Packet Transmission - Part 1 of 2
In this video, I'm going to talk about the different ways in which one can forward packets that are transmitted over the air into the backend network. And I'm going to cover some diverse aspects here. How packets from different wireless SSIDs can be put on different VLANs or GRE tunnels and also how mobility's handled from an IP perspective. So we're going to talk about mobility within a particular controller-domain and also mobility across controller-domains. So to begin with, it is important to understand how SSIDs which are the wireless services to which users connect can be mapped to a back-end network. And very briefly, the idea is as follows. And I'm going to draw first a logical picture of the Meru wireless LAN.
There is a controller, and the controller connects to access points which may be either local or remote through either layer 2 or layer 3. Now, access points establish layer 2 or layer 3 tunnels between themselves and the controller, and the data packets from clients are transmitted back and forth within this tunnel. The controller is the central point to which all the wireless packets come in, and when the packets come into the controller they can be put on multiple VLANs depending upon policy mapping. So when we have an SSID, which is a wireless service, the default way in which packets are mapped on from the wireless network to the wired network is by mapping an SSID to a VLAN.
A controller has multiple ports, and therefore we have VLANs mapped to either the primary or the secondary port, so it's really a combination of VLAN and port mapping. It is also possible to not just map packets to a particular VLAN, but to actually map them to a GRE tunnel so that they can be further dropped off at a different location somewhere else in the enterprise. So we're going to talk about the GRE-based tunnel mapping as a refinement of how you do VLAN mapping. But the summary is that, by default, we start by mapping an SSID to a VLAN or a GRE which in turn are mapped with specific ports.
Now, while this is the default mapping, an SSID might either be what we call in tunneled mode or in bridge mode. In a tunneled mode, all the packets that are going over the wireless network will go through the tunnel from the AP into the controller. In the controller, they'll get mapped to the VLAN or GRE. That's a standard. However, you might have situations where you have a far away AP, or let us say a home access point that might also have some tunnel traffic, but maybe it has multiple SSIDs where some traffic needs to be tunneled and other traffic is locally bridged. So on a poor SSID basis, you could either do tunneling or bridging.
Tunneling is default, but bridging allows the option of having a local drop-off corresponding to that SSID. Now what this enables, of course, from a use-case perspective is that your employees, in an enterprise, can take access points home. They plug in the access points, the access points are centrally managed by a controller, and multiple SSIDs can be applied on this access point where some SSIDs will tunnel packets all the way back into the corporate network, other SSIDs will bridge packets locally. That allows, for example, an employee to take their laptop and wireless phone home and still always remain a part of the enterprise network while the family can connect to the network and at the same time just get their packets bridged off. So this is one level of abstraction where you do tunneling or bridging.
Therefore, there is no concept of roaming at that point in terms of IP. Packets always land on the same controller, and hence they go to the same VLAN. As the client moves to a different controller-domain, these controllers are talking to each other so they figure out, and packets are piped back to the original controller and that way the client always retains his IP address.
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Meru Networks Wireless Virtualization Architecture - Part 1by merunetworks1,801 views
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