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Vlan name vs interface vlan ip address

Hello,

What is consider for ports to be in the same Vlan subnet, is it Vlan name or the ip address given to the SVI or the subnet advertise for that vlan on a layer 3 switch.  Like for example say have 4  layer 3 switches connected where some ports on each switch are put under vlan 802. The SVI ip address for vlan 802 is different on each switch and under eigrp advertises 802 vlan svi with there subnet. Are all those ports under 802 vlan in the same subnet because the vlan name is still 802 but the svi for each 802 vlan is different subnet just the vlan name is the same.  So that mean I have 4 subnets under vlan 802 or there all act as one subnet because the vlan name is the same?

Thanks,

1 REPLY
Hall of Fame Super Blue

It depends on how the

It's not really to do with the name or subnet. It really depends on how the switches are connected.

So in general terms for any vlan if all the switches are interconnected with -

1) access port links where each end of the link was in that vlan

or

2) trunk links where that vlan was allowed on that link

or a combination of the above then that vlan would be the same L2 broadcast domain across all your switches.

Usually it is one subnet per vlan but you can if you want use multiple subnets per vlan although if you do this generally you add secondary addressing to the one L3 SVI for that vlan and have a different SVI per switch.

However, if your switches are interconnected with - 

1) access port links where the access port is not that vlan

2) trunk links but that vlan is not allowed on that link

3) L3 routed links

then the vlan is a different vlan per switch.

From the sounds of what you are describing each switch has it's own vlan with it's own subnet and they are not the same vlan across all the switches.

Usually it is a good idea if this is the case not to reuse the same vlan number on multiple switches because it just leads to confusion.

Jon

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