Cisco QoS DSL – Simple QoS Policy on Cisco 877 Not Working

ciscodslqos

I'm trying to get a fairly simple QoS policy up and running on my DSL line using a Cisco 877. My aims are fairly simple – make sure that realtime and management stuff like RTP and SSH works regardless of congestion, then make sure that HTTP, FTP, SMTP etc. protocols get a good shout in times of congestion and throttle back things like bittorrent when things get busy.

I've tried applying the config below, but it seems to have no effect. If I pull down a couple of ubuntu torrents, and also download a large file via HTTP, the HTTP download slows to a crawl, whereas the torrents merilly carry on downloading at 300kbps+. The only effect it seems to have is upstream bittorrent slows to about 0.1kbps.

My understanding is that I need to have a policy applied outbound on my ATM subinterface, and inbound on the VLAN so the router knows how to deal with the different packets flowing in both ways. I tried adding a police only policy inbound on the ATM subinterface, but again, this seemed to make no difference. Bittorrent incoming traffic romps over everything.

Oddly, no matter how much I try and configure it, I can't get the Packet-Queueing policy to show up outbound on the ATM0.1 interface. The inbound one shows up fine.

Any ideas?

class-map match-any BESTEFFORT
 match protocol http
 match protocol secure-http
 match protocol icmp
 match protocol secure-imap
 match protocol smtp
 match protocol ipsec
 match protocol dns
class-map match-any REALTIME
 match protocol rtp
 match protocol rtcp
 match protocol sip
 match protocol ssh
class-map match-any SCAVENGER
 match protocol bittorrent
!
!
policy-map Packet-Queueing
 class REALTIME
    priority 400
 class BESTEFFORT
    bandwidth percent 50
     random-detect
 class SCAVENGER
    bandwidth percent 5
     random-detect
 class class-default
    fair-queue
     random-detect
!
policy-map Input-Police
 class SCAVENGER
   police rate 8000 bps
     conform-action transmit
     exceed-action drop
!
policy-map Packet-Tagging
 class REALTIME
  set precedence 5
 class BESTEFFORT
  set precedence 4
 class SCAVENGER
  set precedence 0
!
!
interface ATM0
 description ATM ADSL Interface
 no ip address
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 no atm ilmi-keepalive
 dsl operating-mode adsl2
 dsl enable-training-log
 !
!
interface ATM0.1 point-to-point
 pvc 0/38
  vbr-rt 886 886
  encapsulation aal5mux ppp dialer
  dialer pool-member 1
  service-policy in Input-Police
 !
interface Vlan1
 description internal private VLAN
 ip address 192.168.0.1 255.255.255.0
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 ip flow ingress
 ip nat inside
 ip virtual-reassembly
 ip route-cache same-interface
 ip tcp adjust-mss 1452

 service-policy input Packet-Tagging
 hold-queue 100 out
!

Best Answer

The fundamental problem you have is that QoS in the inbound direction (in to your router) to control traffic headed in your direction is relatively useless.

The congestion is occurring at the egress of the ISP device to which your Router attaches. That ISP interface has no relevant QoS applied - it is most certainly a FIFO queue. Thus if the bittorrent end points are sending you data faster than your HTTP end point, bittorrent wins in a classic FIFO queue and your HTTP download is starved.

This is a very common problem in almost every home networking setup. Bittorrent can easily starve not only SSH or RTP traffic, but VoIP traffic as well.

Use your Bittorrent software's built in rate limiting to cap up and down speeds at a rate lower than what is available.

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