Advanced POWER Virtualization on IBM System p5 - Previous ...

Consider the uplinks between the switches: they carry traffic for both VLANs, 1
and 2. Thus, there has to be only one physical uplink from B to A, not one per
VLAN. The switches will not be confused and will not mix-up the different VLANs’
traffic, because packets travelling through the trunk ports over the uplink will have
been tagged appropriately.
Virtual LAN benefits
The use of VLAN technology provides more flexible network deployment over
traditional network technology. It can help overcome physical constraints of the
environment and help reduce the number of required switches, ports, adapters,
cabling, and uplinks. This simplification in physical deployment does not come for
free: the configuration of switches and hosts becomes more complex when using
VLANs. But the overall complexity is not increased; its just shifted from physical
to virtual.
VLANs also have the potential to improve network performance. By splitting up a
network into different VLANs, you also split up broadcast domains. Thus, when a
node sends a broadcast, only the nodes on the same VLAN will be interrupted by
receiving the broadcast. The reason is that normally broadcasts are not
forwarded by routers. You have to keep this in mind, if you implement VLANs and
want to use protocols that rely on broadcasting, such as BOOTP or DHCP for IP
auto-configuration.
It is also common practice to use VLANs if Gigabit Ethernet’s Jumbo Frames are
implemented in an environment, where not all nodes or switches are able to use
or compatible with Jumbo Frames. Jumbo Frames allow for a MTU size of 9000
instead of Ethernet’s default 1500. This may improve throughput and reduce
processor load on the receiving node in a heavy loaded scenario, such as
backing up files over the network.
VLANs can provide additional security by allowing an administrator to block
packets from a domain to another domain on the same switch, therefore
providing an additional control on what LAN traffic is visible to specific Ethernet
ports on the switch. Packet filters and firewalls can be placed between VLANs,
and Network Address Translation (NAT) could be implemented between VLANs.
VLANs can make the system less vulnerable to attacks.
AIX 5L virtual LAN support
Some of the technologies for implementing VLANs include:
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Port-based VLAN
Layer-2 VLAN
Policy-based VLAN
IEEE 802.1Q VLAN
Chapter 2. <strong>Virtualization</strong> technologies on System p servers 73