Dell PowerConnect 7048P - What Are Tunnel Interfaces; Why Are Routing Interfaces Needed

Configuring Routing Interfaces 845
What Are Tunnel Interfaces?
Tunnels are a mechanism for transporting a packet across a network so that it
can be evaluated at a remote location or
tunnel endpoint . The tunnel,
effectively, hides the packet from the network used to transport the packet to
the endpoint. This allows for the transmission of packets that the transport
network cannot process directly, such as in one of the following cases:
• The packet protocol is not supported.
• The packet is in an incompatible addressing space.
• The packet is encrypted.
PowerConnect 7000 Series switches support tunnels to encapsulate IPv6
traffic in IPv4 tunnels to provide functionality to facilitate the transition of
IPv4 networks to IPv6 networks.
The switch supports two types of tunnels: configured (6-in-4) and automatic
(6-to-4). Configured tunnels have an explicit configured endpoint and are
considered to be point-to-point interfaces. Automatic tunnels determine the
endpoint of the tunnel from the destination address of packets routed into
the tunnel. These tunnels correspond to Non-Broadcast Multi-Access
(NBMA) interfaces. A configured tunnel interface has a single tunnel
associated with it, while an automatic tunnel interface has an infinite number
of tunnels (limited only by the address encoding scheme).
Because tunnels are used as logical interfaces, you can define static routes
that reference the tunnels. Additionally, dynamic routing can be configured to
use the tunnels.
Why Are Routing Interfaces Needed?
The routing interfaces this chapter describes have very different applications
and uses, as this section describes. If you use the switch as a layer 2 device
that handles switching only, routing interface configuration is not required.
When the switch is used as a layer 2 device, it typically connects to an
external layer 3 device that handles the routing functions.
VLAN Routing
VLAN routing is required when the switch is used as a layer 3 device. VLAN
routing must be configured to allow the switch to forward IP traffic between
subnets and allow hosts in different networks to communicate.