Feb

Changes in the switch port trigger cascading failures have no Internet access

Switch is a central hub for the LAN equipment, network size of the relatively large number of LAN switches are often used in quite a lot of changes in position between them may also be more frequent. In this working environment, network administrators must be based on the characteristics of switches, as well as the performance of the proper deployment, because our random deployment may be to the network's normal operation and maintenance to bring hidden dangers. Now, this article and share a cascade due to the switch port can trigger changes in the case of the Internet, hoping to bring to all of us to help efficiently manage local area network.

Failure

LAN in a building larger scale, there are about 300 computers distributed around the various floors, each floor units stationed in different, and some floors only a unit, and some floors that contain up to four units; the building in order to efficiently manage both networks, while ensuring the building units within the Gejia Internet security, network administrators can manage H3CS3050 selected model switch as a floor switch, and In the floor switch, in accordance with the number of units in different companies for the various units into a single virtual subnet of work, this way even if a network interior of their flats suffered a virus attack, it will not affect other units in the normal Internet access, at the same time network administrators to exclude a network failure, just to lock in a certain range of troubleshooting a virtual work of sub-networks without the need to conduct large-scale search, troubleshooting node.

After the network administrator of rational planning, correct configuration, the building work of the various units in the subnet can be a normal peacetime access to Internet network. Recently, however, there are a number of units moved into the building, in order to ensure that the personnel of these units can also be a normal Internet access, network administrators had to resort to the building some of the network upgrade. Now, network administrators will be located on the third floor of the S3 intends to switch placed on the fourth floor of floor, and let with the already placed on the fourth floor of the S4 floor switch cascade; previous floor switch S3 is through an exchange of port and building networks core switch cascading, in changing location of the switch into the use of two floors of the exchange of port and S4 cascading switches. Changes in the completion of the physical connection, the network administrator to discover, set in the floor of the switch S3 in the virtual work of five sub-networks, virtual work of six sub-networks can not normally access the Internet network, allowing network administrators can not understand why, That switch or switches, each virtual subnet configuration parameters work, there was no change, just change a bit cascade switch port on the switch into the virtual work of all the subnets why can not normally access the network out?

analysis of investigation

1, test switch status

After careful analysis, network administrators that support the Plug and Play functionality for those who switch, the change switch cascade port, the switch should not affect the corresponding sub-network under the virtual work of the working state, but now S3 cascade switch port floor location change, the division of the virtual switch in the work of five sub-networks, virtual work subnet 6 can not normally access Internet networks, and apparently the fault is due to the switch port changes in the cascade. Taking into account the floor switches S3 through S4 is now connected to the building floor switches in the network will not be a floor switch S4 is not a normal working state, causing the switch S3 floors of virtual work of the following sub-networks can not be normal access to Internet networks? With this in mind that network administrators to immediately switch from the S4 floors of virtual work of the following sub-network to find a computer to the Internet tests revealed that the computer can be a normal Internet; network administrator is still somewhat at ease, he chose the other successive online computer tests, test results are normal, indicating the working state of the switch S4 floor normal.

2, test cascade port status

After the above investigation, the network administrator to determine the problem lies in S3 floor switch, S4 floor cascade port on the switch, so he intended to check these two switching ports detailed configuration information. Note made up, the network administrator to immediately switch to control random with floor switch cable to connect to S3, and then HyperTerminal to log into the S3 switch back floor management system, the system's command-line status of implementation of the system command, switch into the system global configuration state, and then enter a string in the status of the command displayinterfaceethernet0 / 2, click the Enter key, the network administrator then the returned results from the interface found in S3 floor switch ethernet0 / 2 on the port is up state (shown in Figure 1), which shows that the cascading port is online enabled; follow the same methods of operation, the network administrator has logged into the S4 switch back floor management systems, and the global configuration of the system state, See the connection S3 cascade switch port floor working conditions and found that the cascade port switch S4 floor working conditions also in the up state. Check out the results of the network administrator once again fell into meditation, since the S3 floor switches, S4 floor cascade switch port working conditions are normal, then why can not switch S3 floor floor switch S4 to access Internet networks?

3, check the cascade port configuration

Following the removal of their own state as well as the cascade switch port status factors, the network administrator from S3 floors began to suspect that the cascade port configuration switches, and because of his previous S3 Floor the use of a switching-port switches and core switches cascade, but now using two floors of the exchange port and S4 cascaded switches will not be a cascade port changes in position, the following sub-net virtual work need to re-divide , configure it? Network administrator intends to compare the S3 first floor of an exchange of port on the switch ports to exchange between the two parameters to configure what is different, thought to do, he immediately in front of the operation method according to log into the admin interface, the switch S3 floors, and in global configuration mode followed by the implementation of the string command displayinterfaceethernet0 / 1, displayinterfaceethernet0 / 2, and then carefully compared the results of the two commands to return information; After careful comparison, network administrators found that an exchange of port Portlink-type values for the trunk, and 2 the exchange of port Portlink-type values for access (as shown in Figure 2), Is the exchange of port connection type changes resulted in the switch S3 floors of virtual work of the following sub-networks can not be normal access to Internet network?

Through the Internet search, network administrators can manage the switch was found for example, each switch port can be set to Access, Trunk, Multi links to three different types, which type of switch ports Access allows only one virtual work subnet, and it is typically used to connect an ordinary computer, Trunk type of switch ports to allow multiple virtual work subnet, and it is generally set at the cascade port, while the Multi type of switch ports to allow both a virtual work subnet too, but also work at the same time allows multiple virtual subnet, and it is the main purpose is both used to connect switches, and can be used to connect to the regular computer. We can at the same one switch at the same time set up to enable a different type of connection, but the type of exchange Trunk ports and Multi type of exchange can not be directly between the port switch, you must first transit through the Access to each type of switch. In accordance with the above analysis, the network administrator to easily locate the fault on the specific causes, that is, floor switches S3 and S4 to use two floors of the exchange-port switch cascading, the 2-Port Switch Portlink-type parameter is set incorrectly, resulting in corresponding to the switch following the work of multiple virtual subnets can not be exchanged through the two port network access.

Tip: Trunk is a kind of packaging technology, it is a point to point link, the main function is only through a link to connect multiple switches can be configured to extend the work of multiple virtual subnets; At the same time, Trunk links can be connected to a switch or a router or a server (special card), but also can be used by Trunk technology and superior way of cascading switches to expand the number of interfaces can be stacked to achieve similar functionality, saving the network hardware costs. In addition, Trunk link does not belong to any one sub-net virtual work, it's just in the network play the role of the pipeline. Trunk load of virtual work of sub-nets, the default is 1 under the 1005, can be modified, but must have a Trunk protocol. Using the Trunk, the two switches connected interface protocol to be consistent. Trunk link is configured to interface usually switch supports a maximum bandwidth of bandwidth mouth.

troubleshooting

figure out a specific cause of the malfunction, the number of virtual sub-network can not access the work of the fault phenomena also solved, and network administrators are now as long as the changes S3 floor switch configuration parameters, the 2-Port Switch Portlink-type parameter can be from Access into a Trunk, and so divided by a switch on the floor in the S3 sub-network 5 a virtual work, virtual work of six sub-networks can be adopted together with 2 switching port access Internet links. S3 modify the exchange floor switch 2 port link type parameters, the network administrator to control the first through the Console cable to connect directly to target the exchange, and then log on with administrator rights management system into the background, followed by the implementation of the string command system, switching switch the system into the corresponding global configuration state; following the implementation of the system global state of the string command interfaceethernet0 / 2, enter the 2-Port Switch view configuration mode, switch ports in the target view mode and then type the string to the command portlink-typetrunk, single - After hit return key, S3 floor switch 2-port link type was successfully modified in order to trunk; to make the switch S3 under the floor of the work of all the virtual subnets can be through the Trunk port access Internet network, network administrator at the two switch ports The view configuration mode, continue to implement the string command porttrunkpermitvlanall, As a division of S3 floor regardless of the number of switches on the virtual work of sub-networks, can be exchanged through the target port access. After the completion of the above configuration tasks, network administrators, and finally the implementation of the string command save, this time the system pops up the screen shown in Figure 3 the operation prompted, click the Y button on the keyboard, so that a switching system to S3 Floor these settings are automatically saved a good action.

In accordance with the operation of the same ideas, network administrator has logged into the S4 floor switches, and the background of the system will be connected to two switch ports using the port cascade link type is also modified in order to Trunk. Last, online testing, and indeed the switch S3 floors of all the virtual work of the following sub-networks can be a normal Internet access, and thus change the port from the cascading failures caused no Internet access were successfully removed.

Lessons Learned

In order to facilitate management and maintenance of networks while the network in order to avoid large-scale spread of the virus, and now almost all of the LAN is divided into a number of virtual subnets work, in this kinds of cases, to adjust or change the location of network devices is a common thing, and each time the network adjustment, the original division of the virtual work of subnets are often no longer effective, does it mean that network administrators need to re-take the effort to configuration parameters of the virtual work subnet do? In fact, the switches are often more intelligent, network administrators do not need to repeat the division, set up operation, just need to adjust the switch cascade port link type, we can make the virtual subnet on the work of the state from the Internet location of network equipment the impact of adjustment, and this way we can efficiently on the LAN network management and maintenance of the.