Using A Loopback Interface For The Wireless Functions - D-Link DWS-3024 User Manual

Some phone system require placement of a call server on the same subnet as the phones. The
D-Link tunneling feature supports this configuration.
There are a few things to consider when planning a network with L3 roaming capabilities:
• Packets that use the L3 tunnel have an extra 20 bytes in the header for encapsulation.
• To support these larger frames, you can increase the MTU size on all intermediate ports
and Unified Switch ports.
• If you use tunneling only for IP telephony, or if you set the MTU size on all wireless
clients that use tunneling to 1480, you do not need to increase the MTU size in the
network.
• For traffic in the L3 tunnel, the switch forwards IPv4 unicast frames in hardware; other
types of traffic, such as multicast and non-IP traffic, are forwarded in software.
- Multicast and non-IP traffic on the L3 tunneling network could cause network
congestion.
- Wireless tunneling does not work if IPv6 or multicast traffic is enabled on the L3
tunnel interface.
• All devices that use the L3 tunnel network are stored in the ARP cache because the
wireless subnet is local to the switch, which means the ARP cache can fill up faster than
expected.
• When tunneled clients are used in conjunction with peer switches, one of the peer switches
must be configured as a default gateway for the tunneled clients. Normally the default
gateway routes all traffic from the client's subnet to other subnets, however in a peer
switch network the Unified Switch that manages the AP to which the client is associated
routes the frames into the remote subnets. This means that each peer switch must have
routing table entries that enable it to route frames to every subnet in the network.

Using a Loopback Interface for the Wireless Functions

By creating a loopback interface, you can control which routing interface the wireless function
uses for its IP address when multiple routing interfaces exist. With the loopback interface, the
IP address of the wireless function is always the same.
In this context, the loopback interface does not refer to the loopback interface
NOTE:
with the 127.0.0.1 IP address. When you configure a loopback interface for
the wireless interface on the switch, it is essentially a permanent logical inter-
face and cannot have an IP address of 127.0.0.1. You must create a dedicated
subnet for the loopback interface, and other devices on the network must be
able to contact the IP address of the loopback interface.
You must create static routes so other devices can find the loopback interface.
The advantage of defining a loopback interface is that the interface never goes down. The
disadvantage is that network configuration is more complex because the loopback interface is
located on its own subnet and the rest of the network must know how to get to the subnet.
The network must have routes between the Unified Switch and the APs to manage. The APs
must be able to ping the IP address of the loopback interface used as the WLAN interface on
the Unified Switch.
The following procedures show an example of how to enable routing and configure an IP
address on a loopback or routing interface.
Configuring the WLAN and Tunnel Interfaces
L3 Roaming Example
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