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Explain InterVLAN Routing?

InterVLAN routing is one of major concepts that should be understood in order to understand the working of VLANs. For all the devices lying within a VLAN, Layer 3 routing is not required for communicating with one another. On the other hand, the devices that are located in separate VLANs, a layer 3 routing device is compulsorily required for communication.

For example:
Consider two VLANs: VLAN 1 and VLAN 2. There are 2 devices namely A and B in VLAN 1 and two devices C and D in VLAN 2. Here, communication between A and B does not requires a router since they are within the same VLAN i.e., VLAN 1. Similarly the devices C and D can communicate without layer 3 routing in the same VLAN 2, whereas devices A and B cannot communicate with C and D because they both are in separate networks. In this case, a layer 3 routing device is required. This type of routing i.e., routing from one VLAN to other is termed as the InterVLAN routing.

InterVLAN Routing Process

– VLAN is a security tactic used quite often for increasing the security level and reducing the number of network broadcasts.
– InterVLAN lets one VLAN take advantage of the services offered by the other one.
– The hosts in the same VLAN are connected through a trunk.
– In order to make a connection with the other VLAN, a layer 3 switch is required with routing capabilities.
– There are other solutions to this problem but InterVLAN routing is the best.
– It is the most fast, cost efficient and reliable routing solution.
– It makes use of the switches with latest technology.
– The layer 3 switches have the routing capabilities built into them.
– This is what that cut downs their cost.
– These switches act as the core switches connecting the other branch switches at one point.
– This results in a super-fast network because of the use of fast Ethernet links or super fast fiber gigabit links.
– It should be noted that these switches have certain software requirements concerning the IOS image such as:
1. EMI or enhanced multi – layer image
2. SMI or standard multi – layer image

– Before using a switch, it should be confirmed IP routing is supported.
– The layer 3 switch has two virtual interfaces one belonging to each VLAN.
– Each interface has an associated IP address ensuring that there exists a logical interface between both the networks.
– To enable this service, one last thing to be done is to give the ‘IP routing’ command.
– The way the switches and interfaces are configured is specific to the VLAN.
– This only makes the InterVLAN routing possible.
– Each of the VLANs is then assigned an interface through which direct communication can be established with the other interfaces that have been assigned to the same VLAN.
– Another major concept of InterVLAN routing is the access list.
– This list is implemented as a packet filter and it restricts the access to the hosts as well as services as required.
– The services as well as the central file servers are placed in the particular VLAN to which they belong.
– This secures them from all the potential attacks and at the same time keeping a control on their access.
– An initial scan is performed by most of the viruses and Trojans before they attack it.
– Therefore, in order to avoid the detection of a live host the ICMP echoes can be disabled by the network administrator.
– InterVLAN is quite a complicated service and also a large network cannot survive without it.

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