What do SVI statistics really show?

[gkuzmowycz]

For an SVI on a Cat 4507, what do the interface stats, like "5 minute input rate" and "5 minute output rate" actually count? What is "input" and "output" from the SVI's perspective?

[Jon Marshall]

Any traffic that has been routed between vlans.

If the traffic is local to the same vlan then there is no need for the SVI to be involved. Only when a host on one vlan wants to communicate with a host on another vlan are packets transmitted via the SVI.

Jon

[Edison Ortiz]

Jon,

Based on a brief test in the lab, not all traffic gets punted to the SVI, most of the traffic is Layer3 switched.

Here is the topology:

R1(Vlan2)<->Switch1<->(Vlan3)R3

Switch#clear counter

Clear "show interface" counters on all interfaces [confirm]

!

Switch#sh int vlan 3 | i packets input|packets output

0 packets input, 0 bytes, 0 no buffer

0 packets output, 0 bytes, 0 underruns

!

Switch#sh int vlan 2 | i packets input|packets output

0 packets input, 0 bytes, 0 no buffer

0 packets output, 0 bytes, 0 underruns

!

!

R3#ping 10.1.1.1 repeat 1000000

Type escape sequence to abort.

Sending 1000000, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!

!

!

Switch#sh int vlan 3 | i packets input|packets output

0 packets input, 0 bytes, 0 no buffer

0 packets output, 0 bytes, 0 underruns

Switch#sh int vlan 2 | i packets input|packets output

0 packets input, 0 bytes, 0 no buffer

0 packets output, 0 bytes, 0 underruns

Switch#sh int vlan 3 | i packets input|packets output

0 packets input, 0 bytes, 0 no buffer

0 packets output, 0 bytes, 0 underruns

Switch#sh int vlan 2 | i packets input|packets output

0 packets input, 0 bytes, 0 no buffer

0 packets output, 0 bytes, 0 underruns

Switch#sh int vlan 3 | i packets input|packets output

0 packets input, 0 bytes, 0 no buffer

0 packets output, 0 bytes, 0 underruns

_______

Here are the ip addresses of the routers directly connected to the switch:

Switch#sh ip cef 10.1.1.1

10.1.1.1/32

attached to Vlan2

Switch#sh ip cef 10.3.3.1

10.3.3.1/32

attached to Vlan3

HTH,

__

Edison.

[gkuzmowycz]

Thanks, Edison, very informative. So those counters just count process-switched packets? Is there any way, internal to the switch, of counting all the routed traffic?

[Edison Ortiz]

Sure, deploy NetFlow:

http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/31sga/configuration/guide/nfswitch.html

HTH,

__

Edison.

[gkuzmowycz]

That costs money on the 4500 series.

[Jon Marshall]

Edison

I need to get another job i think then i can setup another lab :)

Many thanks for that.

Jon

[lamav]

Edison:

Im not sure I get it....

So, the packet enters the switch from the router on the physical layer 2 interface....and then....what?

It is cef switched? So the packet's next hop and output interface are ascertained from the cef and adjacency tables that are located on the....switch card? Switch port (dCEF)? Am I getting this right?

HELP! :-)

Thanks

Victor

[Edison Ortiz]

So, the packet enters the switch from the router on the physical layer 2 interface....and then....what?

It goes out via another physical layer 2 interface on the same switch.

Also, during my test, I tried to run the inter-vlan between multiple switches and that's where I noticed the SVI counters increasing. I ran out of time so I didn't dig deeper.

Today isn't possible for me to duplicate once again but that's the idea. BTW, my test was done in 3550s - no switch modules (dCEF).

__

Edison.