SVI utilization

[glen.grant]

     We have some 6509's in a datacenter for a large customer .  We use a tool called Vitalnet to get statistics on ports etc.  What we are are seeing is the tool says it is seeing above 100% utilization on SVI interfaces.  These interfaces have 1 gig  as the parameter .I always thought the parameter was just used for routing decisions etc .   So I assume  the SVI is running above 1 gig at times .  The box has a mixture of 60% CFC cards and maybe 40%  DFC cards installed .  I guess the question is , is it a problem if the SVI is running above 1 gig ?   For the most part we have not had any issues with the boxes and if you look at the fabric itself  there is nothing running above 2% .  We are currently looking at an issue with slow SAP complaints (who isn't?)  so hence the questions.  I have looked at a lot of things ,  spanning tree roots are in the right place and match up to the hsrp active side of things etc...  Why traffic is getting punted to the SVI I'm not sure though. There is no acl's or logging on any of these SVI's .  They do have multicast turned on for the servers .  This is a datacenter with all servers attached .  Insights ?

[Joseph W. Doherty · Accepted solution]

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Posting

A SVI throughput is the aggregate of all the ports, on that device, in the SVI transiting L3.  So depending on those ports, usage can go above gig, even way, way above.

Traffic to the SVI isn't "punted", again, it's the aggregate using that logical L3 interface for the correspond VLAN.

For example, traffic between two hosts, on two ports, but in the same VLAN, won't register on the SVI.  However, if those host ports are in two different VLANs, port 2, VLAN 20, ingress traffic will count as SVI 10 egress traffic.  If such traffic is going to VLAN port 3, VLAN 30, SVI will count it as ingress traffic, while the port will count it as egress traffic.

How high the SVI is running shouldn't matter.  Overall load on the 6500, may.  Also, L3 traffic between two ports shouldn't load the 6500 much differently from L3 traffic between two ports.

[glen.grant]

  Thanks Joseph for the great explanation .  That was my general understanding and your explanation certainly cleared everything up.  You know of  course everyone who doesn't get networking looks at a report that indicates a level that says 180% of the SVI bandwidth and they go off the deep end  and you end up having to explain it . Thanks again.