User guide

E
XTREME
W
ARE
S
OFTWARE
U
SER
G
UIDE
11-13
VLAN A
GGREGATION
VLAN A
GGREGATION
P
ROPERTIES
VLAN aggregation is a very specific application, and the following properties apply to
its operation:
• All broadcast and unknown traffic remains local to the sub-VLAN and does not
cross the sub-VLAN boundary. All traffic within the sub-VLAN is switched by the
sub-VLAN, allowing traffic separation between sub-VLANs (while using the same
default router address among the sub-VLANs).
• Hosts are located on the sub-VLAN. Each host can assume any IP address within the
address range of the super-VLAN router interface. Hosts on the sub-VLAN are
expected to have the same network mask as the super-VLAN, and have their default
router set to the IP address or the super-VLAN.
• All traffic (IP unicast and IP multicast) between sub-VLANs is routed through the
super-VLAN. For example, no ICMP redirects are generated for traffic between
sub-VLANs, because the super-VLAN is responsible for sub-VLAN routing. Unicast
IP traffic across the sub-VLANs is facilitated by the automatic addition of an ARP
entry (similar to a proxy ARP entry) when a sub-VLAN is added to a super-VLAN.
This feature can be disabled for security purposes.
• IP multicast traffic between sub-VLANs is routed when an IP multicast routing
protocol is enabled on the super-VLAN.
VLAN A
GGREGATION
L
IMITATIONS
The following limitations apply to VLAN aggregation:
• No additional routers may be located in a sub-VLAN. This feature is only applicable
for “leaves” of a network.
• A sub-VLAN cannot be a super-VLAN, and vice-versa.
• Sub-VLANs are not assigned an IP address.
• Typically, a super-VLAN has no ports associated with it, except in the case of
running ESRP.
• If a client is moved from one sub-VLAN to another, you must clear the IP ARP cache
at the client and the switch, in order to resume communication.