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But sw1 has, say, 10 and 20 vlan and sw2 has 40 and 50 vlans, then they will not communicate, if the ports are access too, and in this case we have to use trunking are created then it will not, we have to use trunking? The detail, as I mentioned above, is in the number of vlan that you configure in the interfaces of the link that connects the switches.
If you leave the interfaces that connect the switches in trunk mode, then the packets are not re-tagged, keeping the number of vlan so they were labeled by the first switch. Not being re-tagged, the packet is not retransmitted to the port with a different number of vlan, so the ping is no longer successful. This can be checked in your original topology if you leave the link that connects the switches in trunk mode.
After these changes the ping is no longer successful, because the packets are no longer re-tagged. Note that the ping is no longer successful even if the PCs belong to the same network. Finally, the usefulness of the vlan is to achieve separate the diffusion domains, making only the devices belonging to the same diffusion domain can communicate with each other. Remember to mark the correct answers as solved, because that helps other users with similar questions. I have one more question, then what us the use of this type of topology Which I uploaded at first.
Take an instance, in a company there is two departments namely, Sales and Engineering. Then what's the use? If in your topology you have more than one vlan, the correct thing is to configure the links that connect the switches in trunk mode. That prevents the packets from being re-tagged and achieves the purpose of the vlan, that is, that the packets are only retransmitted to the ports with the same vlan number configured. In order to have connectivity between PCs of different vlan, you will need a layer 3 device that does intervlan routing.
Since you are using one vlan per switch, there is no need for a trunk and the vlan id can and are different 10 and So everything works as expected. Now, if you configure 2 vlans per switch say 10 and 20 on one switch and 30 and 40 on the other than you would need a trunk and the vlan ids much match. You have 2 vlans 10 and 30 but they are both in the same subnet. So, there is no need for routing as you only have 1 subnet. Also I didn't understand much precisely like different vlan although one vlan per switch is communicating are communicating?
But in the scenario where one switch has one vlan 10 and the other has vlan 20 and one-one host is connected to it,so the vlan's communicate share data ,i don't understand that one. Is this enough to communicate VLANs? If, it is, then what is the use of different vlan? I recommend you take a look at this video. It explains trunk port, access port, routing, etc That is correct.
Your 2 vlans are in the same subnet and goes across an access port and that is why it works fine. In your current topology, if you add a third PC with the opposite vlan number, it will not be able to communicate with any PC, as the switch will not have another port through which to retransmit the packet.
To get a switch port to relay more than one vlan, you must configure both ends of the link in trunk mode. So, when the ports are access access ports, more precisely they will share single vlan information, but if more than one vlans for instance, vlan 10 on sw1 and vlan 20 on sw2, they will share info.
Buy or Renew. Find A Community. Cisco Community. Join us in congratulating October's Spotlight Award Winners! There may be a need to access different resources. Ports may be used by different departments at different times or differing levels of security may be required. Dynamic VLANs are more appropriate for these situations.
This means that as they plug into a particular port, the switch automatically configures the port for membership in the correct VLAN. Consider the case in Figure This may actually be the most common behavior for nodes connecting to a network on a particular VLAN. Once on the new network, PC4 may no longer be able to reach the correct server or may require additional configuration to support the move.
If the IP address of PC4 is statically configured, when it moves to the new location, its IP address will not match the network. It will no longer be able to reach the IP address of the gateway or the server. In this case, the node will not have any connectivity at all. However, if the switch is smart enough to recognize that PC4 has now moved to a new port, it may be able to automatically repair the connection.
Once PC4 connects to the new port, it will generate traffic. Once this has occurred, PC4 will be able to communicate just as it did before the move. The new topology would look like the one shown in Figure The node will not even have to change its IP address. But how does the switch know? As soon as the node generates a single frame, the switch completes the MAC address query and then assigns the port.
The nodes still do not have any knowledge that VLANs are used. VLAN membership can also be based on other criteria or tied to authentication schemes such as So far, the VLANs discussed have been deployed on a single switch.
How does it work? A default topology is shown in Figure where two switches have simply been powered up and several nodes connected. This also means that the connections running between the switches will also be in VLAN 1. The router provides the egress point for all nodes. In this default topology, the nodes will not have any trouble connecting to each other because the source address tables on the switches will show that they are all in the same VLAN. This will allow the unicast, multicast and broadcast traffic to flow freely.
Note also that the nodes exist on the same IP network. The connection between the switches uses either a crossover cable or an uplink port. Since the VLANs create Layer 3 boundaries around the ports connected to the hosts, they are not able to communicate. Examining Figure , there are a couple of problems. Secondly, the router is isolated from all of the nodes because it is in VLAN 1. Lastly, the switches are interconnected via different VLANs. Each of these would create communication difficulties, but taken together, there is little or no communication between network elements.
It is often the case that a switch may be full or that nodes within the same administrative unit are geographically separated from each other. In these cases, a VLAN can be extended to neighboring switches through the use of a trunk line. Trunks will be discussed in greater detail later in this chapter, but for now it is sufficient to say that trunks connecting separate switches can, among other things, convey VLAN information between network devices.
Figure suggests several changes to repair the items noted in Figure Trunk ports do not have membership in any particular VLAN. Switches in the same closet can also be interconnected via trunk lines. Generally, there are two ways to look at a trunk line. In telephony, the term trunk refers to connections between offices or distribution facilities. These connections represent an increased number of lines or time division multiplexed connections as shown in Figure Examples include 25 pair bundles or T carriers.
For data networking, trunks have little to do with increasing the number of connections between switches. The primary use of a trunk line in a data network is to convey VLAN information. The trunk line shown in Figure carries VLAN and quality of service information for the participating switch.
When a trunk line is installed, a trunking protocol is used to modify the Ethernet frames as they travel across the trunk line. In Figure the ports interconnecting the switches are trunk ports. This also means that there is more than one operational mode for switch ports. When a port is used to interconnect switches and convey VLAN information, the operation of the port is changed to a trunk.
For example, on a Cisco switch the mode command would be used to make this change. The An example of a tagged frame can be seen in Figure So, on the trunk ports, a trunking protocol is run that allows the VLAN information to be included in each frame as it travels over the trunk line.
For configuration, there are generally two steps: converting the port to trunk mode and determining the encapsulation trunking protocol to be used. There are several steps to the process in addition to host routing so Figure is labeled based on the steps listed.
PC1 sends traffic to PC2 after processing its host routing table. These nodes are in the same VLAN but they are connected to different switches. The basic process:. The original frame is forwarded to the destination port 4 based on the SAT of Switch 2. The packet shown in Figure provides detail on this modification.
In this particular case, the trunking protocol that has been used is IEEE In this case, the two computers communicating are on VLAN 2. The binary value of is shown. However, because this is a change to the actual frame, the Cyclical Redundancy Check CRC at the end of the Ethernet frame must be recalculated.
Without a trunk, the nodes will probably all be on the same VLAN which can lead to the problems noted earlier. Trunks and VLANs are a vital part of standard topologies. Of the two, IEEE The IEEE As a reminder, IEEE Switch vendors adhere to both of these standards and then add enhancements such as management. When using IEEE Per the Therefore, frame is actually changed. So, the Ethernet type, which indicates the kind of encapsulated data, must also change. As an example, IP packets have an Ethertype value of but when running over a trunk it is changed to as shown in Figure There are three ways that this information can be structured but those used in token ring and FDDI networks will not be covered here.
The 2-byte hexadecimal TCI from Figure is 20 Used in quality of service implementations, also called class of service. This is a three bit field with values ranging from 0 to 7.
The default value is 0 though vendors recommend higher values for certain types of traffic. For example, VoIP traffic is typically set to binary base 5. Figure depicts a slightly elevated priority of 2. Figure depicts prioritized traffic from another network. In this case, the priority is set to 7. This single bit field was used to indicate bit orders or flags for routing information associated with legacy protocols such as token ring and FDDI.
Today, almost all switching is Ethernet. So, the field is almost never used and the value is typically 0. This corresponds to VLAN in base 10 numbers. As this is an older Cisco proprietary protocol, not much time will be spent on its description. Figure shows an ISL tagged frame and illustrates a different approach to tagging. IEEE This also forces a recalculation of the frame CRC. ISL prepends the tag.
The ISL header is also considerably larger than the While a particular VLAN may extend well beyond a single switch and may exist throughout much of a topology, it is not necessary to have it persist on every switch. The benefits include a reduction in trunk line traffic and potential security improvement through this pruning capability, especially with static topologies.
Switch 1 prunes VLAN 3 traffic prevents passage out its trunk port. Regardless of vendor, it is always a good idea to examine the trunking configuration and determine the best approach for tagged frames and untagged frames and pruning.
Is SNMP or some other management protocol running? How will you get to all of the nodes? Are these nodes servers?
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