VLAN Interface rate stats not matching only interface

[AlexFer]

Hello experts,

I'm unable to explain the "input rate" and "output rate" of the VLAN interface on 4500x.

4500x#show vlan id 18
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
18 Redacted active Te1/6
VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
18 enet 100018 1500 - - - - - 0 0
Remote SPAN VLAN
----------------
Disabled
Primary Secondary Type Ports
------- --------- ----------------- ------------------------------------------

4500x#show interfaces vlan 18
Vlan18 is up, line protocol is up
Hardware is Ethernet SVI, address is c067.WWW.XXX (bia c067.WWW.XXX)
Internet address is 10.100.100.18/29
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not supported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 2000 bits/sec, 3 packets/sec
L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
L3 out Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
IPv6 L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
IPv6 L3 out Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
0 packets input, 0 bytes, 0 no buffer
Received 18522748 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
1058519159 packets output, 1121908759007 bytes, 0 underruns
0 output errors, 2 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out

4500x#show interfaces Te1/6
TenGigabitEthernet1/6 is up, line protocol is up (connected)
Hardware is Ten Gigabit Ethernet Port, address is c067.YYY.ZZZ (bia c067.YYY.ZZZ)
MTU 1500 bytes, BW 10000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 11/255, rxload 2/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 10Gb/s, link type is auto, media type is 10GBase-SR-*
input flow-control is on, output flow-control is on
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 82254000 bits/sec, 27882 packets/sec
5 minute output rate 451144000 bits/sec, 47915 packets/sec
1332715128595 packets input, 527560088774965 bytes, 0 no buffer
Received 62145249 broadcasts (62113829 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
2200306539061 packets output, 2500240903432260 bytes, 0 underruns
0 output errors, 0 collisions, 3 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out

Since Te1/6 is the only interface, it would not be processing much L2 user traffic, so I'm expecting VLAN interface's Layer 3 "5 minute input rate" and "5 minute output rate" to match physical interface's Layer 2 & 3 "5 minute input rate" and "5 minute output rate" but it doesn't. In fact, occasionally, the former pair are both 0.

What am I misunderstanding about the rate counters?

R's, Alex

PS. Te1/6 isn't a routed interface due to legacy.

[Giuseppe Larosa]

Hello Alex,

SVI counters accuracy is platform dependent and also sometimes IOS version dependent.

You just need to take in account this behaviour and because only one interface is associated to the Vlan it is easy for you to monitor the traffic over it (the physical interface).

Edit:

You can easily guess SVI counters are not accurate by looking at the lines below ,  these counters cannot be zero !

L3 in Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes
L3 out Switched: ucast: 0 pkt, 0 bytes - mcast: 0 pkt, 0 bytes

Hope to help

Giuseppe

[AlexFer]

HI Giuseppe,
thanks for prompt reply.

> SVI counters accuracy is platform dependent and also sometimes IOS version dependent.

I don't understand what this means. I have plenty of other switches without this rate (and counters) anomaly. If 4500x is different, why would it be?

R's, Alex

[Giuseppe Larosa · Accepted solution]

Hello Alex,

on C4500x it depends on the model of supervisor you have on chassis.

>>

> SVI counters accuracy is platform dependent and also sometimes IOS version dependent.

I don't understand what this means. I have plenty of other switches without this rate (and counters) anomaly. If 4500x is different, why would it be?

It is a question of hardware implementation I guess and how it interacts with software. I have simply reported what I have seen on the field. For some switch models these counters work for other ones  do not.

By the way, how many times have you seen last input never or weeks ago on a physical interface alive with traffic over it in both directions?

Just to make an example of another strange behaviour and this happens also on C6500 devices.

Hope to help

Giuseppe