vlan assignmnet

[rakeshmole]

hi ..

Please help me with the explanation of how does a vlan map assoacisate to a ip subnet, what i mean is vlan is a group of ports/mac addresses, however how does ip segementation happen for example when i mean an assumption  vlan-5 , i assume that there is an ip range for example 192.168.5.1 to 192.168.5.254 assoasciated with it.

Where does this assosciation happen , i mean where is it defined?

Is it on the switch database ?

[vmiller]

There are some more articulate members of the community (Peter, Leo.....) that may weigh in.

starting with a port.

You assign it to a vlan. Which is defined in the the vlan database.

Then

For routing purposes, you create a swtiched virtual interface (SVI) which is the logical instance for routing that vlan, and all its members.

Consider,

Interface fastethernet 0/0

ip address 10.10.10.1/24                 This is a physical, routed interface.

interface vlan110

ip address 10.10.10.2/24                      this is an SVI (on a switch) ports defined in this vlan should be addresseed out of                                                            this subnet either by static assignment or DHCP

I'll leave it to my betters to tidy up my quick explination. Have at it gents!

[Kishore Chennupati]

Peter would give a splendid answer.  Where are you?

[darren.g]

Rakesh Nair wrote:
hi .. 
Please help me with the explanation of how does a vlan map assoacisate to a ip subnet, what i mean is vlan is a group of ports/mac addresses, however how does ip segementation happen for example when i mean an assumption  vlan-5 , i assume that there is an ip range for example 192.168.5.1 to 192.168.5.254 assoasciated with it.
Where does this assosciation happen , i mean where is it defined?
Is it on the switch database ?

A given VLAN doesn't automatically associate with an IP subnet.

A VLAN is a layer 2 instance - it is not aware of the IP protocol stack (which is layer 3).

If you want a given layer-2 VLAN to associate with a given layer-3 IP address subnet, you need to create a Switched Virtual Interface or SVI in the switch - and while this is supported for at least one VLAN on all Cisco switches, not all of them support multiple SVI's being created.

The way you associate an SVI to a given VLAN is to simply create it with the same VLAN number as your layer 2 VLAN. On a Cisco switch, you do soemthing like this

switch# configure terminal

switch(config)# vlan 100

switch(config-vlan)# name Workstations

switch(config-vlan)# exit

switch(config)# interface vlan100

switch(config-if)# description Workstation SVI

switch(config-if)# ip address 10.10.0.254 255.255.255.0

switch(config-if)# no shut

switch(config-if)# end

This will get you something like this

switch# show vlan

EQX-SY1-COR-SW1#sh vlan

VLAN Name                                   Status           Ports

---- -------------------------------- --------- -------------------------------

100    workstations                          active 

switch# show running-config interface vlan100

Building configuration...

Current configuration : 213 bytes

!

interface Vlan100

description Workstation SVI

ip address 10.10.0.254 255.255.255.0

end

You can then add individual ports into VLAN100 and have them talk to the 10.10.0.254 address. Note that the SVI interface VLAN100 will *not* come up and be active until there is an individual ACTIVE (I.E. plugged in and online) port in the layer 2 VLAN 100.

Hope this helps.

Cheers.

[Mohit Chauhan · Accepted solution]

Rakesh Nair wrote:
hi .. 
Please help me with the explanation of how does a vlan map assoacisate to a ip subnet, what i mean is vlan is a group of ports/mac addresses, however how does ip segementation happen for example when i mean an assumption  vlan-5 , i assume that there is an ip range for example 192.168.5.1 to 192.168.5.254 assoasciated with it.
Where does this assosciation happen , i mean where is it defined?
Is it on the switch database ?
Hi Rakesh,
 
 VLan is basically working at layer 2 and ip as you would know is at Layer 3.
 To understand the concept more easily, its good to look at legacy layer 2 switches. if you have a simple layer 2 switch, you would not see any Ip address on that vlan at all (except for the management, which we'll ignore here as that is not related to what we are discussing).
 So in that case, a simple vlan will not have any direct relation to the ip address except that the vlan will help to contraint the broadcast within that vlan itself. Not to confuse you, but you can have two PCs from different ip address subnet say 192.168.1.0/24 and 10.1.1.0/24.
 
 Switch doesnt understand ip packets, its just looks at the frame. so to answer your question, there is no association of ip address in a switch mac address table.
 
 As mentioned by Darren, you may have an ip addresses assigned to the SVI which happens on the Layer 3 switch. This basically allows the switch to allow routing from one vlan to another and also acts as default gateway to the clients sitting in that vlan. for eg you have a PC and you assign a static ip 192.168.1.10/24 and your gateway as 192.168.1.1. then you program the SVI on the layer 3 switch with an ip of 192.168.1.1. (the command syntax would be like mentioned by Darren above)
 
 Hope this helps- Happy to explain more if required.!

[rakeshmole]

thanks , i have got it now.

Thanks to you all....:-)