Dell FCX624-I Laptop User Manual


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470 PowerConnect B-Series FCX Configuration Guide
53-1002266-01
Configuring the same IP subnet address on multiple port-based VLANs
13
FIGURE 100 Multiple port-based VLANs with the same protocol address
Each VLAN still requires a separate virtual routing interface. However, all three VLANs now use the
same IP subnet address.
In addition to conserving IP subnet addresses, this feature allows containment of Layer 2
broadcasts to segments within an IP subnet. For ISP environments where the same IP subnet is
allocated to different customers, placing each customer in a separate VLAN allows all customers to
share the IP subnet address, while at the same time isolating them from one another Layer 2
broadcasts.
NOTE
You can provide redundancy to an IP subnet address that contains multiple VLANs using a pair of
Layer 3 Switches configured for Dell VRRP (Virtual Router Redundancy Protocol).
The Dell PowerConnect device performs proxy Address Resolution Protocol (ARP) for hosts that
want to send IP traffic to hosts in other VLANs that are sharing the same IP subnet address. If the
source and destination hosts are in the same VLAN, the Dell PowerConnect device does not need
to use ARP:
If a host attached to one VLAN sends an ARP message for the MAC address of a host in one of
the other VLANs using the same IP subnet address, the Dell PowerConnect device performs a
proxy ARP on behalf of the other host. The Dell PowerConnect device then replies to the ARP by
sending the virtual routing interface MAC address. The Dell PowerConnect device uses the
same MAC address for all virtual routing interfaces.
When the host that sent the ARP then sends a unicast packet addressed to the virtual routing
interface MAC address, the device switches the packet on Layer 3 to the destination host on
the VLAN.
VLAN 2
VLAN 3
VLAN 4
VLAN 2
VE 1
-IP 10.0.0.1/24
VLAN 3
VE 2
-Follow VE 1
VLAN 4
VE 3
-Follow VE 1
Switch