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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 9 Configuring Interface Characteristics
Understanding Interface Types
Note When you put an interface that is in Layer 3 mode into Layer 2 mode, the previous configuration
information related to the affected interface might be lost, and the interface is returned to its default
configuration.
For detailed information about configuring access port and trunk port characteristics, see Chapter 11,
“Configuring VLANs.” For more information about tunnel ports, see Chapter 13, “Configuring IEEE
802.1Q and Layer 2 Protocol Tunneling.”
UNI and NNI Ports
User-network interfaces (UNIs) and network node interfaces (NNIs) are supported on the Cisco ME
switch. UNIs are typically connected to a host, such as a PC or a Cisco IP phone. NNIs are typically
connected to a router or to another switch. By default, the 10/100 ports on the Cisco ME switch are
configured as UNIs, and the SFP module uplink ports are configured as NNIs.
The default status for a UNI is administratively down to prevent unauthorized users from gaining access
to other ports as you configure the switch. Traffic is not switched between UNIs, and all arriving traffic
at UNIs must leave on NNIs to prevent a user from gaining access to another user’s private network. If
it is appropriate for two or more UNIs to exchange traffic within the switch, the UNI can be assigned to
a community VLAN. See Chapter 11, “Configuring VLANs,” for instructions on how to configure
community VLANs.
Note The exception to UNI default behavior is with IEEE 802.1Q tunneled traffic. A user can have multiple
connections to a single switch by using IEEE 802.1Q tunneling, and the UNIs on the switch do not block
the traffic by default.
Even though the default state for a UNI is shutdown, entering the default interface <interface-id>
command changes the port to the enabled state.
The default status for an NNI is administratively up to allow a service provider remote access to the
switch during initial configuration.
A port can be reconfigured from UNI to NNI and the reverse. When a port is reconfigured as another
interface type, it inherits all the characteristics of that interface type. At any time, all ports on the Cisco
ME switch are either UNI or NNI.
Access Ports
An access port belongs to and carries the traffic of only one VLAN. Traffic is received and sent in native
formats with no VLAN tagging. Traffic arriving on an access port is assumed to belong to the VLAN
assigned to the port. If an access port receives an IEEE 802.1Q tagged packet, the packet is dropped, and
the source address is not learned. IEEE 802.1x can also be used for VLAN assignment.
Two types of access ports are supported:
• Static access ports are manually assigned to a VLAN.
• VLAN membership of dynamic access ports is learned through incoming packets. By default, a
dynamic access port is a member of no VLAN, and forwarding to and from the port is enabled only
when the VLAN membership of the port is discovered. UNIs begin forwarding packets as soon as
