Re: Understanding QoS

Keep in mind with QoS, if your access-rate and CIR are different (ie a
10Mbps circuit delivered of a GigE port), you need to set up QoS to operate
in the context of 10Mbps (aka shaper). A simple bandwidth command on the
interface doesn't do anything. The router cheerfully allows itself to
exceed the "bandwidth xx" amount, up to the access rate of the interface.

And it's worth considering shaping to 95% of CIR rather than 100%, to take
into account the shaper burst and any overhead (GRE, etc.,) that some
platforms don't take into account when calculating the egress rate. For
example, Juniper routers don't account for GRE overhead added when
calculating how much bandwidth is passing through an interface. So, taking
that into account and the burst allowed by the shaper, you may be sending
more than your provider allows, resulting in premature drops.

Also, always remember that with very few exceptions, QoS works only for
outbound traffic. Just because you've enabled QoS on a router doesn't mean
the router on the other side has enabled QoS coming towards you. And since
most sites download more data than they upload, it's very often the router
on the other side where the congestion is occurring.

Regarding your question about the 75% - I think you're referring to the
default limitation for allocating BW from a policy-map. Unless you use
max-reserved-bandwidth command, you can only allocate 75% of the
access-rate of the interface. That doesn't mean though the bandwidth can't
be used. It just means that by default you can't allocate more than that.

On Thu, Jun 27, 2013 at 6:13 PM, marc edwards <renorider_at_gmail.com> wrote:

> How can I verify it there is indeed a congestion
> happened?
>
> DC1-3FL-RTR001#sh policy-map int g0/2 GigabitEthernet0/2
> Class-map: class-default (match-any)
> drop rate 0000 bps
>
> This would be the first queue to start dropping packets during congestion
> event.
>
> Marc Edwards
> CCIE #38259
>
>
> On Thu, Jun 27, 2013 at 4:47 PM, Cisco Fanatic <ebay_products_at_hotmail.com
> >wrote:
>
> > Studying QoS and playing
> > with it ... quick dummy questions ..
> >
> >
> >
> > Ok, I have
> > this policy
> >
> >
> >
> > !
> >
> > policy-map
> > QoS_Output_Policy
> >
> > class VoIP
> >
> > priority
> > percent
> > 35
> >
> > set ip dscp ef
> >
> > class Video
> >
> > priority percent
> > 25
> >
> > set ip
> > dscp af41
> >
> > class SIP
> >
> > bandwidth
> > remaining percent 25
> >
> > set ip dscp af31
> > class Data
> >
> > bandwidth
> > remaining percent 15
> >
> > set ip dscp af21
> >
> > class
> > class-default
> >
> > fair-queue
> >
> > set dscp default
> >
> > !
> >
> > !
> >
> > interface
> > GigabitEthernet0/2
> >
> > duplex full
> >
> > speed 100
> >
> > service-policy
> > output
> > QoS_Output_Policy
> >
> > !
> >
> >
> >
> > * Is by default 75%
> > (75MB) of 1 GB bandwidth is
> > available for use?
> >
> > * I can't apply
> > "max-reserved-bandwidth" to a gig
> > interface. How can I use the total
> > 1GB bandwidth?
> >
> > * "priority percent
> > 35"
> > means LLQ and VoIP class gets 26MB (75MB * 35%)?
> >
> > * "bandwidth
> > remaining
> > percent 25" SIP traffic gets 12MB (75MB - 26MB = 46MB * 25% =
> > 12MB)?
> >
> > * How
> > can I verify it
> > there is indeed a congestion happened?
> >
> >
> >
> > DC1-3FL-RTR001#sh
> > policy-map int g0/2
> >
> > GigabitEthernet0/2
> >
> >
> >
> > Service-policy
> > output:
> > QoS_Output_Policy
> >
> >
> >
> > queue stats
> > for all priority classes:
> > Queueing
> >
> >
> > queue limit 64 packets
> >
> >
> > (queue depth/total
> > drops/no-buffer drops) 0/0/0
> >
> >
> > (pkts output/bytes output)
> > 60579572/8599620493
> >
> >
> >
> > Class-map:
> > VoIP (match-any)
> >
> >
> > 58813111
> > packets, 8056468225 bytes
> >
> > 5
> > minute offered rate 0000 bps, drop rate
> > 0000 bps
> >
> >
> > Match: ip dscp ef (46)
> >
> >
> > 1167959 packets, 86399962
> > bytes
> >
> >
> > 5 minute rate 0 bps
> >
> >
> > Match: protocol rtp audio
> > 57632956 packets, 7968100335 bytes
> >
> >
> > 5 minute rate 0 bps
> >
> >
> > Match:
> > protocol rtcp
> >
> >
> > 12196 packets, 1967928 bytes
> >
> >
> > 5 minute rate 0
> > bps
> >
> >
> > Priority: 35% (35000 kbps), burst bytes 875000, b/w exceed drops: 0
> > QoS
> > Set
> >
> >
> > dscp ef
> >
> >
> > Packets marked 58813111
> >
> >
> >
> > Class-map:
> > Video (match-any)
> >
> >
> > 1766463 packets, 543152268 bytes
> >
> > 5
> > minute
> > offered rate 0000 bps, drop rate 0000 bps
> >
> >
> > Match: ip dscp af41 (34)
> > 1653227 packets, 526896986 bytes
> >
> >
> > 5 minute rate 0 bps
> >
> >
> > Match:
> > protocol rtp video
> >
> >
> > 0 packets, 0 bytes
> >
> >
> > 5 minute rate 0 bps
> > Match: protocol video-over-http
> >
> >
> > 0 packets, 0 bytes
> >
> >
> > 5 minute
> > rate 0 bps
> >
> >
> > Match: access-group name video
> >
> >
> > 113236 packets,
> > 16255282 bytes
> >
> >
> > 5 minute rate 0 bps
> >
> >
> > Priority: 25% (25000 kbps),
> > burst bytes 625000, b/w exceed drops: 0
> >
> >
> >
> > QoS
> > Set
> >
> >
> > dscp af41
> > Packets marked 1766463
> >
> >
> >
> > Class-map:
> > SIP (match-any)
> >
> >
> > 1125626
> > packets, 314867881 bytes
> >
> > 5
> > minute offered rate 6000 bps, drop rate 0000
> > bps
> >
> >
> > Match: ip dscp af31 (26)
> >
> >
> > 572572 packets, 98559349 bytes
> > 5 minute rate 3000 bps
> >
> >
> > Match: protocol sip
> >
> >
> > 553043 packets,
> > 216307750 bytes
> >
> >
> > 5 minute rate 3000 bps
> >
> >
> > Match: ip dscp cs3 (24)
> > af31 (26)
> >
> >
> > 11 packets, 782 bytes
> >
> >
> > 5 minute rate 0 bps
> > Queueing
> >
> >
> > queue limit 64 packets
> >
> >
> > (queue depth/total
> > drops/no-buffer drops) 0/0/0
> >
> >
> > (pkts output/bytes output)
> > 1125626/314867881
> >
> >
> > bandwidth remaining 25%
> >
> > QoS
> > Set
> >
> >
> > dscp
> > af31
> >
> >
> > Packets marked 1125626
> >
> >
> >
> > Class-map:
> > Data (match-any)
> > 0
> > packets, 0 bytes
> >
> > 5
> > minute offered rate 0000 bps, drop rate 0000 bps
> > Match: ip dscp af21 (18)
> >
> >
> > 0 packets, 0 bytes
> >
> >
> > 5 minute rate 0
> > bps
> >
> >
> > Queueing
> >
> >
> > queue limit 64 packets
> >
> >
> > (queue depth/total
> > drops/no-buffer drops) 0/0/0
> >
> >
> > (pkts output/bytes output) 0/0
> > bandwidth remaining 15%
> >
> > QoS
> > Set
> >
> >
> > dscp af21
> >
> >
> > Packets
> > marked 0
> >
> >
> >
> > Class-map:
> > class-default (match-any)
> >
> >
> > 791611850
> > packets, 912546925544 bytes
> >
> > 5
> > minute offered rate 16514000 bps, drop
> > rate 0000 bps
> >
> >
> > Match: any
> >
> >
> > Queueing
> >
> >
> > queue limit 64 packets
> > (queue depth/total drops/no-buffer drops/flowdrops) 0/5/0/5
> >
> >
> > (pkts
> > output/bytes output) 791611623/912502991512
> >
> >
> > Fair-queue: per-flow queue
> > limit 16 packets
> >
> > QoS
> > Set
> >
> >
> > dscp default
> >
> >
> > Packets
> > marked 791481954
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Thu Jun 27 2013 - 19:49:51 ART