SVI best practice

Unanswered Question
Sep 26th, 2009

Hi,

I know that we an SVI can be 'up' with either an access or a trunk port allowing the related VLAN.

Lets say on Switch 1 we have a routed port on a switch (subnet x.x.x.x), an SVI (subnet y.y.y.y/24) and two trunks connected to different switches (Switch 2 and Switch 3) which are in turn connected to different routers.

These far end routers are in the same subnet y.y.y.y/29 and want a next hop to reach x.x.x.x, hence the SVI.

The question is should an SVI have an access switchport associated with it (with a hard loop or a couple of ports connected together) or is it okay to leave it with just Trunk interfaces.

Will there be any difference in the overall routing behaviour/processing.

I am seeing abnormal CPU utilization with an approach where no access interface is associated with the SVI in Switch 1.

Cheers

~sultan

I have this problem too.
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Giuseppe Larosa Sun, 09/27/2009 - 04:32

Hello Sultan,

>> The question is should an SVI have an access switchport associated with it (with a hard loop or a couple of ports connected together) or is it okay to leave it with just Trunk interfaces.

No, autostate feature relates the SVI state to the existance of a L2 port in STP forwarding state for the corresponding L2 vlan broadcast domain.

An access port in vlan X is not needed to have the SVI to work.

Further note:

>> with a hard loop or a couple of ports connected together

not recommended.

try to understand what are the reasons for this high CPU usage:

use

sh proc cpu sorted 1min

to see what processes are using most resources.

What platform and IOS version is involved?

traffic is only unicast or also multicast?

Hope to help

Giuseppe

sultan-shaikh Sun, 09/27/2009 - 15:04

Hello Giuseppe,

Thanks for your response.

Traffic is majorly multicast, I will be doing some checks today and try to understand this more.

Cheers

~sultan

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