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

Typically, a VLAN is a single broadcast domain that enables all nodes in the
VLAN to communicate with each other without any routing (L3 forwarding) or
inter-VLAN bridging (L2 forwarding). For TCP/IP, this means that all node’s
interfaces in the same VLAN typically share the same IP subnet/netmask and
can resolve all IP addresses on this VLAN to MAC addresses by using the
Address Resolution Protocol (ARP). Even if a VLAN spans multiple switches,
from the TCP/IP point-of-view, all nodes on the same VLAN can be reached with
a single hop. This is in contrast to communication with nodes in other VLANs:
their IP addresses cannot (and need not) be resolved by ARP, because these
nodes are reached by making an additional hop through an L3 router (which
UNIX administrators sometimes refer to as a gateway).
In Figure 2-14 on page 72, two VLANs (VLAN 1 and 2) are defined on three
switches (Switch A, B, and C). There are seven hosts (A-1, A-2, B-1, B-2, B-3,
C-1, and C-2) connected to the three switches. The physical network topology of
the LAN forms a tree, which is typical for a non-redundant LAN:
► Switch A
– Node A-1
– Node A-2
– Switch B
• Node B-1
• Node B-2
• Node B-3
– Switch C
• Node C-1
• Node C-2
In many situations, the physical network topology has to take into account the
physical constraints of the environment, such as rooms, walls, floors, buildings,
and campuses, to name a few. But VLANs can be independent of the physical
topology:
► VLAN 1
– Node A-1
– Node B-1
– Node B-2
– Node C-1
Chapter 2. <strong>Virtualization</strong> technologies on System p servers 71