Multiple ip interface for vlan

[pccthailand]

Hi

I have some confuse about vlan

Can one vlan have more subnet or more ip address ?

thanks

[mohammedmahmoud]

Hi,

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]

Hi

i don't understand how benefit to do this

ex. vlan 2 have three ip interface 192.168.1.254, 192.168.2.254, 192.168.3.254

i think one vlan should have only one ip interface

please explain me

Thanks

[mtechnology]

When you want redundancy for the network.

example:

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 192.168.1.254 255.255.255.0 secondary

ip address 192.168.2.254 255.255.255.0

[nate-miller]

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 1.1.1.0 / 27 to 2.2.2.0/24.

The old config was:

int vl 1

ip address 1.1.1.1 255.255.255.224

You would drop on this config:

int vlan 1

ip address 2.2.2.1 255.255.255.0

ip address 1.1.1.1 255.255.255.224

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.

[pccthailand]

thanks for all comment :)

[salmanansari6969]

can i assign Multiple ip's to one single Vlan such as Configure VLAN10 with Ip's 192.168.1.0/30, 192.168.2.0/30, 192.168.3.0/30.

[Joseph W. Doherty]

Yes you can, using secondary addresses, as shown in mtechnology's post.  NB: there are some issues in doing this, such, as by default, DHCP will only provide addresses to the primary address network.

[obashford]

If we add the secondary address scope and default router  to the dhcp server why would it not work? 

[Joseph W. Doherty]

---

@obashford wrote:

If we add the secondary address scope and default router  to the dhcp server why would it not work? 

---

Unclear why you're asking about a default router, but the fundamental problem with hosts on secondary subnets, if the host is looking for its initial IP, how would the router forwarding the DHCP request "know" what subnet the host wants to use?

Conversely, if the DHCP server "knows" what the primary subnet is and what all the secondary subnets are, how does it know what subnet to provide to the host beyond the first available subnet IP it finds, perhaps defaulting with the primary subnet and the secondary subnets in some sequence?