the same routing protocol , Assign the same autonomous system number at the same time . Links between autonomous systems use external routing protocols , for example B G P.

9、 What is? BGP？

BGP(Border GatewayProtocol) It 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 , It USES IGP And common metrics to forward messages to other autonomous systems .

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

10、BGP Supported conversation types ？

BGP The session between adjacent routers is established on TCP Above the agreement .TCP The protocol provides a reliable transmission mechanism , Two types of sessions are supported ：

• external BGP（EBGP）： Is a session between routers belonging to two different autonomous systems . These routers are adjacent , Share the same media and subnet .
• Inside BGP（IBGP）： Is a session between routers within an autonomous system . It is used to coordinate and synchronize routing processes within autonomous systems .BGP The router can be anywhere in the autonomous system , Routers can be separated by... Or even in the middle .

Be careful :" The content of the initial data flow is the whole BGP Routing table . But when the routing table changes in the future , The router transmits only the changed part .BGP There is no need to update the entire routing table periodically . therefore , While the connection has been established , One BGP The sender must save the entire network shared by all routers at the same level BGP Routing table .BGP The router periodically sends Keep Aliv Message to confirm that the connection is active . When an error or special situation occurs , The router sends Notification news . When a connection fails , Will produce a notification Message and disconnect ."- come from RFC11654、BGP* do .

11、BGP Allow route redistribution ？

allow . because BGP It is mainly used for routing between autonomous systems , So it must support RIP、OSPF and IGRP Synthesis of routing table , In order to transfer their routing table to an autonomous system .BGP Is an external routing protocol , So it's * Different from an internal routing protocol . stay BGP in , Only when a route already exists IP When in the routing table , Ability to use NETWORK Command in BGP Create a route in the route table .

12、 How to display all... In the database BGP route ？

To display all... In the database BGP route , Just in EXEC Type... On the command line ：

show ip bgp paths

The output of this command may be ：

Address Hash Refcount MetricPath
0 x 2 9 7 A 9 C 0 2 0 i

13、 What is horizontal segmentation ？

Horizontal segmentation is a technology to avoid the emergence of routing rings and speed up routing convergence . Because the router may receive its own routing information , And this information is useless , The horizontal segmentation technology does not reverse announce any route update information received from the terminal , And only those routes that will not be cleared due to counting to infinity .

14、 How the routing ring is generated ？

Due to the existence of network route convergence time , The new route or changed route in the routing table cannot be stable in the whole network very quickly , Make inconsistent routes exist , Then a routing ring will be generated .

15、 What is a measure ？

The measure represents the distance . They are used to determine the optimal route when looking for a route . Each routing algorithm generates a routing table , A value is generated for each path through the network （ measurements ）, The smallest value represents the optimal path . The measurement can be calculated considering only one feature of the path , But more complex metrics are generated by combining multiple characteristics of the path . Some common measures are ：

◎ Skip steps ： The number of router output ports through which the message will pass .

• Ticks： Delay of data link （ about 1/18 Per second ）.
• cost ： Can be an arbitrary value , Is based on bandwidth , Fees or other calculation methods defined by the network manager .
• bandwidth ： The capacity of the data link .
• Time delay ： The length of time the message is transmitted from the source to the destination .
• load ： The size of the part of the network resource or link that has been used .
• reliability ： The ratio of error bits of the network link .
• Maximum transmission unit （MTU）： The maximum message length that all links can accept on a path （ The unit is byte ）.

IGRP What type of routing metrics are used ？ What does this measure consist of ？

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

• bandwidth ： Minimum bandwidth value between source and destination .
• Time delay ： Interface delay accumulated in the path .
• reliability ： The worst possible reliability from source to destination , Based on the state of the link hold .
• load ： The worst-case load of the link between the source and the destination , Expressed in bits per second .
• MTU： The smallest in the path MTU value .

16、 Can the measure be modified or adjusted ？

Add a positive offset . The complete structure of this command is as follows ： have access to OFFSET-LIST ROUTER The subcommand adds a positive offset to the network input and output measures in the access table .

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

If parameters LIST The value of is 0, that OFFSET Parameters will be added to all measures . If OFFSET The value of is 0, Then it has no effect . about IGRP Come on , The value of the offset is only added to the delay . This subcommand also applies to RIP and hello Routing protocol .

Use... With appropriate parameters NO OFFSET- LIST The command clears this offset .

In the following example , A use IGRP The router adds an offset to the delay of all output metrics 10：

offset-list out 10

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

offset-list out 10 121

17、 Each router needs to know which five parts of information when looking for a route ？

All routers need the following information to find a route for the packet ：

• Destination address ： Destination host of message sending .
• Determination of adjacent stations ： Indicate who is directly connected to the router interface .
• Route discovery ： Discover which networks the neighboring stations know .
• Choose a route ： Through the information learned from neighboring stations , Provide the best （ Related to measures ） The path to the destination .
• Keep routing information ： The router saves a routing table , It stores all known routing information .

18、Cisco Are the routing protocols supported by the router compatible with those of other manufacturers ？

except IGRP and EIGRP,Cisco All the routing protocols supported by the router are compatible with the same protocols implemented by other manufacturers .

IGRP and EIGRP yes Cisco Our patented products .

19、RIP What does the information of the entries of the routing table indicate ？

RIP Each entry of the routing table provides certain information , Include the final destination address 、 Next hop address and metric to destination . This metric represents the distance to the destination terminal （ Skip steps ）. Other information can also include .

Router problem supplement ：

1、Cisco3600 Whether the series routers currently support WAN interface cards WIC-2T and WIC-2A/S？

Cisco3600 Series routers are in 12.007XK And above support WIC-2T and WIC-2A/S These two WAN interface cards .

However, it should be noted that only the fast Ethernet hybrid network module can support these two WAN interface cards .

The network modules supporting these two interface cards are as follows ：

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

The Ethernet hybrid network module does not support , As shown below ：

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

2、Cisco3600 A series of routers NM(4A/S,NM(8A/S Network modules and WIC(2A/S The maximum difference supported by the WAN interface card / What are the synchronization rates ？

These network modules and WAN interface cards can support asynchronous , It can also support synchronization . The maximum asynchronous rates supported are 115.2Kbps, The maximum synchronization rate is 128Kbps.

3、WIC-2T And WIC-1T What kind of cables do you have ？

• WIC-1T：DB60 turn V35 or RS232、 449 Etc . Such as ：CAB-V35-MT.
• WIC-2T：SMART Type conversion V35 or RS232、 449 Etc . Such as ： CAB-SS-V35-MT.

4、Cisco 7000 On the series MCE1 And Cisco 2600/3600 Upper E1、 CE1 What's the difference? ？

Cisco 7000 Upper MCE1 It can be configured as E1、 CE1, and Cisco 2600/3600 Upper E1、 CE1 Only own functions are supported .

5、Cisco 2600 Series router , Do you support VLAN Routing between , Yes IOS What are the software requirements ？

Cisco(2600 In series routers , Only Cisco2620 and Cisco2621 Can support VLAN Between the route ( Only 100m ports can support VLAN Routing between ). And if it supports VLAN Routing between , requirement IOS The software must include IP Plus Feature set .

6、Cisco3660 Router and 3620/3640 What are the differences between routers and hardware ？

The differences are as follows ：

• Cisco3660 The basic configuration of the router includes 1 or 2 individual 10/100M Adaptive fast Ethernet interface ; and Cisco3620/3640 The Ethernet interface is not included in the basic configuration .
• Cisco3660 The router supports hot plug of network modules , and Cisco3620/3640 Network module hot plug is not supported .
• Cisco3660 The redundant power supply of is built-in , and Cisco3620/3640 The redundant power supply of is external .

7、 Why? 3640 Can't identify NM-1FE2W？

Need to put IOS Upgrade to 12.0.7T

Switch problems

About the switch ：

1、Catalyst 35500XL/2950XL How the stack of is implemented ？

• Special stacking cables are required ,1 Meters long or 50 Cm long (CAB-GS-1M or CAB-GS-50CM) And a dedicated Gigabit stack card GigaStack GBIC (WS-X3550-XL) ( This card already contains CAB-GS-50CM Stack cables ).
• May choose 2 Two stacking methods ： Chrysanthemum chain method ( Provide 1G The bandwidth of the ) Or point-to-point method ( Provide 2G The bandwidth of the ).
• 2 Both methods can be used for backup .
• Daisy chain method can support at most 9 Stack of switches , The point-to-point method can support at most 8 platform .

2、Catalyst 3550 XL When stacking series switches , Whether redundant backup is supported ？

Catalyst3550XL There are two ways to stack a series of switches ： Daisy chain mode and point-to-point mode . When using daisy chain , Stacked switches are connected in turn , Switch to switch 1Gbps The transmission bandwidth of ; When using a point-to-point approach , Need a separate Catalyst3508G-XL Switch , The rest of the switches are stacked GBIC Cards and stacked cables with 3508G Connected to a , This method can reach a maximum of 2Gbps Full duplex transmission bandwidth . 　

Both methods support stacked redundant connections . When using daisy chain connection , Redundant connection is accomplished by connecting the top switch to the bottom switch with stacked cables . When using point-to-point connections , Is through the use of 2 platform 3508 Switch to complete .

4、 Catalyst3550 XL A Gigabit port of the uses a stacking card to stack , Whether another Gigabit port can be connected to a Gigabit switch or a Gigabit server ？

Sure . Need to use 1000Base-SX GBIC or 1000Base-LX/LH GBIC.

5、 Ethernet Channel Tech. What network devices can be applied to ？ How to use ？

It can be applied between switches , Between switch and router , Between switch and server

Can be 2 Or 4 individual 10/100Mbps or 1000Mbps Port usage Ethernet Channel Tech., Up to 400M(10/100Mbps port )、4G(1000Mbps port ) or 800M(10/100Mbps port )、8G(1000Mbps port ) The bandwidth of the .

6、Ethernet Channel Technology What's the role ？

Increase bandwidth , Load balancing , Line backup

7、 When the port is set to Ethernet Channel when , How to select a line ？

According to the Ethernet source address and destination address of the data frame 1 Bit or 2 Bit do or operation , Decide which link to output from . For the router, it is based on the network address , To determine the output of the link .

8、Ethernet Channel Technology And PAgP (Port Aggregation Protocol ) The difference between ？

PAgP yes Ethernet Channel Enhanced Edition , It supports the Ethernet Channel Upper Spanning Tree

Protocol and Uplink Fast, And support automatic configuration Ethernet Channel The binding of .

• Minimum power required 1 2
• Packet forwarding rate 18Mpps 18Mpps
• backplane bandwidth 24Gbps 60Gbps

9、Catalyst4000 Whether the series supports ISL？

from Supervisor Engine Software Release 5.1 Start supporting .

10、Catalyst4000 Redundant power options for switches 4008/2 and 4008/3 What's the difference ？

Catalyst4003 There are two power slots on the switch chassis , When leaving the factory, it comes with a power supply ,4008/2 It is a customized redundant power supply .Catalyst4006 There are three power slots on the chassis of , The factory comes with 2 A power supply ,4008/3 It is a special redundant power supply customized for it .

11、Catalyst 4006 Whether the layer 3 switching module of does not contain Ethernet port ?

No ,Catalyst4006 The three-layer switching module of contains 32 individual 10/100 Adaptive ports and 2 Gigaports . stay 4003 It can replace the original when used on WS-X4232-GB-RJ modular , Thus, the network structure is not affected

12、Catalyst 4000 Series modular switches use Gigabit switching modules , How to select the two existing switching modules ( The product number is as follows )？

• WS-X4306-GB Catalyst 4000 Gigabit Ethernet Module, 6-Ports (GBIC)
• WS-X4418-GB Catalyst 4000 GE Module, Server Switching 18-Ports (GBIC)

The two modules are used in different environments

WS-X4306-GB It's a 6 Gigabit switching module of port , Each port has exclusive Gigabit bandwidth , It is suitable to be the backbone of the network , Used to connect switches with Gigabit interfaces ; It can also be connected to a server with a gigabit network card .

WS-X4418-GB It's a 18 Gigabit switching module of port , Two of the ports have exclusive Gigabit bandwidth , in addition 16 All ports share 8G Full duplex bandwidth , But each port can burst to Gigabit . This module is suitable for connecting Gigabit servers where servers are concentrated , It is not suitable for connecting to the network backbone .

13、Catalyst 6000 What is the backplane bandwidth and packet forwarding rate of the series ？

• Catalyst 6500 The backplane bandwidth of the series can be extended to 256Gbps, The packet forwarding rate can be extended to 150Mpps;
• Catalyst 6000 Series as a cost-effective solution to 32Gbps Backplane bandwidth and 15Mpps Packet forwarding rate .

14、Catalyst 6000 Series of MSFC How much is required M DRAM ？

Catalyst 6000 series IOS The software is stored in MSFC in , MSFC Ask for 128M DRAM. Default configuration includes 128M DRAM.

15、Catalyst 6000 Are there any restrictions on the slots on the series ?

Except that the first slot is dedicated to the engine , The second slot can be used to back up the engine or line card , Other slots are used for line cards .

16、Catalyst 6000 The series has several engines ？

Catalyst 6000 The engines of the series are divided into Supervisor Engine 1 and Supervisor Engine 1A Two kinds of , among

Supervisor Engine 1A There are two specific backup engines .

The models are as follows ：

model	describe
WS-X6K-SUP1-2GE Catalyst 6000 Supervisor Engine1 engine	Including two Gigabit ports ( Need to buy GBIC)
WS-X6K-SUP1A-2GE Catalyst 6000 Supervisor Engine1A engine	intensive QOS characteristic , Including two Gigabit ports ( Need to buy GBIC)
WS-X6K-SUP1A-PFC Catalyst 6000 Supervisor Engine1A engine	Including two Gigabit ports ( Need to buy GBIC) and PFC card
WS-X6K-S1A-PFC/2 Catalyst 6000 Supervisor Engine1A Redundant engine	Including two Gigabit ports ( Need to buy GBIC) and PFC card
WS-X6K-SUP1A-MSFC Catalyst 6000 Supervisor Engine1A engine	Including two Gigabit ports ( Need to buy GBIC) and MSFC、 PFC card
WS-X6K-S1A-MSFC/2 Catalyst 6000 Supervisor Engine1A Redundant engine ,	Including two Gigabit ports ( Need to buy GBIC) and MSFC、 PFC card

17、Catalyst 6000 Must the backup engine and the main engine be consistent on the series ？

Yes . Catalyst 6000 The backup engine of the series must be consistent with the main engine ,

for example , You can't leave it alone MSFC&PFC The engine to bring MSFC&PFC Engine for backup .

in addition , WS-X6K-SUP1A-PFC and WS-X6K-SUP1A-MSFC There is a dedicated backup engine .

Lord 、 The corresponding relationship of the standby engine is as follows ：

The main engine	Backup engine
WS-X6K-SUP1-2GE	WS-X6K-SUP1-2GE
WS-X6K-SUP1A-2GE	WS-X6K-SUP1A-2GE
WS-X6K-SUP1A-PFC	WS-X6K-S1A-PFC/2
WS-X6K-SUP1A-MSFC	WS-X6K-S1A-MSFC/2

18、Catalyst 6000 What are the routing protocols supported by the ？

Catalyst 6000 The series of supported routing protocols are ：OSPF, IGRP, EIGRP, BGP4, IS-IS, RIP and RIP II;

For multicast PIM Support sparse and dense Two modes ;

Supported non IP Routing protocols include ： NLSP, IPX RIP/SAP, IPX EIGRP, RTMP, Apple Talk EIGRP and DECnet Phase IV and V.

19、Catalyst 6000 What are the network protocols supported by the ？

MSM Upper support 6Mpps Of IP、 IP Multicast and IPX . On the engine MSFC Support 15Mpps Of IP、 IP Multicast 、IPX as well as AppleTalk、 VINEs、 DECnet.

20、Catalyst6000 If the engine is SUP-1A-2GE, How to realize the function of layer 3 switching ？

use MSM Realization . 6000 It only contains MSFC To get through MSFC Realize the three-layer switching function , stay 6000 On , MSFC Cannot be ordered separately .

21、Catalyst? 6000 Switch and Catalyst? 6500 What is the difference between switches ？6000 Whether the switch can be upgraded to 6500 Switch ？

Catalyst? 6000 The backplane bandwidth of the series switch is 32G, and 6500 The backplane bandwidth of the series switch can be extended to 256G. Because the backplane bus structures used by the two series of switches are different , therefore 6000 The switch cannot be upgraded to 6500 Series switches .

But these two series of switches use the same switching module .

22、Catalyst3508G Is it possible to work with Catalyst3524 Daisy chain stacking mode is also adopted ？

Absolutely. .

23、 Configure between switches Uplink-Fast when , Whether to close the original Spanning-Tree Options ？

Unwanted ,Uplink-Fast In fact, a simplified Spanning-Tree Algorithm , And standard Spanning-Tree compatible , Therefore, it is not necessary to turn off this function .