Lately we have been getting bandwidth hogging when any user attempts to download updates / youtube / anything large files. The rest of the network is clogged. We have a fibre 20meg line in.

20meg Fibre -> SRX 220 -> Powerconnect 6248 -> Patch Panel -> Users.

We have COS setup on our SRX220 firewall to prioritise traffic to certain server IP addresses in and out to the cloud.

The switches are 2x powerconnect 6248 and are not stacked. They both have RSTP configured on them, and are pretty much default as the rest.

Server is 2012 R2 Essentials Running DNS / DHCP / AD.

I'm not sure on which layer to continue to address this problem. Should I be setting COS on the switches too? I would think the switches would be managing the traffic on their own be default..

I know this thing is really tricky to pinpoint, but are there any clues / logs to look at / potential settings that might be controlling this hogging that I can at least rule out?


  • Controlling incoming traffic is difficult. Your bandwidth has already been used by the time you see the traffic. QoS is most effective for intra-site or outbound traffic. You can attempt to control outbound TCP, but that is a pretty inexact way to try to control inbound TCP. If it is UDP, all you can really do is police it as it comes in.
    – Ron Maupin
    Commented Oct 12, 2016 at 4:14
  • (1) what does "The rest of the network is clogged" mean exactly? Do they get poor Internet performance or even poor LAN performance? (2) How are you prioritizing on the SRX exactly, where are you doing the marking and where are you applying QoS and what type? (3) If the problem is one user hogging the entire 2meg then would it be an option to configure traffic shaping on the inside interface (shaping the traffic from the Internet to the user)?
    – hertitu
    Commented Oct 12, 2016 at 10:51
  • (1) Network clogged I mean no one can access the internet - e.g. browsing to time.com sits there indefinitely until the download finishes / crawls in very slowly over minutes instead of seconds. - other LAN performance is perfectly fine however e.g. browsing file server. (2) COS has Scheduler maps defined for a group of cloud server IPs. (3) Yes shaping traffic on the inside would be a good solution, however I thought the switches would be "load balancing" all the requests and serving them equally?
    – leo_cape
    Commented Oct 12, 2016 at 22:26
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Commented Aug 15, 2017 at 4:21

1 Answer 1


QoS mechanisms only come into effect when there is congestion on the link. If you have a 20M circuit but connected to a 1G interface, your device will never recognize the congestion because the traffic never reaches 1G.

You need to implement inbound policing and outbound traffic shaping at your CIR (commited information rate) of your circuit, which would be 20M. Then your device will recognize that it is becoming congested at 20M and will start using the QoS mechanisms.

Ron is correct about inbound traffic from the internet being hard to control, but if you police the traffic, the packet loss will cause TCP protocol to back off and hopefully not overwhelm your circuit from one traffic flow.

  • Thanks John K - would they be on the switch side only or policing on the router?
    – leo_cape
    Commented Oct 27, 2016 at 8:09
  • You would want to police at the interface where your internet circuit connects. Policers are used for the inbound traffic coming from the circuit. You configure a bandwidth limit and traffic over that limit will be dropped.
    – John K.
    Commented Oct 27, 2016 at 13:45
  • Traffic shaping is used for outbound traffic and you set a limit similar to a policier, but in this case the router will buffer the traffic that violates the bandwidth limit instead of dropping it. So it attempts to save the packets and send them. I haven't set this up on an SRX before but I did a quick search and this might point you in the right direction: kb.juniper.net/InfoCenter/…
    – John K.
    Commented Oct 27, 2016 at 13:48
  • Another Juniper article juniper.net/documentation/en_US/junos12.3/topics/topic-map/…
    – John K.
    Commented Oct 27, 2016 at 13:49

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