max-reserved-bandwidth

Answered Question
Apr 1st, 2008
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Available Bandwidth shown under the sh interface output is 384K(75% of the total bandwidth, 512 K).


Will making the Available bandwidth 512 K by using max-reserved-bandwidth affect traffic like routing updates if we are not configuring any Qos on the router?


The aim is just to get an output of "Available bandwidth 512 kilobits/sec" under show interface output.



sh int se 0/0/0

Serial0/0/0 is up, line protocol is up

Hardware is GT96K Serial

Description: Connected to

Internet address is

MTU 1500 bytes, BW 512 Kbit, DLY 20000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation HDLC, loopback not set

Keepalive set (10 sec)

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters 1d18h

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/3/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

Available Bandwidth 384 kilobits/sec


Correct Answer by Joseph W. Doherty about 8 years 12 months ago

"The aim is just to get an output of "Available bandwidth 512 kilobits/sec" under show interface output."


If your aim is only cosmetic, I would recommend you don't change the maximum reserved. Actual usuable bandwidth isn't lost to other classes, and even if you don't cause any issues with your current CBWFQ policies today, you could set yourself up for issues in the future.

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Goutam Sanyal Tue, 04/01/2008 - 00:19
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Aneesh


Router(config-if)#bandwidth ? (put the 512)

<1-10000000> Bandwidth in kilobits

inherit Specify that bandwidth is inherited

receive Specify receive-side bandwidth

Router(config-if)# max-reserved-bandwidth 100


Hope it will work.


Thanks Goutam


royalblues Tue, 04/01/2008 - 00:54
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It should not..


The reason you are seeing the available bandwidth as 75% of the actual bandwidth is due to WFQ.

The routing updates would be generally tagged with IP precedence 6 and 7

WFQ is IP Precedence-aware, that is, it is able to detect higher priority packets marked with precedence by the IP Forwarder and can schedule them faster, providing superior response time for this traffic


HTH

Narayan

Goutam Sanyal Tue, 04/01/2008 - 01:03
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Narayan, Its default with Cisco Serial Interface. If my network run with any routing protocol, then for the same I will get 25% less BW then my present? Goutam

aneesh.ts Tue, 04/01/2008 - 01:13
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Hi narayan,


What you told really make sense. If bandwidth allocation using QoS is not done the traffic should go as decided by WFQ even if max-reserved-bandwidth 100 is configured.


But if bandwidth allocation is done using Qos i think we should create a seperate class for (class 6 & 7) network control traffic if we are trying to allocate the whole 100% of bandwidth.

royalblues Tue, 04/01/2008 - 05:19
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Yes it is always desirable to have a seperate class defined for routing protocols (using DSCP CS6, CS7) and allocate some amount of bandwidth


Narayan

Correct Answer
Joseph W. Doherty Tue, 04/01/2008 - 06:33
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"The aim is just to get an output of "Available bandwidth 512 kilobits/sec" under show interface output."


If your aim is only cosmetic, I would recommend you don't change the maximum reserved. Actual usuable bandwidth isn't lost to other classes, and even if you don't cause any issues with your current CBWFQ policies today, you could set yourself up for issues in the future.

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