SVI state depends on link state of physical ports in vlan?

thorsten.steffen · ‎09-16-2008

Hi,

commonly known the link state of a svi depends on the link state of the physical switchports which belong to this vlan.

So if there is no switchport up in this vlan the svi goes down, too.

Does anybody know where this behaviour is described in cco documentation?

Furtheron, does anybody know if only the link state of the switchports is responsible for the link state of the svi or also the stp state of the switchports.

So if there would be one switchport up left in the vlan but this switchport would be blocked, what would be the state of the svi?

This scenario of one switchport blocking in a vlan is possible for a short time period when the root port of a switch looses connectivity and the alternate port needs to change from blocked to forwarding.

Many thanks,

Thorsten

Marwan ALshawi · ‎09-16-2008

first of all

SVI state not related to physical link assignment

just make sure u enter the no shut under the svi when u creat it and u need to make sure that L2 vlan creat as well for example:

vlan 2

this creat L2 vlan

interface vlan 2

ip address 1.1.1.1 255.255.255.0

no shut

and once u enable ip rputing and u do the

show ip rpute u gonna see this SVI as a directly connected interface even if u didnt assigne it to any interface yet !!

good luck

if helpful Rate

thorsten.steffen · ‎09-16-2008

Sorry but I think your information is not correct.

Physical link state of switchports is responsible for the protocol state of a svi.

So if there is no switchport up in a vlan the associated svi also is down.

You can easily test that with any unconfigured catalyst and vlan 1. If no port is connected interface vlan 1 is down, if >=1 port is connected int vlan 1 gets up.

While I tested that some minutes ago again I found out that vlan 1 gets up not until stp is converged. So it seems that there has to be >= 1 port with link state up and with stp forwarding state to let the sci get up.

Does anybody know where this is written in cco documentation?

Best greetings

andrew.burns · ‎09-16-2008

Hi,

The feature you're referring to is called "auto-state" and is documented here:

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a0080160b14.shtml

HTH

Andrew.