What will this break???

[pippin.wallace]

I am somewhat new to networking and would like to ask my network admin  to add about 30 vlans to a switch interface for convenience purposes.   Normally we get a few interfaces ether-channeled together and get three  or 4 vlans put on these interfaces, but it would sure be helpful when  standing up a new vmware esxi host to be able to reconfigure this host  at any time to work in any of our environments (currently .   What I don't know is how this kind of setup could adversely affect  things.  The thought would be that on the esxi host we would only have  3-4 vlans currently active and not even have the other 20+ even  configured on the system.  What are your thoughts in this regard.

Thank you!

[Bradley Littlejohn]

Server has vlans 1-4

switchport is configured for 1-30

The downside is that you will get flooding from the network to the server from vlans that you do not have on the server.   For example, an arp request is issued on vlan 29.  All ports in vlan 29 including trunks carrying that vlan will transmit it.  The server will see a frame with a dot1q tag with vlan 29 in it.  As long as the server drops it at the nic interface you are good.

If there is a packet storm in vlan 29,  the server will see that traffic and will be effected also.

Other than that you are solid.

[pippin.wallace]

Bradley, thank you for your reply.  I am not as concerned at the server level because most vlans will not be configured so they should be dropped, correct?  I guess my big concern would be at the switching level and affecting the entire switch fabric campus wide.  I just don't know if this would be a problem or not.

[Bradley Littlejohn]

Bradley, thank you for your reply.  I am not as concerned at the server  level because most vlans will not be configured so they should be  dropped, correct?

*** You are correct.  That is what the server SHOULD do. ****

  I guess my big concern would be at the switching  level and affecting the entire switch fabric campus wide.

*** Nope.  You are solid.  As long as the server throws away the packets with the unknown vlan IDs.****

I just don't  know if this would be a problem or not.

**** only if the server does not drop the unknown vlan IDs.   I have seen servers bridge between vlans, try to process the unknown packets and etc.... *****

Try this.  Plug your pc into a trunk port on the switch.   Your pc will then be in the native vlan.  Everything will work fine.

[pippin.wallace]

Bradley, thank you again for your assistance!

[pippin.wallace]

What would happen if I get close to maxing out my spanning-tree sessions on our

3750's with all these vlan's or is that not a serious concern with 40-50 vlan floating around?

[Bradley Littlejohn]

If you are at the limit.  That is going to be a problem.   The remain vlans will be created but, without an instance of spanning tree!  Hence, if you have dual uplinks there is nothing to block the vlans.