Month: September 2012

Routing between VLANs

The VLAN hosts reside in their own broadcast domain and can interact /communicate quite freely. VLANs can build partition of network as well as separation of traffic at layer 2 of the OSI, and as we have discussed earlier about the need of routers, in order to host or if you want any other device to interact between VLANs, then it is essential to use layer-3 device.

The division of the LAN into multiple VLAN is basically the same like separating them into different physical LANs. In this case is clear that you will need a router if you want to go from one LAN to another.

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Trunking Methods – VLAN Identification methods across multiple switches

Frame Tagging

It is possible to build VLANs to pair number of connected switches. In the figure below you can see that the hosts from different VLANs are spread throughout number of switches. The biggest advantage to implement VLANs is its flexible and power-packed nature. The drawback is that it can become complicated—also for a switch— so it is important to have a way through which keeping the track of each one is easy i.e. all the users and frames when they travel the VLANs  and switch fabric. (Switch fabric is actually referred to as a group of switches that shares the same information of VLAN.)

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ISL Inter-Switch Link Protocol – Trunking or Frame Tagging protocol

Inter-Switch Link (ISL) is specifically used for tagging information of VLAN onto an Ethernet frame. This tagging information permits multiplexing of VLANs over a trunk link and this takes place through an external covering procedure or method, as a result of which the switch can easily determine/identify the membership of VLAN frame over the trunked link. When you run ISL, then it is easy to interconnect number of switches and it is also possible to maintain the information of VLAN while the traffic is passing on trunk links between switches.

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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:

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Static vs Dynamic VLANs

All About VLAN Memberships

The administrator create LANs and also assign switch ports to every VLAN. This type of VLAN is referred to as static VLAN . If the administrator is ready to put little more effort then he can assign hardware addresses to all the host devices in a database, in order to assign VLANs vitally the switches can be configured every time a host is connected/plugged into a switch.  

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