07-16-2009 08:51 AM - edited 03-04-2019 05:27 AM
I have been puzzled by this for sometime and have been trying to get to the bottom of it.
I have 2 routers connected via a 10Mb FD Ethernet link and on router 1 I am traffic shaping outbound on this link with the following config:
Policy Map SHAPE
Class class-default
Traffic Shaping
Average Rate Traffic Shaping
CIR 64000 (bps) Max. Buffers Limit 1000 (Packets)
Bc 1280 Be 0
When I flood this link I see the following on show interface f0/0:
poc#sh int f0/0 | inc 30 second
30 second input rate 0 bits/sec, 3 packets/sec
30 second output rate 64000 bits/sec, 144 packets/sec
However on the other routers interface I see:
spray#sh int f6 | inc 30 second
30 second input rate 75000 bits/sec, 148 packets/sec
30 second output rate 0 bits/sec, 0 packets/sec
So I am confused as to why interface commands show a difference in data i.e 64Kb on the outgoing interface (poc) and 75Kb on the incoming interface (spray)?
This is a back to back connection between 2 seperate routers. (poc out connected to spray in)
And what is this 9-10 bytes per packet of unaccounted traffic?
Solved! Go to Solution.
07-16-2009 09:29 AM
Hello Kate,
interface counters on ethernet interfaces consider the layer2 frame without the final 4 byte FCS so the size of frame is seen as
IP size + 14 bytes (but it cannot be less then 60 bytes because ethernet frame mimimum size is 64 bytes, 1518 bytes max including FCS)
I'm sure old CAR committed access rate works taking in account L2 overhead and I think also Class based shaping and policing do the same.
Hope to help
Giuseppe
07-16-2009 09:29 AM
Hello Kate,
interface counters on ethernet interfaces consider the layer2 frame without the final 4 byte FCS so the size of frame is seen as
IP size + 14 bytes (but it cannot be less then 60 bytes because ethernet frame mimimum size is 64 bytes, 1518 bytes max including FCS)
I'm sure old CAR committed access rate works taking in account L2 overhead and I think also Class based shaping and policing do the same.
Hope to help
Giuseppe
09-02-2011 09:43 AM
Hi Giuseppe,
Recently I have came across similar question as Kate.
We have a WAN ASR1006 Cisco router connected over Ethernet WAN interface to the remote location.
interface GigabitEthernet1/2/3
bandwidth 200000
ip address x.x.x.x 255.255.255.252
ip flow ingress
ip flow egress
logging event link-status
load-interval 30
no negotiation auto
cdp enable
service-policy output XXXXXX
end
We have a shaping policy applied to the interface as follows:
GigabitEthernet1/2/3
Service-policy output: XXXXXXX
Class-map: class-default (match-any)
329736629 packets, 261478270158 bytes
30 second offered rate 94461000 bps, drop rate 24000 bps
Match: any
Queueing
queue limit 791 packets
(queue depth/total drops/no-buffer drops) 0/85300/0
(pkts output/bytes output) 329743966/261475845041
shape (average) cir 190000000, bc 760000, be 0
target shape rate 190000000
We have a Netscout TAP on the circuit which feeds data into Corvil monitoring device.
The Corvils has been configured for 4 ms sampling (same as the Tc configured on Cisco router). The max traffic volumes reported by the Corvil are higher than 190Mbps and on avarage max traffic volumes for 4 ms sampling are around 194Mbps. And this could be explained by what you said that the router doesn't count Ethernet 4bytes FCS while it calculates Bc (commited burst size) for shaping purposes.
However few times a day I can see a spike of a 220-230Mbps, which is imposible to have on 200Mbps.
Is there any explanation of that or this is more likely to be Corvil monitoring device inaccuracy/mistake.
I have noticed as well that the traffic which seems to cause this spike is UDP video traffic.
Thanks in advance.
Anna
11-28-2012 04:54 AM
Hi Giuseppe,
What you say makes sense, however can you explain the discrepancy on the packets per second count? (144pps vs. 148pps)
Thanks,
Phil
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