Intel 480T, User Manual

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C H A P T E R 1 0 IP Unicast Routing
• 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 Aggregation Limitations
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.
Isolation Option for Communication Between
Sub-VLANs
To facilitate communication between sub-VLANs, by default, an
entry is made in the IP ARP table of the super-VLAN that performs
a proxy ARP function. This allows clients on one sub-VLAN to
communicate with clients on another sub-VLAN. In certain
circumstances, intra-sub-VLAN communication may not be desired
for isolation reasons. To prevent normal communication between
sub-VLANs, disable the automatic addition of the IP ARP entries
on the super-VLAN, using the command:
disable subvlan-proxy-arp vlan <super-vlan name>
The isolation option works for normal, dynamic, ARP-based client
communication.