Vlans; Notes About Vlans On Ibm Bladecenter 4-Port Gb Ethernet Switch Module; Ieee 802.1Q Vlans - IBM BladeCenter Installation And User Manual

Improper configuration of the switch module external ports or improper cabling of
the external ports to another switch device can create duplicate links that might
cause network loops. Consult your network administrator for details about the
configuration requirements for your system.
For additional information about the STP, see Appendix D, "Understanding and
troubleshooting the Spanning Tree Protocol" on page 121.

VLANs

A virtual local area network (VLAN) is a network topology configured according to a
logical scheme rather than the physical layout. VLANs can be used to combine any
collection of blade servers into an autonomous user group that appears as a group
within one or more chassis. VLANs also logically segment the blade servers into
different broadcast domains so that packets are forwarded only between blade
servers and the four external ports within the VLAN. Typically, a VLAN corresponds
to a particular subnet, although not necessarily.
VLANs can enhance performance by conserving bandwidth and improve security by
limiting traffic to specific domains.
Notes about VLANs on IBM BladeCenter 4-port Gb Ethernet switch
module
No matter what basis is used to uniquely identify blade servers and assign these
nodes VLAN membership, packets cannot cross VLANs without a network device
performing a routing function between the VLANs.
The switch supports only IEEE 802.1Q VLANs. The port untagging function can be
used to remove the 802.1Q tag from packet headers to maintain compatibility with
devices that are tag-unaware.
The switch default is to assign all blade servers and the four external ports to a
single 802.1Q VLAN named DEFAULT_VLAN.
The DEFAULT_VLAN has a VLAN ID (VID) of 1.
The Ethernet switch module can be configured to enable a wide variety of VLAN
configurations among the various external ports.

IEEE 802.1Q VLANs

The following terms are relevant to VLANs and important with respect to
understanding how VLANs function:
Tagging
Untagging
Ingress port
Egress port
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IBM BladeCenter 4-Port Gb Ethernet Switch Module: Installation and User's Guide
The act of putting 802.1Q VLAN information into the header of a packet.
The act of stripping 802.1Q VLAN information out of the packet header.
A port on a switch where packets are flowing into the switch and where
VLAN decisions must be made.
A port on a switch where packets are flowing out of the switch, either to
another switch or to an end station, and where tagging decisions must be
made.