04-15-2009 05:45 AM - edited 03-04-2019 04:22 AM
I have the below policy attached to s0/0/0 - (service-policy output ETMS) Is the 256 being set aside until use?
policy-map ETMS
class SILVER
set ip dscp af31
bandwidth 256
04-15-2009 05:49 AM
256kbps is guarantee bandwidth for class SILVER while the interface is under congestion.
Under normal load, class SILVER can potentially use more than 256kbps of bandwidth.
__
Edison.
04-15-2009 08:47 AM
"Is the 256 being set aside until use?"
No. (It's a guarantee that the SILVER class of traffic should be able to obtain at least that much bandwidth. [As Edison also notes.] Class bandwidth not used, is available to other traffic classes.)
04-15-2009 09:32 AM
One more question. The "available bandwidth" string under show int s0/0/0.
Is that the bandwidth currently available?
Hardware is GT96K with integrated T1 CSU/DSU
MTU 1500 bytes, BW 384 Kbit, DLY 20000 usec,
reliability 255/255, txload 13/255, rxload 248/255
Encapsulation FRAME-RELAY IETF, loopback not set
Keepalive set (10 sec)
LMI enq sent 4585, LMI stat recvd 4585, LMI upd recvd 0, DTE LMI up
LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0
LMI DLCI 1023 LMI type is CISCO frame relay DTE
FR SVC disabled, LAPF state down
Broadcast queue 0/64, broadcasts sent/dropped 764/0, interface broadcasts 0
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters 12:44:07
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: Class-based queueing
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/46/128 (active/max active/max total)
Reserved Conversations 2/2 (allocated/max allocated)
****Available Bandwidth 24 kilobits/sec****
5 minute input rate 374000 bits/sec, 43 packets/sec
5 minute output rate 21000 bits/sec, 29 packets/sec
2052446 packets input, 2008412730 bytes, 0 no buffer
04-15-2009 09:36 AM
That value reflects the bandwidth available for reservation. It does not reflect the available bandwidth for flows traversing this interface.
___
Edison.
04-15-2009 09:42 AM
and when you say "reservation" you mean the policy?
04-15-2009 09:42 AM
Eric,
Avaliable bandwidth means as the name implies. You are allowed to use 75% of bandwidth by default. 25% is allocated for class-default. Let's say.
- Link bandwidth = 1024 kbps
- You are allowed to use 768 kbps. 75% of 1024
- You have assigned 256 kpbs for SILVER class
As a result. Available bandwidth is 768 - 256 = 512
Am I clear?
HTH,
Toshi
04-15-2009 09:49 AM
Thanks guys, I got it!!
04-15-2009 10:58 AM
To clarify what Toshi is saying, it's not really "allowed to use" but more so "allowed to define" with bandwidth statements. Actual traffic bandwidth utilization, for non-LLQ classes, isn't normally limited by the bandwidth statement.
On many router platforms, by default, you can not define bandwidth statements that sum more than 75%. (NB: default can be overridden, and limitations differ on diffent platforms and/or very recent IOSs which support HQF.)
04-15-2009 11:00 AM
Joseph,
Thanks for fixing my words. That's right.
Like you mentioned, Available bandwidth is the rest of bandwidth we can define. All depend on the bandwidth command you configured within the interface level.
5P! for you
Toshi
04-15-2009 11:04 AM
Toshi:
Nice post, buddy.
Queick question regarding the default.
Can you elaborate a bit more on that default of 25%. Where is that standard written so I could read up on it?
Thanks
Victor
rated your post, too
04-15-2009 11:13 AM
"You can configure class policies for as many classes as are defined on the router, up to the maximum of 64. However, the total amount of bandwidth allocated for all classes included in a policy map must not exceed 75 percent of the available bandwidth on the interface. The other 25 percent is used for control and routing traffic. (To override the 75 percent limitation, use the max-reserved bandwidth command.) If not all of the bandwidth is allocated, the remaining bandwidth is proportionally allocated among the classes, based on their configured bandwidth. "
From http://www.cisco.com/en/US/docs/ios/12_0t/12_0t5/feature/guide/cbwfq.html#wp25081
04-15-2009 11:16 AM
Victor,
The 25 % of the bandwidth is reserved for the important/critical traffic like L2 keepalives and other system critical frames/packets/routing traffics
Usage Guidelines
The sum of all bandwidth allocation on an interface should not exceed 75 percent of the available bandwidth on an interface. The remaining 25 percent of bandwidth is used for overhead, including Layer 2 overhead, control traffic, and best-effort traffic.
If you need to allocate more than 75 percent for RSVP, CBWFQ, LLQ, IP RTP Priority, Frame Relay IP RTP Priority, and Frame Relay PIPQ, you can use the max-reserved-bandwidth command. The percent argument specifies the maximum percentage of the total interface bandwidth that can be used.
Please check out this link.
http://www.cisco.com/en/US/docs/ios/12_3t/qos/command/reference/qos_m1gt.html#wp1113113
You can use a "max-reserved-bandwidth" command to override the default.
5P! for you Victor
Toshi
04-15-2009 03:07 PM
Toshi, you kill me...lol
YOU are the one who deserves the 5P for this one, my friend - and I gave it to you.
Thanks
V
08-30-2009 04:45 AM
Toshi,
I am interested with the remaining 25% as well. Its said that the remaining 25% is for control traffic also. My questions are:
1. By default, if we do not specify a particular class for control traffic, then it will be included in this 25% class-default right?
2. Regarding my first question, does this guarantee that the control traffic will be able to pass through a link when congestion occur? coz in my opinion, if we do it like this (doesn't specify a particular class for control), there's a possibility that the control traffic gets dropped or doesnt get through when the link is congested. Am I right?
3. On the other hand, if I specify a particular class for control traffic, so its okay then if i override the default bandwidth to be used to 100% by using the command "max-reserved-bandwidth 100", right?
Regards,
Even
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