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9-2
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-06
Chapter 9 Configuring Interfaces
Understanding Interface Types
UNI, NNI, and ENI Port Types
The Cisco ME switch supports user-network interfaces (UNIs), network node interfaces (NNIs), and
enhanced network interfaces (ENIs). 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. ENIs have the same functionality
as UNIs, but can be configured to support protocol control packets for Cisco Discovery Protocol (CDP),
Spanning-Tree Protocol (STP), Link Layer Discovery Protocol (LLDP), and EtherChannel Link
Aggregation Control Protocol (LACP) or Port Aggregation Protocol (PAgP). By default, the 10/100 ports
and the dual-purpose ports on Cisco ME 3400-12CS and ME 3400-2CS switches are configured as UNIs,
and the SFP-only module uplink ports are configured as NNIs. You must configure ports to be ENIs; no
ports are ENIs by default.
If the switch is running the metro base or metro access image, only four ports on the switch can be
configured as NNIs at one time, but all ports on the switch can be configured as UNIs or ENIs. Starting
with Cisco IOS release 12.2(25)SEG, if the switch is running the metro IP access image, there is no limit
to the number of NNIs that can be configured on the switch.
The default state for a UNI or ENI is administratively down to prevent unauthorized users from gaining
access to other ports as you configure the switch. Traffic is not switched between these ports, and all
arriving traffic at UNIs or ENIs 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 or ENIs to exchange traffic within the
switch, the UNIs and ENIs can be assigned to a community VLAN. See
Chapter 11, “Configuring
VLANs,” for instructions on how to configure community VLANs.
Note Even though the default state for a UNI or ENI 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 or ENI and the reverse. When a port is reconfigured as
another interface type, it inherits all the characteristics of that interface type. When you reconfigure a
UNI or ENI to be an NNI, you must enable the port before it becomes active.
Changing the port type from UNI to ENI does not affect the administrative state of the port. If the UNI
status is shut down, it remains shut down when reconfigured as an ENI; if the port is in a no shutdown
state, it remains in the no shutdown state. At any time, all ports on the Cisco ME switch are either UNI,
NNI, or ENI.
Port-Based VLANs
A VLAN is a switched network that is logically segmented by function, team, or application, without
regard to the physical location of the users. For more information about VLANs, see
Chapter 11,
“Configuring VLANs.” Packets received on a port are forwarded only to ports that belong to the same
VLAN as the receiving port. Network devices in different VLANs cannot communicate with one another
without a Layer 3 device to route traffic between the VLANs.
VLAN partitions provide hard firewalls for traffic in the VLAN, and each VLAN has its own MAC
address table. A VLAN comes into existence when a local port is associated with the VLAN ID or when
a user creates te VLAN ID.