mohammedmahmoud Tue, 06/12/2007 - 01:32
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The best practice is that VLAN = IP subnet, although there can be work arounds to have multiple IP subnets with a single VLAN (a simple example is to use secondary IPs).

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

pccthailand Tue, 06/12/2007 - 01:38
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i don't understand how benefit to do this

ex. vlan 2 have three ip interface,,

i think one vlan should have only one ip interface

please explain me


mtechnology Tue, 06/12/2007 - 02:30
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When you want redundancy for the network.


L3 has three alternate way for the destination ,that scenario on the SVI interface

can configure three Ip ,if the link fails which has 1st ip traffic will automatically fallback to 2nd link which has secondary ip


interface Vlan1

ip address secondary

ip address

nate-miller Tue, 06/12/2007 - 09:41
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Usually the reason I've seen multiple IPs on a VLAN is IP migration or address exhaustion- if you're moving from one scheme to another, and can't touch every device at once. Let's say you're migrating from / 27 to

The old config was:

int vl 1

ip address

You would drop on this config:

int vlan 1

ip address

ip address

And now users on the old address scheme can still get to the rest of the network, until you have time to go touch their PCs and reconfigure.

You might do this when you need more IP address range within a physical cable plant, and can't accomplish this easily with downstream switches that don't support multiple VLANs or trunks, etc.


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