VLANs – Trunk and Access link types

The frames are actually switched all over the internetwork, it is important for the switches to keep the record of all the various kinds of frames, and also know how to utilize it on the basis of the hardware address. The management of frames is done in a different manner depending on the kind of link they are passing through.

In the switched environment there are two various kinds of links access and trunk links:

Access links This link is referred to as as the native VLAN of the port as it is part of one VLAN only. When any device is connected to an access link then it is not aware of a VLAN membership—the device does not understand about the physical network and so it just presumes that it’s a component of a broadcast domain. All the information of VLAN is actually removed by switches from the frame before it reaches to an access-link device. No communication or interaction can take place between the Access-link devices  and the devices outside their VLAN, the communciation is possible only when the packet is routed through a router.

Trunk links The term trunks is named after the telephone system trunks that carry number of conversations. Similarly, the trunk links can carry/move multiple VLANs. There is a fixed trunk link i.e. 100- or 1000Mbps between a switch and a router, between two switches or between a server and a switch. At one time these can carry the traffic of as many as 1 to 1005 VLAN. It is not possible to run them on links of 10Mbps. Trunking permits to make one port part of many VLANs simultaneously. This can be really beneficial. In other words, you can easily arrange things up to a server in 2 broadcast domains at the same time, and it would be easy for the user to log in and access it without crossing a layer-3 device (router). There is one more advantage to trunking when you are attaching switches. Trunk link carries little or all information of VLAN across the link, but if the switches are not trunked then the VLAN 1 information will be carried across the link and this will happen by default. Due to this reason the configuration of all VLANs is done on a trunked link unless it is deleted by an administrator manually. In the figure you can see the utilization of various links in a switched network. It is the trunk link between the two switches that makes the communication possible to all VLANs. On the contrary, when you use an access link then it permits the use of single VLAN between switches. Here you can easily notice that these hosts are making use of access links in order to link to the switch, which means that they can only communicate in single VLAN.

Trunk link

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