03-17-2008 09:28 PM - edited 03-03-2019 09:10 PM
Dear all,
I have some question about QoS setting and bandwidth allocation.
Case 1:
Can i set overall QoS percentage exceed 100% like as below?
If can, how can it allocate the BW?
If the percentage set cannot exceed 100%, then what is the difference/purpose to set "priority" and "bandwidth", since they all use to reserve BW?
policy-map policy1
class voice1
priority percentage 40
class voice2
priority percentage 40
class data
bandwidth percentage 30
Case 2:
In case that the BW allocation is not 100%, how will the traffic drop if BW congest or non-congest?
policy-map policy1
class voice1
priority percentage 40
class data
bandwidth percentage 30
Thanks all,
Eric HUI
03-17-2008 10:39 PM
hi Eric,
The link connected through routers
has some IGP (ospf )traffic apart from data
traffic.so if you reserve the 100 % of total
bandwidth of the link, the ospf traffic will
not get priority so probelm may in convergence.
ospf changes,routing table will not be proper
so CISCO suggests to reserve only 75% of total traffic.
in the second case,with WRED enabled it tries to drops packets with low priority value
hope my post clarifies
rgds
shiva
03-18-2008 07:55 AM
Hi,
For case 1, is the configuration workable if the sum of percentage bandwidth has exceeded 100%? Also, how will the bandwidth be allocated?
For case 2,
If low priority value will be drop firstly, how is the packet identified as low priority?
Thanks,
Eric
03-18-2008 11:58 AM
I recall most routers won't accept CBWFQ of more than 100%, but can't recall whether that's while defining the policy map or when policy map is applied to interface.
There's a major difference between "priority" % and bandwidth %. The former sets a cap that the class can not exceed. The latter sets a minimum, but more may be used if available. The latter also sets ratios between different classes when they both want more bandwidth and it's available.
e.g.
class llq
priority % 10
class a
bandwidth % 10
class b
bandwidth % 20
class c
bandwidth % 30
If there's only traffic in classes a and c, and they both want all, they'll get 25% and 75%.
With regard to congestion drops, again "priority" will drop whenever its allocation is exceeded. The other classes, usually have a FIFO queue, which drops with queue packet overflow.
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