I can see you have a load-interval of 30 sec on the interface. That's good.
So do a ping that would last for a few minutes, then open another telnet session (while that ping is still running) and check things out with sh policy-ma int. Then we can have more reliable stats . On 25 February 2012 00:35, George Leslie <[email protected]>wrote: > > Hi Kim,Right, I've gotcha. you have CIR set to 20000, and Bc to 500. That > gives at Tc of 25 ms ( 500 bits / 20000 bps). However, the size of your > token bucket is 500/8 = 62.5 bytes, and excess burst the same. So, when a > 100 byte ping arrives, it is > Bc so has exceeded the CIR for that > timeslot. So shaping is active. It needs to wait for the second Tc for a > Be to accumulate before it can be sent. Also, and something I don't know > (it would need a sniffer)... I see your round trip time is 12ms. If IOS > release the next ping as soon as it gets the previous reply back, it could > be releasing pings at t = 0ms, t = 12ms and t = 24 ms. That could be 300 > bytes of payload, trying to use 62.5 bytes of Bc. Shaping would definitely > be active!! I see you configured just the average shaping rate with no > explicit Bc or Be. IOS has picked default of 25ms. If you read Odom, it > states that if shaping rate is < 320kbps, then it should default to 8000 > bits of Bc and Be. Clearly this di > d not happen here. I did notice that you have no bandwidth command on the > serial. Interesting to see the change in Bc and Be if you put "bandwidth > 128" on the interface, so see if IOS is picking up the rate, not from the > shape command but from the interface bandwidth command??? Or you try an > explicit set of Bc to 8000 bits to see the difference... George. > Subject: Re: [OSL | CCIE_RS] Shaping and shaping queues - OT > From: [email protected] > Date: Fri, 24 Feb 2012 23:40:03 +0100 > CC: [email protected] > To: [email protected] > > > > Hi George, > I actually do have the book, and have read it more than once concerning > this issue. > In the book, it is clearly stated that when shaping is not active (i.e.. > you are able to use tokens from your token-bucket to send the packet), your > packet bypasses the entire shaping queues and next step is into software > queues (only if the hardware queue is full). This is clearly illustrated on > page 377. > Interface congestion is a another discussion completely, because thats > where your software queues comes into place as well as the scheduling > mechanism for emptying these. > So lets say that my 3 packets arrive at the same time. They are conforming > to my shaping policy, so theres no need to put these into shaping queues > and invoke that scheduler. Instead, if the hardware queue is full (3-4 > packets) the packets would go into the software queues. > The two are completely separate queues. > My issue with the thing is basically that even if you don't shape > anything, Ie. send a packet every 3-4 seconds, it still gets incremented in > the output of "show policy-map int" statistics. This is counter-intuitive > to me. > Hope that clarifies it. > Thanks, > > On Feb 24, 2012, at 11:18 PM, George Leslie wrote:Hi Kim, > If you have read the Wendell Odom guide about QoS, then the answer is in > there. > > The issue comes with what "congestion" means in terms of QoS. > > A lot of people believe, as you state below, that: > > congestion means offered rate > shaped rate. > > While this is certainly true, there is another caveat with this. > > Actually, shaping comes active when there is no room left in the tx-ring > (aka hadware queue) of the interface. The imposition of certain queueing > techniques makes IOS decrease the number of packets that can be held in the > hardware queue to a very low value, something like 2-3 packets (I forget > the exact number but it is shown in the Odom guide). > > So, shaping becomes active when a packet arrives when there is no room > left in the very small interface hardware queue. At this point, it is held > in the shaping queues and shaping stays active until the queues empty. > > So, all that needed to happen in your case was 3 packets to arrive at the > interface at the same time, and BAM...shaping is active. After that, > subsequent packets that arrive are subject to shaping, and held in the > shaping queues. While in the shaping queues, the scheduler picks packets > for release based on the child policy: > > so child policy will determine the next packet to get sent, but parent > policy selects the shaping rate and when it is released. As the shaping > rate is almost certainly less than line speed of the outbound interface, > this helps ensure that shaping is active most of the time. > > This is what you want!!! If you shape traffic at all, it is to get round > another issue e.g. central site blocking, speed mismatch between hub and > spoke sites, CIR purchased from WAN provider, that sort of thing. You want > shaping to be active, so YOU, via the child policy, can determine the > packets that get released, their order (i.e priority vs. bandwidth > allocation etc). > > As my old physics teacher used to say, perform a little thought experiment > here. > > Let's say that the same rule applies, that shaping only becomes active > when the hardware queue is full (this makes sense, as if the hardware is > NOT full, why bother to put a packet through shaping queues when it will > get straight through them into the hardware queue anyway). Imagine that > the hardware queue could contain 1,000,000,000,000 packets. This would > mean that shaping would NEVER become active, the whole queue becomes a FIFO > queue, and you have no control over the order of packet release. > > By setting the size of the hardware queue artificially low, it makes > shaping become active much earlier, which gives you the control. > > HTH, at least this is my understanding. > > George > > > > > Date: Fri, 24 Feb 2012 14:00:46 +0100 > > From: [email protected] > > To: [email protected]; [email protected] > > Subject: [OSL | CCIE_RS] Shaping and shaping queues - OT > > > > Hi All, > > > > When using shaping and shaping queues, i ran into a behavior i didnt > expect. > > > > According to QoS exam guide, packets should only enter shaping queues > > when shaping is active. If shaping is not active (packets are > > conforming) it should bypass the shaping queues and go directly to > > software queues and then TX-ring. > > > > For example, defining our PARENT policy: > > > > policy-map OVERALL > > class class-default > > shape average 20000 > > service-policy SUB-POL > > > > And our "CHILD" policy: > > > > policy-map SUB-POL > > class ICMP > > priority 10 > > class SSH > > bandwidth 8 > > class TELNET > > > > And applying the OVERALL policy outbound on an interface: > > > > R2(config-if)#do sh run int s0/1/0 > > Building configuration... > > > > Current configuration : 132 bytes > > ! > > interface Serial0/1/0 > > ip address 192.168.25.2 255.255.255.0 > > load-interval 30 > > no keepalive > > clock rate 128000 > > service-policy output OVERALL > > end > > > > I would expect my packets NOT to hit any shaping queues unless they > > exceed 20kbit > > > > Doing a ping reveals a different behavior: > > R2#ping 192.168.25.5 rep 50 > > > > Type escape sequence to abort. > > Sending 50, 100-byte ICMP Echos to 192.168.25.5, timeout is 2 seconds: > > !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.!!!!!!!!! > > Success rate is 98 percent (49/50), round-trip min/avg/max = 12/14/16 ms > > R2#sh policy-map int > > Serial0/1/0 > > > > Service-policy output: OVERALL > > > > Class-map: class-default (match-any) > > 51 packets, 5324 bytes > > 30 second offered rate 3000 bps, drop rate 2000 bps > > Match: any > > Queueing > > queue limit 64 packets > > (queue depth/total drops/no-buffer drops) 0/1/0 > > (pkts output/bytes output) 50/5420 > > shape (average) cir 20000, bc 500, be 500 > > target shape rate 20000 > > > > Service-policy : SUB-POL > > > > queue stats for all priority classes: > > Queueing > > queue limit 64 packets > > (queue depth/total drops/no-buffer drops) 0/1/0 > > (pkts output/bytes output) 49/5096 > > > > Class-map: ICMP (match-all) > > 50 packets, 5000 bytes > > 30 second offered rate 2000 bps, drop rate 2000 bps > > Match: protocol icmp > > Priority: 10 kbps, burst bytes 1500, b/w exceed drops: 1 > > > > > > Class-map: SSH (match-all) > > 0 packets, 0 bytes > > 30 second offered rate 0 bps, drop rate 0 bps > > Match: protocol ssh > > Queueing > > queue limit 64 packets > > (queue depth/total drops/no-buffer drops) 0/0/0 > > (pkts output/bytes output) 0/0 > > bandwidth 8 kbps > > > > Class-map: TELNET (match-all) > > 0 packets, 0 bytes > > 30 second offered rate 0 bps > > Match: protocol telnet > > > > Class-map: class-default (match-any) > > 1 packets, 324 bytes > > 30 second offered rate 0 bps, drop rate 0 bps > > Match: any > > > > queue limit 64 packets > > (queue depth/total drops/no-buffer drops) 0/0/0 > > (pkts output/bytes output) 1/324 > > > > > > As can be seen, all packets seems to traverse the Shaping queue ICMP, > > even though most of the packets (all near one according to this) > > should not be shaped. > > > > Anyone know if this is an implementation thing in IOS, that the > > counters will still be updated even though they in reality bypass the > > queues or if something else is going on here? > > > > Just curious. > > > > Sincerely, > > Kim Pedersen > > > > -- > > // Freedom Matters > > // CCIE #29189 > > // www.packet-forwarding.net > > _______________________________________________ > > For more information regarding industry leading CCIE Lab training, > please visit www.ipexpert.com > > > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > > > > http://onlinestudylist.com/mailman/listinfo/ccie_rs > > > > // Freedom MattersCCIE #29189http://www.packet-forwarding.net > > > > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > > http://onlinestudylist.com/mailman/listinfo/ccie_rs > -- -- Olugbenga Oyebande MD, DAIT 234-803-302-5287 http://www.dait-ng.com Cisco Networks, Network Security & Quality of Service DAIT Linux Enterprise Network Servers, Web Portal Projects Broadband Internet Deployment & ISP Consultancy _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
