Information About Configuring 802.1Q Vlan Interfaces - Cisco 6000 Series Configuration Manual

Information About Configuring 802.1Q VLAN Interfaces

Information About Configuring 802.1Q VLAN Interfaces
To configure 802.1Q VLAN interfaces, you must understand the following concepts:
802.1Q VLAN Overview
A VLAN is a group of devices on one or more LANs that are configured so that they can communicate as if
they were attached to the same wire, when in fact they are located on a number of different LAN segments.
Because VLANs are based on logical instead of physical connections, they are very flexible for user and host
management, bandwidth allocation, and resource optimization.
The IEEE 802.1Q protocol standard addresses the problem of dividing large networks into smaller parts so
broadcast and multicast traffic does not consume more bandwidth than necessary. The standard also helps
provide a higher level of security between segments of internal networks.
The 802.1Q specification establishes a standard method for inserting VLAN membership information into
Ethernet frames.
Cisco IOS XR software supports VLAN subinterface configuration on 10-Gigabit Ethernet, and Fast Ethernet
interfaces.
802.1Q Tagged Frames
The IEEE 802.1Q tag-based VLAN uses an extra tag in the MAC header to identify the VLAN membership
of a frame across bridges. This tag is used for VLAN and quality of service (QoS) priority identification. The
VLANs can be created statically by manual entry or dynamically through Generic Attribute Registration
Protocol (GARP) VLAN Registration Protocol (GVRP). The VLAN ID associates a frame with a specific
VLAN and provides the information that switches must process the frame across the network. A tagged frame
is four bytes longer than an untagged frame and contains two bytes of Tag Protocol Identifier (TPID) residing
within the type and length field of the Ethernet frame and two bytes of Tag Control Information (TCI) which
starts after the source address field of the Ethernet frame.
Subinterfaces
Subinterfaces are logical interfaces created on a hardware interface. These software-defined interfaces allow
for segregation of traffic into separate logical channels on a single hardware interface as well as allowing for
better utilization of the available bandwidth on the physical interface.
Subinterfaces are distinguished from one another by adding an extension on the end of the interface name
and designation. For instance, the Ethernet subinterface 23 on the physical interface designated TenGigE
0/1/0/0 would be indicated by TenGigE 0/1/0/0.23.
Before a subinterface is allowed to pass traffic it must have a valid tagging protocol encapsulation and VLAN
identifier assigned. All Ethernet subinterfaces always default to the 802.1Q VLAN encapsulation. However,
the VLAN identifier must be explicitly defined.
Subinterface MTU
The subinterface maximum transmission unit (MTU) is inherited from the physical interface with an additional
four bytes allowed for the 802.1Q VLAN tag.
Interface and Hardware Component Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
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Configuring 802.1Q VLAN Interfaces