Per Site QOS policy with Cisco IOS-XE

Wes Tribble westribble at gmail.com
Wed May 1 21:03:00 UTC 2013


I have a question for the QOS gurus out there.

                We are having some problems with packet loss for our
smaller MPLS locations.  This packet loss is due to the large speed
differential on our Hub site(150mb/s) in comparison the the branch office
locations(single T-1 to 4.5mb/s multilinks).  This packet loss only seems
to impact really bursty applications like our Web Proxy.  I have been
around and around with WindStream to give me some extra buffer or enable
random early detection on the smaller interfaces in my MPLS network.  So
far they are unwilling to do a custom policy and none of their standard
policies have enough buffer to handle the bursts.  They do FIFO tail drop
in every queue, so I can’t even choose a policy that has WRED implemented.



                I am looking for a way to solve the problem on my side.  I
can create a shaper for the proxy and match off an access-list to the
smaller sites, but I am either forced to do bandwidth reservations for each
site, or have multiple sites share the same shaper.  Here is an example of
what I was playing around with:



ip access-list extended ProxyT1Sites

 permit tcp any host 10.x.x.x 10.x.x.x 0.0.0.255

 permit tcp any host 10.x.x.x 10.x.x.x 0.0.0.255



class-map match-any ProxyShaperT1

match access-group name ProxyT1Sites



policy-map WindStream

class VOICE

  priority percent 25

  set dscp ef

class AF41

  bandwidth percent 40

  set dscp af41

  queue-limit 1024 packets

class ProxyShaperT1

  shape average 1536

  bandwidth percent 1

  set dscp af21

  queue-limit 1024 packets

class class-default

  fair-queue

  set dscp af21

  queue-limit 1024 packets





Another Idea I had was to create a bunch of shaper classes all feeding the
same child policy for priority queuing and bandwidth reservations based on
DSCP markings.  I’m just not exactly sure that this is allowed or
supported.  I also would run out of bandwidth allocation on the policy if I
use the true bandwidth number of 150mb/s. It is on a Gig port so I could
just take the bandwidth statement off of the interface to give myself
enough room for all of the shaper allocations.



Something like this(I am omitting the access-list that matches the branch
subnet and class map for brevity):



policy-map PerSiteShaper

class FtSmith

  shape average 1536

  bandwidth 1536
 service policy Scheduler
class Dallas

  shape average 4500

  bandwidth 4500
  service policy Scheduler
class NYC

  shape average 100000

  bandwidth 100000
  service policy Scheduler
class-default
  service-policy Scheduler

policy-map Scheduler
class VOICE

  priority percent 25

  set dscp ef

class AF41

  bandwidth percent 40

  set dscp af41

  queue-limit 1024 packets

class class-default

  fair-queue

  set dscp af21

  queue-limit 1024 packets






Just looking for some ideas that do not involve building tunnels to our
remote offices.  Thanks in advance,



*Wes Tribble*


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