Understanding Allowed Vlans; Configuring A Lan Interface As An Ethernet Access Port - Cisco nexus 5000 series Cli Configuration Manual

Configuring Access and Trunk Interfaces
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A trunk port can carry untagged packets simultaneously with the 802.1Q tagged packets. When you
assign a default port VLAN ID to the trunk port, all untagged traffic travels on the default port VLAN
ID for the trunk port, and all untagged traffic is assumed to belong to this VLAN. This VLAN is referred
to as the native VLAN ID for a trunk port. The native VLAN ID is the VLAN that carries untagged traffic
on trunk ports.
The trunk port sends an egressing packet with a VLAN that is equal to the default port VLAN ID as
untagged; all the other egressing packets are tagged by the trunk port. If you do not configure a native
VLAN ID, the trunk port uses the default VLAN.

Understanding Allowed VLANs

By default, a trunk port sends traffic to and receives traffic from all VLANs. All VLAN IDs are allowed
on each trunk. However, you can remove VLANs from this inclusive list to prevent traffic from the
specified VLANs from passing over the trunk. You can add any specific VLANs later that you may want
the trunk to carry traffic for back to the list.
To partition spanning tree protocol (STP) topology for the default VLAN, you can remove VLAN1 from
the list of allowed VLANs. Otherwise, VLAN1, which is enabled on all ports by default, will have a very
big STP topology, which can result in problems during STP convergence. When you remove VLAN1,
all data traffic for VLAN1 on this port is blocked, but the control traffic continues to move on the port.
Configuring Access and Trunk Interfaces
This section includes the following topics:
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Configuring a LAN Interface as an Ethernet Access Port

You can configure an Ethernet port as an access port. An access port transmits packets on only one,
untagged VLAN. You specify which VLAN traffic that the interface carries. If you do not specify a
VLAN for an access port, the interface carries traffic only on the default VLAN. The default VLAN is
VLAN1.
The VLAN must exist before you can specify that VLAN as an access VLAN. The system shuts down
an access port that is assigned to an access VLAN that does not exist.
To configure an Ethernet access port, perform this task:
Command
Step 1
switch# configure terminal
Step 2
switch(config)# interface {{type
slot/port} | {port-channel number}}
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
1-4
Configuring a LAN Interface as an Ethernet Access Port, page 1-4
Configuring Access Host Ports, page 1-5
Configuring Trunk Ports, page 1-6
Configuring the Native VLAN for 802.1Q Trunking Ports, page 1-6
Configuring the Allowed VLANs for Trunking Ports, page 1-7
Chapter 1 Configuring Access and Trunk Interfaces
Purpose
Enters configuration mode.
Specifies an interface to configure, and enters interface
configuration mode.
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