QoS Frame relay fragmentation with the CBWFQ

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Feb 3rd, 2010
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Dear All,

I configured QoS for remote branches the bandwidth link is 256 so i need to configure frame relay fragmentation but when i configure it under the sub interface the router hang and to solve the problem i should delete the fragmentation to access the router from the same session and CPU was raising to 50%. my question is have i configure the fragmentation at the both sides on one only?


Mohamed Taher

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Mohamed Sobair Wed, 02/03/2010 - 06:51
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If you have sensitive application such as VOIP, then I recommend to have FRF on both sides implemented , this should have affect on the serialization delay.

Frame-relay fragmentation decreases the delay over the WAN link, however , you shouldnt notice hanging other than higher delay on the opposite direction of the WAN.



mohamed.taher Wed, 02/03/2010 - 07:02
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Hi Mohamed

     the other side link speed is 2 M so i think i dont need fragmentation. but my main issue is the router hanging i notice also than the number of frame with unexpected b bit is very high do you have what this is meaning?


Mohamed Taher

Mohamed Sobair Thu, 02/04/2010 - 00:42
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Hi Mohamed,

Thats a bad sign.

If the B bit is increasing , then it means the Number of fragments received by this DLCI that have an unexpected B bit set. When this occurs, all fragments being reassembled are dropped and a new frame is begun with this fragment

So the fragmented packets are dropped and it could be causing high delay and application interrupt.

Please post your current FRF config



mohamed.taher Sun, 02/07/2010 - 00:27
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Hi Mohamed,

Here is the configuration below:

class-map match-all mail
match access-group name mail
class-map match-all update
match access-group name updates
class-map match-all SAP
match access-group name SAP
class-map match-all voice
match access-group name voice
policy-map QOS
class voice
  priority percent 30
class update
  bandwidth percent 10
class SAP
  bandwidth percent 40
class mail
  bandwidth percent 15

interface Serial0/0/0
bandwidth 256
no ip address
encapsulation frame-relay IETF
no fair-queue
frame-relay traffic-shaping
frame-relay lmi-type ansi
max-reserved-bandwidth 95
interface Serial0/0/0.1 point-to-point
ip address
frame-relay class QOS
frame-relay interface-dlci 16

ip access-list extended SAP
permit ip any host
permit ip any host
permit ip any host
permit ip any host
permit ip any host
permit ip any host
ip access-list extended mail
permit ip any host
ip access-list extended updates
permit ip any host
permit ip any host
permit ip any host
permit ip any host
ip access-list extended voice
permit udp any any range 16384 32767
permit tcp any eq 1720 any
permit tcp any any eq 1720
permit tcp any eq 1970 any
permit tcp any any eq 1970
permit udp any any eq 4569
permit udp any any eq 5036
permit udp any any eq 5060
map-class frame-relay QOS
frame-relay fragment 320
frame-relay traffic-rate 256000 256000
service-policy output QOS


Mohamed Taher


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