VLAN—Virtual LAN
As the network is gaining in popularity, the demand on the network in some enterprises is increasing sharply, and the scare of their internal corporate networks become larger and larger. Along with this situation the attendant security, network performance problems are the troubles for network administrators. However, VLAN technology, has solved the series of problems.
Firstly，At the first, people used HUB to linkmany clients to the network, and the HUB provided a public cable for the clients, as more and more users were accessed to the network, the broad band for each user was scale-down. For example : To link 10 HUB users with 10M Ethernet, then each user has to share bandwidth 10M/10—1M. Obviously, the way with sharing hub has been unable to meet the increasing demand for surge of network scale.People began to use switches to replace the hub. Switches access each user to provide a dedicated data channel, which is no longer similar to the HUB as a whole to share bandwidth.Although the bandwidth solved the distribution problem, but as more and more users access the network, people have found a new problem: Any arbitrary news will be broadcasting for all users in the network, the greater the size of network, the greater broadcasting on the scope, the performance of the entire network has become so intolerable to the customers because of broadcasting.At this time, network administrators use the router (which can be isolated broadcasting domain) to divide the bloated network into a number of smaller networks, the problem seems to have been resolved, but because the router only has few interface links to up the expense, so make the sub-tasks to the high cost on this network.
The switch has a number of interfaces, and transmit the data faster, but could not prevent the spread of the broadcasting;
Routers can prevent the broadcasting domain, but only a few interfaces for large networks subparagraph, the costs are too high, and because the speed delay to extend the time, it may reduce the network performance in a certain.
If there was certain technology or equipment to resolve this conflict on the issue then we can improve network performance greatly.
Secondly，At the first, a company with the Ministry of Finance, technical and sales departmets links the three office floors through computer switches together into the company network.We can envision a situation in such an interconnection, there is no security of the network environment, the three departments of office PCs can visit each other arbitrarily,The results will be that the monthly financial statements are passed round for perusal in all the company, sales of customer lists flow into the hands of those evil-intentions employees, the core technology information about the company’s products are showed to all staff… this is a very terrible thing! Then how to solve this kind of problem?
1. These three departments use an independent computer network, and not to link to the company network?
2. To separate the three departments networks with Routers, then control the visit with the visit list?

VLAN technology can solve the security and network performance problems.
VLAN technology allows two-story equipment with a three-tier broadcasting equipment isolation functions, and cam also blcok different VLAN members to exchange of visits.

Take catalyst switches to Cisco as an example. When the switch defined a VLAN and then adds its interface, then those specified interface will become a member of the VLAN, as the following graphs:
In a CISCO 1900 catalyst switches, it was divided two VLANs (left is the accounting VLAN, the right is management VLAN)

The switches’ port 1 to port12 are distributed to the accounting VLAN, port13 to port 24 are assigned to the Management VLAN. Since the switch does not allow broadcasting between the VLANs, so it means that the switches divided the network in the graph into sectors logically.

workstation A send a broadcasting to the network, then all workstations in the accounting VLAN will receive this broadcasting, but the switch will not send this broadcasting to any port on the management VLAN.In fact, the second-level switch will not send a frame to another VLAN. If indeed there is such a need, they can consider using routers or multilayer switches to communicate with each other between different VLAN.
For different VLAN, we can recards them as two independent network segments to each other on both logical and physical, on these two network segments, if need be through transmition then the best solution is to address through a third layer to enable them to exchange.
Pay attention to following problems when divide the VLAN::
1.Different vendors VLAN breakdown of the equipment may not be compatible;
2.After defined the VLAN, remember to add the members to their corresponding interfaces into the VLAN, otherwise VLAN will be invalid.
Problems must be attentionsed when one VLAN is used to numbers of swiches:
1.Trunk must be opened
2.VLAN must be corresponded
3.The interface of trunk must be achieving 100M Full Duplex
problems in doing different VLANs with one-arm Router to communicate:
1.Router’s trunk must be 100M Full Duplex
2.Do not configure IP to Router’s trunk, and do remain “no shutdown”.
3.The sub-interfaces which corresponds to the Routers, must match the VLAN.
Refer to following two samples:
Refer to the exhibit. How many broadcast domains exist in the exhibited topology?

A: one
B: two
C: three
D: four
Correct Answers: C
The topic test the CISCO candidates’ ability on division of the broadcasting and VLAN domain and understanding on basic functions. How many broadcasting domains are there in following graph? Careless candidates will choose A in a hurry, because the switch is not broadcasting in isolation, all the switches connected clients are in jurisdictions with the same broadcasting domain.In this question, network administrators divided the same VLAN on both of the switches — 3 VLANs across two switches. Each VLAN is a broadcasting domain, aso the answer is C.

Refer to the exhibit. The network administrator has created a new VLAN on Switch1 and added host C and host D. The administrator has properly configured switch interfaces FastEthernet0/13 through FastEthernet0/24 to be members of the new VLAN. However, after the network administrator completed the configuration, host A could communicate with host B, but host A could not communicate with host C or host D. Which commands are required to resolve this problem?

A: Router(config)# interface fastethernet 0/1.3
Router(config-if)# encapsulation dot1q 3
Router(config-if)# ip address 192.168.3.1 255.255.255.0
B: Router(config)# router rip
Router(config-router)# network 192.168.1.0
Router(config-router)# network 192.168.2.0
Router(config-router)# network 192.168.3.0
C: Switch1# vlan database
Switch1(vlan)# vtp v2-mode
Switch1(vlan)# vtp domain cisco
Switch1(vlan)# vtp server
D: Switch1(config)# interface fastethernet 0/1
Switch1(config-if)# switchport mode trunk
Switch1(config-if)# switchport trunk encapsulation isl
Correct Answers: A
As the graph, network administrators add a new VLAN3 on the S1, and add the F0/14 and F0/13 of S1 as VLAN3 members. But when all configuration is completed, administrators found VLAN2 members can exchange visits, but VLAN2 and VLAN3 members can not visit each other. To solve this problem, which orders must be added to the router? Analysis : within the same VLAN members exchange visits are no additional configuration, but different VLAN visits need the support of router.
From the graph, Router1 shows that the router connects two networks: 192.168.1.0 and the network of 192.168.2.0, but the lack of subnet 192.168.3.0 routing. The problem is right here. As long as the routers add a new sub-interface, the configuration of the network 192.168.3.0 of this can be resolved by mutual visits between different VLANs. So the answer is A.

Pass4sure practice exam No.7
7.The command frame-relay map ip 10.121.16.8 102 broadcast was entered on the router. Which of the following statements is true concerning this command?
A: This command should be executed from the global configuration mode.
B: The IP address 10.121.16.8 is the local router port used to forward data.
C: 102 is the remote DLCI that will receive the information.
D: This command is required for all Frame Relay configurations.
E: The broadcast option allows packets, such as RIP updates, to be forwarded across the PVC.
Correct Answers: E

The question tests the CISCO candidates’ understanding on the static mapping of Frame-relay. The command frame-relay map ip 10.121.16.8 102 broadcast was entered on the router. Which of the following statements is true concerning this command?
The candidates who are familiar with Frame-relay all know that the command is configured to the router under the interface mode, but option A said the order command is configured in the global mode, it is obviously wrong;
For the command of frame-relay map ip 10.121.16.8 102 broadcast, it means to mapping the distal IP to the local DLCI. Option B said this IP is the local routers’ IP, while option C said 102 of DLCI is remote one, it is obvious that B and C are wrong options;
For option D, not all of the Frame-relay needs configuration, for example, when the Frame-relay supports Reverse ARP analyze, the command would not need configuration, the D is also wrong.
Pass4sure practice exam No.24
24.Refer to the exhibit. Which statement describes DLCI 17?

A: DLCI 17 describes the ISDN circuit between R2 and R3.
B: DLCI 17 describes a PVC on R2. It cannot be used on R3 or R1.
C: DLCI 17 is the Layer 2 address used by R2 to describe a PVC to R3.
D: DLCI 17 describes the dial-up circuit from R2 and R3 to the service provider.
Correct Answers: C
Refer to the exhibit, the interfaces of R2 are configured with FR, and designated DLCI with No. 17. The role of DLCI is that when there are data sent out from R2 to R3, which PVC should be handed over the data.
1, Question
Now to configure a related command of frame-relay to the router: frame-relay map ip 10.121.16.8 102 broadcast.
2, requirements
For the describing of the options, which is correct in the following statement about the parameters of the command?

Frame-relay technology belongs to WAN technology, but its core reference model is still the standard, then it is our OSI. (Here, I would like to reiterate once again the importance of the OSI model; the candidates must master it well) Why we should configure map ip in interface? This command corresponds to which layer functions of OSI?
The command of map ip is to configure the Mapping of “agreement - address” to the link of frame-relay. Speaking of the mapping of “agreement - address”, we will naturally remember the ARP in Ethernet. We take the work mechanism of ARP as the reference, and then start analysis on command’s parameters in map ip of frame-relay.
In common Ethernet environment, and when host A wants to communicate with a network-paragraph host B, host A will start to Packaging data with top-down order, if A knows host B’s IP address is 192.168.1.2 then when it packages the data packet in the network layer, it will complete the packet header successfully, but when the data packets to continue Packaging to the bottom, there will be a problem - what’s the physical address of host B? ? ? In the second layer, the addressing is achieved through the MAC address. At this point, there is no way of knowing the target MAC address, and Packaging becomes impossible. One solution is using ARP. When A wants to communicate with B, A will check its ARP cache Table at first to see if there is a mapping record about agreements address of B(the relationship of mapping from IP to MAC) and, if so, access to data package directly; If not, send a broadcast report of goal Address with the entire text of F at first, to search B’s MAC address from the network’s, after received the Unicast response of B, then A will record the information in the A ARP cache table.
In a same link, it is not enough to just know each other’s network layer address for the two sets of equipments; they also need to know the addressing information between the two layers. Frame-relay technology is the connection-oriented transport protocol which works in the second layer; it requires addressing information of Layer 2 and Layer 3 to communicate the two sites through PVC. Different from Ethernet, its second layer information is not the MAC of a specific host, but DLCI (Data Link Connection Identifier).

We can use two methods to enable the mapping agreement addresses maintain normal relations.
1, To configure it through hand static.
The command is showed as the sample
Frame-relay map: This mapping command can create a mapping reached remote agreement address in static.
As detailed in the next example:

2, Use of frame-relay reverse ARP (Inverse ARP)
Frame-relay reverse ARP will provide the method to connect the address of the distal third layer and the DLCI of the local second layer through a non-manual way.
Pass4sure practice exam No.64
64.Refer to the exhibit. What is the meaning of the term dyn
mic as displayed in the output of the show frame-relay map command shown?

A: The Serial0/0 interface is passing traffic.
B: The DLCI 100 was dynamically allocated by the router.
C: The Serial0/0 interface acquired the IP address of 172.16.3.1 from a DHCP server.
D: The DLCI 100 will be dynamically changed as required to adapt to changes in the Frame Relay cloud.
Answer B
The status of router frame-relay interfaces can be checked by the command of “show frame-relay map” . In above exhibit, dynamic means the mapping relations of dlci and ip is achieved through Inverse ARP access to the dynamic. So the correct answer is B.

1, DR—Designated Router
The task of DR

In the exhibit, when the Direct Connect of a network which linked R3 interrupted, then R3 will only send the information to R1 (DR), after received the message, DR will send the information about the network interruption to the R2 and R4. In other words, R1 (DR) is the leader of the entire OSPF network, it has to report to DR for any changes in the network, and then from DR to send the news to the other routers.
2, BDR—Backup Designated Router
The task of BDR: in above exhibit, as if DR, the managers of the entire OSPF network, meets accidents and down, then the whole network will be confused because lose the core. The role of BDR is to become a new DR when the previous DR is invalid.
3, Why choose DR, BDR?
Let’s check what the network will look like if there is no DR / BDR:
As the exhibit shows, when R2 routers has news about updated information of routers and needs to send the news to other routers then it will copy the information three times to R1、 R3、R4 respectively.

When R1, R3, R4 received an updated report from R2, will do the same thing - because they are uncertain whether the other routers know this has been updated, so they will do their best to transfer out all the news they got through OSPF interface.

It will lead to a problem: the update information in the network will be copied many times and will take up much valuable network resources. If there is only one leader as DR and a BDR, then the issue will be resolved: all non-DR and non-BDR routers who get update information will only tell it to DR and BDR, and then the updated information will be transmitted to other routers by DR.
4, How to choose DR and BDR?
Refer to following exhibit; the Router IDs of four OSPF routers have been marked. They exchange the information by using HELLO report, thereby choosing a DR, BDR. Throughout OSPF network, the highest Router ID will become the DR; the sub-highest one will become the BDR, the rest ones known as DRother. In the following exhibit, because the Router ID of R1 is the highest, so to be the DR; While the Router ID of R2 is sub-highest, and to be the BDR; and R3, R4 are called DRother.

5. Configure DR, BDR Manually
DR has to update information of the whole network in time and perform the responsibility of as the leader of the entire OSPF network, so it needs strong performance as the DR router. Do not rule out the possibility: a network of low-end router is elected as the DR because of its larger numerical IP, and then it will be the bottleneck of the whole network. We can control elections through manual methods to specify who will become the DR and who will become the BDR.
There are two methods:
To designate DR、BDR by controlling the Router ID of each Router.
The election DR, BDR of each OSPF router is by comparing their respective Router ID to decide whose Router ID highest, who will become the DR. Then we can manually designate the Router ID of each Router to control elections. For example, in above exhibit, we are amending DR and BDR are R4, R3, while R1, R2 will become DRother.
Router1(config)#int lo 0
Router1(config-if)#ip add 1.1.1.1 255.255.255.0
Router1(config-if)#router ospf 100
Router1(config-router)#router-id 1.1.1.1
Router2(config)#int lo 0
Router2(config-if)#ip add 2.2.2.2 255.255.255.0
Router2(config)#router ospf 200
Router2(config-router)#router-id 2.2.2.2
Router3(config)#int lo 0
Router3(config-if)#ip add 3.3.3.3 255.255.255.0
Router3(config)#router ospf 300
Router3(config-routre)#router-id 3.3.3.3
Router4(config)#int lo 0
Router4(config-if)#ip add 4.4.4.4 255.255.255.0
Router4(config)#router ospf 400
Router4(config-routre)#router-id 4.4.4.4
Because the network has been presented in above exhibit, DR, BDR have been elected, if we re-amend the Router ID of each router at this time, they will not elect again, it would cause the network unrest. Therefore, after we changed the configuration, need to restart OSPF process manually:
Clear ip ospf pro
Y

Then check whether the configuration will be into force or not by the command of “show ip OSPF neighbor”.

2. By modifying router priority to control the election of DR, BDR.
In the election, Routers need to compare Router ID and priority level, the default priority is the same, and both are 1. So by default, only need to compare Router ID. However, manual changes it can control the election by change the priority level manually.

Methods are as follows:
For example, in above exhibit, we need to change R3 as DR, R1 as the BDR and the rest are for DRother
R3(config-if)#ip ospf priority 100
R1(config-if)#ip ospf priority 80

Priority areas are 0 to 255, when the priority of a router is 0, the router will not participate in the election.
Pass4sure practice exam No.100
100.A network administrator is troubleshooting the OSPF configuration of routers R1 and R2. The routers cannot establish an adjacency relationship on their common Ethernet link. The graphic shows the output of the show ip ospf interface e0 command for routers R1 and R2. Based on the information in the graphic, what is the cause of this problem?

A: The OSPF area is not configured properly.
B: The priority on R1 should be set higher.
C: The cost on R1 should be set higher.
D: The hello and dead timers are not configured properly.
E: A backup designated router needs to be added to the network.
F: The OSPF process ID numbers must match.
Correct Answers: D
As can be seen from the exhibit, R1, R2 hello interval, the invalid time of hello, hello waiting time were all not matched, so they can not form the neighbor relations.
Pass4sure practice exam No.140
140.The OSPF Hello protocol performs which of the following tasks? (Choose two.)
A:It provides dynamic neighbor discovery.
B:It detects unreachable neighbors in 90 second intervals.
C:It maintains neighbor relationships.
D:It negotiates correctness parameters between neighboring interfaces.
E:It uses timers to elect the router with the fastest links as the designated router.
F:It broadcasts hello packets throughout the internetwork to discover all routers that are running OSPF.
Correct Answers: A, C
The two tasks of Hello protocol:
It provides dynamic neighbor discovery.
It maintains neighbor relationships(keep alive).

Pass4sure practice exam No.101
101.On which types of network will OSPF elect a backup designated router?
A: point-to-point and multiaccess
B: point-to-multipoint and multiaccess
C: point-to-point and point-to-multipoint
D: nonbroadcast and broadcast multipoint
E: nonbroadcast and broadcast multiaccess
Correct Answers: E
In peer-to-peer networks, do not need to choose DR \ BDR. NBMA network needs to elect the DR \ BDR

1、 AS—autonomous system
Autonomy System is a large-scale network, usually run External Gateway Protocol in the internal of AS, and Border Gateway Protocol between the ASs.
Usually run OSPF、RIP、IS-IS、EIGRP and etc. in the internal of AS.
Definition of AS–Within a certain range, a group set of routing equipments which use the same routing protocol.
2、 Interface
The interface we usually referred to does not mean real physical interface. It is a virtual interface.
3、 Neighbor
When the two routers are interconnected with a shared link, and share the routing information, then they can say to each other neighbors.
Refer to following sample:
P1R1#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 1 FULL/BDR 00:00:34 192.168.12.2 Serial1/1
3.3.3.3 1 FULL/BDR 00:00:36 192.168.13.3 FastEthernet0/0
4、 Area
Area is the properties of the router’s interface but not the router itself. In the below graph, the three routers, A、B、C are in the internal of Area1, but the three interfaces of D router are in Area0, and the rest one is in Area1.

5. Internal routers
Internal routers refer to the routers whose interfaces are all in a same regional, they have the same topology table. For example presented above A, B, C and E are all “internal routers.”
6、 Router ID
It’s the ID for the router when it runs OSPF, each router will have an OSPF Router ID.
Router ID is generated by comparing each interface’ IP of the router itself.

There are three rules:
6.1. Priority of the highest. The highest IP will become the Router ID.
6.2. The loopback interface has the highest priority, while the router configurates the physical interface and loopback interface at the same time, the address of loopback interface will become the Router ID. If there are multiple loopback addressed, then take the first principle: Priority of the highest.
6.3. To designate a Router IDO by manually input an order

7. The functions of Router ID
The three routers, A、B、C are connected to each other, A send a message about routing updates to B, and from B to C, because C and A are also connected directly, then whether C should send this message to A? How C is aware of that this message is first sent by A? Router ID here played a crucial role; routers get the updated information in the Router ID of routing A, then know that it needs not to send the message back to A.
Refer to following sample:
P1R1#sh ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 992 0×80000002 0×00CE19 2
2.2.2.2 2.2.2.2 988 0×80000005 0×00D9FE 2

8, OSPF Measurement
Unlike distant vector routing protocol, OSPF takes bandwidth as the sole criterion. The default measurement is 108 metric / bandwidth.
Please refer to following sample:
P1R1#sh ip ospf int
Serial1/1 is up, line protocol is up
Internet Address 192.168.12.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 64
Loopback0 is up, line protocol is up
Internet Address 1.1.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type LOOPBACK, Cost: 1
Loopback interface is treated as a stub Host
FastEthernet0/0 is up, line protocol is up
Internet Address 192.168.13.1/24, Area 1
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1
1. Algorithm of Measurement for the link of serial1/1
P1R1# sh int s1/1
Serial1/1 is up, line protocol is up
Internet address is 192.168.12.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
108/1544=64
2. Algorithm of Measurement for the link of F0/0
P1R1#sh int fa0/0
FastEthernet0/0 is up, line protocol is up
Internet address is 192.168.13.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
108/100000000=1

Pass4sure practice exam No.46
46.On point-to-point networks, OSPF hello packets are addressed to which address?
A: 127.0.0.1
B: 172.16.0.1
C: 192.168.0.5
D: 223.0.0.1
E: 224.0.0.5
F: 254.255.255.255
Correct Answers: E
In point-to-point network, OSPF does not choose DR / BDR, all the HELLO packets send to 224.0.0.5

Pass4sure practice exam No.61
61.Refer to the exhibit. Router1 was just successfully rebooted. Identify the current OSPF router ID for Router1.

A: 190.172.32.10
B: 208.149.23.162
C: 208.149.23.194
D: 220.173.149.10
Correct Answers: C

When Router1 is just restarted, which interface’s IP will the ROUTER ID of OSPF?
As above mentioned, OSPF has certain rules for the choice of Router ID:
1. Priority of the highest. The highest IP will become the Router ID.
2. The loopback interface has the highest priority, while the router configurates the physical interface and loopback interface at the same time, the address of loopback interface will become the Router ID. If there are multiple loopback addressed, then take the first principle: Priority of the highest.
3. To designate a Router IDO by manually input an order

This question can use the second rule directly:
The principles that can be directly used two: the physical interface and loopback interface coexist, so choose 208.149.23.194

Pass4sure practice exam No.3456.Which three statements are correct about RIP version 2? (Choose three.)A:It has the same maximum hop count as version 1.B:It uses broadcasts for its routing updates.C:It is a classless routing protocol.D:It has a lower default administrative distance than RIP version 1.E:It supports authentication.F:It does not send the subnet mask in updates.

Correct Answers:  A, C, E

Basic knowledge of RIP:RIP protocol is an open routing protocol, it belongs to distance vector routing protocol, it has the common attributes of routing vector routing protocol. RIP updates the routing information periodically by outside broadcast (multicast) the routing table.Several Characteristics of RIP：1.Update timeV1 and V2 versions update at the same time, both are updated through 30S sending out the routing.2.Methods for update RIP V1 sends its whole routing table to its neighbor router by broadcasting. (255.255.255.255) RIP V1 sends its whole routing table to its neighbor router by multicast.（224.0.0.9）3.Administrative distanceRIP V1 and V2 have the same administrative distance: 1204.Measurement valueRIP V1 and V2 have the common attributes of distance vector routing protocol, measurement value is achieved by hop count.5.SecurityRIP V1 doesnt support authentication, RIP V2 supports authentication.6.The grant network supportBecause of the significant deficiencies of RIP, RIP V1 and V2 are not well to solve the problem, they have the biggest restrictions of hops, 15 hops. So they both can’t be used in the grant network environment.To solve RIP routing loop, here are some methods:1、Routing Failure 2、promote the update 3、Inhibition of time 4、The level of segmentation 5、Poison Routing6、Reversal poisoned 7、The largest hops 

Pass4sure practice exam No.104104.Refer to the exhibit. The network shown in the exhibit is running the RIPv2 routing protocol. The network has converged, and the routers in this network are functioning properly. The FastEthernet0/0 interface on R1 goes down. In which two ways will the routers in this network respond to this change? (Choose two.)
A:All routers will reference their topology database to determine if any backup routes to the 192.168.1.0 network are known.B:Routers R2 and R3 mark the route as inaccessible and will not accept any further routing updates from R1 until their hold-down timers expire.C:Because of the split-horizon rule, router R2 will be prevented from sending erroneous information to R1 about connectivity to the 192.168.1.0 network.D:When router R2 learns from R1 that the link to the 192.168.1.0 network has been lost, R2 will respond by sending a route back to R1 with an infinite metric to the 192.168.1.0 network.E:R1 will send LSAs to R2 and R3 informing them of this change, and then all routers will send periodic updates at an increased rate until the network again converges.Correct Answers:  C, D
Pass4sure practice exam No.117117.Which of the following are true regarding the command output shown in the display? (Choose two.)A:There are at least two routers participating in the RIP process.B:A ping to 192.168.168.2 will be successful.C:A ping to 10.0.15.2 will be successful.D:RtrA has three interfaces participating in the RIP process.Correct Answers:  A, C